Aphasia is an acquired disorder of language due to brain damage. It may occur secondary to brain injury or degeneration and involves the left cerebral hemisphere to a greater extent than the right.
Aphasia develops abruptly in patients with a stroke or head injury. Patients with neurodegenerative diseases or mass lesions may develop aphasia insidiously.
People with aphasia may exhibit the following symptoms:
Patients may also experience problems with spoken and written language. Typically, reading and writing are more impaired than talking or understanding.
See Clinical Presentation for more detail.
Careful assessment of language function with an evaluation of neighborhood signs is important in the diagnosis of the localization and cause of aphasia. These signs include:
Bedside examination
Components of bedside language examination include assessments of spontaneous speech, naming, repetition, comprehension, reading, and writing. Although bedside examination can usually reveal the type of aphasia, formal cognitive testing by a neuropsychologist or speech/language therapist may be important to determine fine levels of dysfunction, to plan therapy, and to assess the patient's potential for recovery.
Imaging tests
Because aphasia is most often caused by stroke, neuroimaging is required to localize and diagnose the cause of aphasia. CT scanning and MRI are the mainstays of neuroimaging.
See Workup for more detail.
The treatment of a patient with aphasia depends on the cause of the aphasia syndrome. Acute stroke treatment for the aphasic patient, such as intravenous tPA, intra-arterial interventional treatments, carotid endarterectomy and stenting, or even blood pressure manipulation may help to alleviate the deficit. Surgery for a subdural hematoma or brain tumor may be beneficial. In infections such as herpes simplex encephalitis, antiviral therapy may help the patient recover.
If brain damage is mild, a person may recover language skills without treatment. However, most people undergo speech and language therapy to rehabilitate their language skills and supplement their communication experiences. Speech and language therapy is the mainstay of care for patients with aphasia.
See Treatment and Medication for more detail.
Aphasia is an acquired disorder of language due to brain damage. Aphasia does not include (1) developmental disorders of language, often called dysphasia in the United States; (2) purely motor speech disorders, limited to articulation of speech via the oral-motor apparatus, referred to as stuttering, dysarthria, and apraxia of speech; or (3) disorders of language that are secondary to primary thought disorders, such as schizophrenia.
Encompassed under the term aphasia are selective, acquired disorders of reading (alexia) or writing (agraphia). Closely related to aphasia are the family of disorders called apraxias (disorders of learned or skilled movements), agnosias (disorders of recognition), acalculias (disorders of calculation ability), and more global neurobehavioral deficits such as dementia and delirium. Such related syndromes may coexist with aphasia or exist independently.
Aphasia may occur secondary to brain injury or degeneration and involves the left cerebral hemisphere to a greater extent than the right. Language function lateralizes to the left hemisphere in 96–99% of right-handed people and in a majority of left-handed people. Of the remaining left-handed people, about one half have mixed hemisphere language dominance, and about one half have right hemisphere dominance. Left-handed individuals may develop aphasia after a lesion of either hemisphere, but the syndromes from left hemisphere injury may be milder or more selective than those seen in right-handed people, and they may recover better.
Most aphasias and related disorders are due to stroke, head injury, cerebral tumors, or degenerative diseases. The neuroanatomic substrate of language comprehension and production is complex, including auditory input and language decoding in the superior temporal lobe, analysis in the parietal lobe, and expression in the frontal lobe, descending via the corticobulbar tracts to the internal capsule and brainstem, with modulatory effects of the basal ganglia and the cerebellum.
Aphasia syndromes have been described based on patterns of abnormal language expression, repetition, and comprehension. These classical syndromes have been roughly correlated with specific left hemisphere locations, though clear overlaps and individual differences make the aphasia syndromes limited in specificity. Patients may lose the ability to produce speech, to comprehend speech, to repeat, and to hear and read words in many nuanced ways. Classical aphasia syndromes (see Aphasia syndromes in History) include global, Broca, Wernicke, and conduction aphasia, as well as transcortical motor, transcortical sensory, and transcortical mixed aphasia. Pure alexia and optic aphasia are often discussed with the classical aphasias.
Language function can be parsed in several important ways other than assignment to the classical aphasia syndromes. A variety of types of evidence have noted that certain specific language functions (such as naming pictures) activate widespread neural networks involving many parts of both hemispheres of the brain. Producing, receiving, and interpreting speech requires specific and distinct cognitive processes such as phonologic decoding and encoding, orthographic decoding and encoding (for reading), lexical access, lexical-semantic representations of words, and semantic interpretation of language. Differentiation of these processes involves testing patients with different aphasia types and attempting to find double dissociations among groups of patients to determine the neurologic basis of specific cognitive processes.
The lesion method, the principal source of information about aphasia from autopsy studies in the 19th and early to mid-20th centuries, and from brain imaging modalities since the 1970s, remains a useful source of information. However, it has been abetted by cortical stimulation studies, mainly in patients with epilepsy, and functional neuroimaging, such as fMRI and PET scanning often carried out during language testing in healthy individuals, to determine the language function of specific areas of the brain.
Data on incidence of aphasia in the United States are limited. Aphasia occurs in a variety of cerebrovascular, traumatic, and degenerative conditions. Stroke is likely the most common cause of aphasia, and it has been estimated that about 20–30% of stroke patients develop aphasia. Almost 800,000 strokes occur in the United States each year, and approximately 2000,000 new cases of aphasia every year are related to stroke. The number of patients with language disorders secondary to traumatic brain injury, brain tumors, and other brain lesions such as arteriovenous malformations is not precisely known. Patients with neurodegenerative disorders such as Alzheimer disease and frontotemporal dementia frequently manifest language deficits. The prevalence of Alzheimer disease in the United States is approximately 5 million cases.
Aphasia is a condition, not a disease; therefore, it has no attributable mortality rate.
Race
No reliable data exist on the incidence of aphasia in different racial groups. Within disease entities, however, such differences are well known. In stroke, for example, African Americans have almost a twofold higher incidence as compared with whites. In addition, specific types of stroke, such as cerebral hemorrhage, lacunar infarctions, and intracranial artery stenoses, are known to be more common in African Americans than Caucasians. One might therefore surmise that poststroke aphasias would be more common in African Americans.
Not enough data are available to evaluate differences in the incidence and clinical features of aphasia in men and women. Some studies suggest a lower incidence of aphasia in women because they may have more bilaterality of language function. Differences may also exist in aphasia type, with more women than men developing Wernicke aphasia.
Age may be an important factor in recovery. Some studies suggest that recovery from aphasia due to a stroke is less favorable in patients older than age 70 than in younger patients. However, at any age, recovery of various degrees can occur, even at times remote from the brain injury.
There are a number of resources for patient education about aphasia. I would recommend the National Aphasia Association website.
Because patients with aphasia sometimes cannot provide a complete history, the clinical information obtained about the cause may depend on the acumen of those around the patient and the history provided by family members. Medical personnel without neurologic training may misdiagnose aphasia as confusion.
Aphasia develops abruptly in patients with a stroke or head injury. Patients with neurodegenerative diseases or mass lesions may develop aphasia insidiously, over weeks, months, or even years. "Neighborhood signs" suggestive of deficits of adjacent cortical areas, or of fiber tracts running near language areas, should be elicited. These signs include difficulties with vision, especially hemianopia; deficits of motor or sensory function; or related neurobehavioral deficits such as alexia, agraphia, acalculia, or apraxia. Patients should be asked about any indications of subtle seizures, such as staring spells or automatisms, or previous aphasic episodes. Rarely, aphasia is caused by herpes simplex encephalitis, a treatable condition but one that offers only a short window for diagnosis. Clues to the diagnosis include a history of fever, seizures, headache, and behavior changes.
A history of headache, acute or chronic, may also be important to the diagnosis of underlying conditions such as brain tumors or arteriovenous malformations. The patient should be asked about any history of memory impairment or of difficulty performing activities of daily living at home, because language dysfunction may be part of a more generalized neurodegenerative condition such as dementia (especially Alzheimer disease or frontotemporal dementia). The patient's handedness should be recorded, as should a history of hypertension, previous brain hemorrhage, cardiac disease, carotid or intracranial vascular disease, or cerebral amyloid angiopathy (a cause of lobar intracerebral hemorrhage in older patients).
Although all of the syndromes described later in this section have clinical and historical validity, they also have numerous limitations.
One-to-one mapping of lesions to deficits is often difficult. Many parts of both hemispheres contribute to the production and comprehension of speech. Individual differences also confuse the correlation of structure with function.
Patients who have had a stroke may evolve from one type of aphasia to another as they recover. The time of evaluation of the patient is therefore important in the syndrome diagnosis.
Patients with slowly growing tumors may have mild aphasia because the lesions grow slowly, allowing adjacent tissues to compensate for functional deficits.
In patients with severe congenital abnormalities, symptoms may develop in an anomalous fashion, and they have mild or no aphasia. Factors affecting the severity of findings include handedness, initial severity of the illness, time since onset, etiology, nature of the underlying vascular lesion (if any), and the patient's age. Patients with severe, left hemisphere injury at a young age may have no residual language deficits.
The status of the contralateral hemisphere is also important for diagnosis and for estimating prognosis for recovery.
Many specific aphasic syndromes have been reported. Classic nosology of the perisylvian aphasias includes Broca, Wernicke, conduction, and global aphasias. The nonperisylvian aphasias include anomic, transcortical motor, transcortical sensory, and mixed transcortical, sometimes called the isolation of the speech area syndrome. Other more specific language syndromes include aphemia, alexia with and without agraphia, and pure word deafness. Subcortical aphasia syndromes are defined more by the anatomy of the lesion than by the language characteristics. These syndromes are discussed in this article.
The syndromes are broad phenotypes that may accompany different types of brain dysfunction, but they are useful because they provide a terminology to permit clinicians to communicate with one another regarding the patient. The presentations of the types of aphasia vary and overlap considerably, but recent studies of both stroke patients and of normal subjects undergoing functional brain imaging have supported the general classification of aphasia syndromes and the localizations of specific language functions.
Of the aphasia types mentioned, the most common and most widely appreciated are the cortical aphasias, including Broca, Wernicke, conduction, and global aphasias.
Specific information should be obtained, including the patient's reading and writing ability, the time frame of symptom onset, any word-finding difficulty, and underlying problems (eg, previous stroke, dementia, or chronic memory loss).
Careful assessment of language function with an evaluation of neighborhood signs is important in the diagnosis of the localization and cause of aphasia. Neighborhood signs are often, but not invariably, seen; they are specific to the individual aphasic syndromes and are a great help in localization.
Although bedside examination can usually reveal the type of aphasia, formal cognitive testing by a neuropsychologist or speech/language therapist may be important to determine fine levels of dysfunction, to plan therapy, and to assess the patient's potential for recovery. Neuropsychologists and speech/language therapists commonly administer language testing batteries, including the Boston Diagnostic Aphasia Examination, the Western Aphasia Battery, the Boston Naming Test, the Token Test, and the Action Naming Test.
This assessment must be broad enough to detect subtle disorders of language in patients in whom aphasia is suspected. Each component of language should be tested individually and thoroughly. Components of bedside language examination include assessments of spontaneous speech, naming, repetition, comprehension, reading, and writing.
Spontaneous speech should be assessed for fluency (ease and rapidity of producing words), amount of speech (number of words produced), initiation of speech, the presence of spontaneous paraphasic errors (semantic or phonemic), word-finding pauses, hesitations or circumlocutions, and prosody. Semantic or verbal paraphasias are substitutions of incorrect words (eg, "fork" for "spoon"), whereas phonemic or literal paraphasias are substitution of incorrect sounds or phonemes (eg, "poon" for "spoon"). These aspects of expressive language are helpful in the diagnosis of aphasia. Dysarthria (consistent mispronunciation of phonemes), apraxia of speech (inconsistent phoneme errors, often at the beginning of a word), and abnormalities of prosody (the emotional intonation of speech, often abnormal with right hemisphere disorders) should also be noted.
Some patients initially perform well during the beginning of an examination, and a deficit becomes apparent only with prolonged testing. Hence, a cursory examination, as in a surgeon's progress note, may be inadequate to detect aphasia.
Confrontation naming is tested with several items involving objects (ring, pen, watch, glasses, paper clip), object parts (watchband, winding stem, crystal), body parts (thumb, palm of the hand, wrist, elbow), and colors. Some naming disorders are particular to the class of items. For example, patients with Broca aphasia and frontal lobe lesions often have more problems with verb naming, and those with temporal lobe lesions and Wernicke or anomic aphasia have more difficulty with noun naming.[1]
The letter-fluency task requires the patient to generate words beginning with particular letters—as many as possible in 1 minute. Often the letters F, A, or S are used because good normal values for these letters are available. A similar test is the animal naming test of the Boston Diagnostic Aphasia Examination, in which the patient is asked to produce as many animal names as possible in 1 minute. The result of such tests may be considered a measure of frontal lobe function but not language function; however, the outcome may provide a rough measure of the number of words spoken spontaneously.
The production of fewer than 8 words beginning with the letter F in 1 minute, excluding proper names and their derivatives, is abnormal in adult native English speakers. Abnormality signifies frontal dysfunction, and aphasia may or may not be present. This test result is often abnormal in dementing illnesses or among patients with frontal dysfunction of any etiology. Category fluency such as animal or fruit naming in one minute also has well-established normal values and is less precisely a measure of frontal lobe function than is letter fluency. Category fluency tends to be more affected in Alzheimer disease.
For some rare syndromes, patients should be tested with objects presented both in the visual and tactile modalities. In a condition called optic aphasia (originally described by Freud), patients cannot name objects presented visually, especially on cards, but their performance improves when the items are presented as real objects that may be palpated, or if the definition of the object is given.
Complete assessment of language production should include oral and written modalities. A patient who can point to the object (a real object or a picture of it from among choices) or who can write the name of the object if he or she cannot say it might be said to have an inability to access the lexical form (ie, a retrieval deficit) but not a complete loss of semantic information about the object.
Assessment should indicate repetition testing. Abnormal repetition is the hallmark of the perisylvian aphasias, the classic aphasias associated with lesions near the Sylvian fissure. Perisylvian aphasias include Broca, Wernicke, conduction, and global aphasias. Preservation of repetition is a major distinguishing feature in nonperisylvian aphasias, including anomic aphasia, the transcortical aphasias, and some subcortical or thalamic aphasias.
Comprehension should be assessed in the oral and written modalities, with both simple and grammatically complex items and with sentences containing at least 2 clauses. Asking patients to perform 1- and 2-part commands is an adequate means to assess comprehension.
Reading should always be assessed as part of language examination. Patients with alexia with agraphia and alexia without agraphia have different anatomic lesions, the former associated with left parietal lesions, the latter with left occipital lesions, usually a stroke in the left posterior cerebral artery territory. Spelling aloud, writing, and spelling words aloud to the patient are all preserved in patients with alexia without agraphia, but not in alexia with agraphia.
Assessing a patient with phonologically regular but complex words (eg, "furniture") and irregular words (eg, "yacht") can be useful to determine if a preexisting dyslexia is present, and, occasionally, whether or not an unusual aphasia syndrome (deep vs surface alexia) is present.
Writing should be assessed for quality, spelling, grammar, and quantity, as well as for the accuracy of the productions. In addition, patients should be tested for apraxia. Apraxia refers to the inability to understand or use tools (such as a pencil or pen) correctly in the absence of a primary motor deficit, and can occur in patients with or without aphasia. Thus, apractic agraphia should be differentiated from aphasic agraphia.
The patient's performance should be interpreted in light of the entire mental status examination. The types of errors, such as omission of functor words (eg, a, the) and telegraphic writing or speech (see Broca aphasia below) should be noted. Patients may be unable to read because of nonlinguistic cognitive dysfunction. For example, in neglect dyslexia, which is usually due to a right hemispheric lesion, patients may fail to attend to and read or write the left side of a word or sentence.
Silent reading may be more effective than oral reading and can be deduced by means of comprehension tests. This condition is common in patients with conduction aphasia and occasionally occurs in patients with Wernicke aphasia.
Broca aphasia
This aphasia syndrome contains a number of distinct components that occur in various combinations. In the complete syndrome, patients present with a nonfluent aphasia. They speak haltingly, without intonation, and have difficulty producing spontaneous speech, naming, and repeating. They may initially be mute, and their articulation may be impaired. Patients are often hypophonic. Comprehension is relatively spared, though it is not normal, especially for complex sentences. Phrases are short and may be telegraphic or agrammatic, including major nouns and verbs but no functor words (articles, adjectives, adverbs, or conjunctions). Patients have telegraphic speech, also called agrammatism. Naming of actions is typically worse than naming of objects.
A writing deficit usually parallels the phonologic deficit.
Repetition is abnormal and often consists of omission of functor words. Patients almost always have syntactic and comprehension deficits. Comprehension of passive constructions and of complex syntactic constructions, such as dependent clauses, may be abnormal. Neighborhood signs include buccofacial or limb apraxia and right hemiparesis, often involving the face and arm more than the leg.
Buccofacial apraxia can be tested by asking the patient to pantomime blowing a kiss or blowing out a match. Speech therapists may observe oral apraxia and difficulty swallowing. Limb apraxia may also accompany Broca aphasia, but it is most commonly caused by a large lesion including additional areas in the parietal or frontal lobes. Depression is extremely frequent because patients are typically aware of their deficits; in extreme form, this is associated with a complete withdrawal, termed by Kurt Goldstein the catastrophic reaction.
Reading is often more affected than auditory comprehension. Patients may make semantic errors (eg, reading "symphony" when the word is "concert"), one of the components of deep dyslexia. Patients may lose the ability to sound out words (they can no longer map graphemes to phonemes) but may be able to read frequent, previously learned, highly imageable words by recognition (they could read "tree" but not "proscription").
Typically, the lesions in Broca aphasia are localized to the dorsolateral frontal cortex (the posterior two thirds of the inferior frontal gyrus operculum), though some cases have associated lesions in the anterior parietal cortex and lateral striate and periventricular white matter. Frontal subcortical connections, such as the subcallosal fasciculus, are important for speech initiation and may disrupt thalamofrontocortical connections. Alexander et al. argued that the full syndrome would not occur without involvement of the underlying white matter tracts.[2]
Mohr et al. found that damage to th etraditional left frontal Broca's areas produced only transient nonfluent aphasia. Patients with lasting Broca's aphasia had larger lesions occupying much of the left frontal operculum and extending even into the parietal lobe.[3]
Kreisler et al. have attempted to relate specific components of the common aphasia syndromes with neurologic localization. The authors investigated 107 patients with a standard aphasia battery and looked at 69 predetermined areas of interest. They found an analysis to identify 67–94% of patients. They found the following:[4]
Note that these localizations largely confirm teachings about aphasia that have been in circulation since the writings of Broca and Wernicke, and others, in the 19th century.
Studies involving functional imaging, including positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) suggest that separate modules within the left inferior frontal gyrus subserve different aspects of speech, including semantic, syntactic, and phonologic functions. Complete Broca aphasia syndrome occurs with a large lesion destructive of the whole area, whereas partial syndromes occur with smaller lesions. As Mohr pointed out, patients with large left perisylvian lesions often have global aphasia in the early days and weeks after their strokes, and they slowly evolve into Broca aphasia. Patients with lesions more limited to the traditional Broca area and a small amount of surrounding frontal tissue may have Broca aphasia on the first day of their stroke. These patients typically recover well. On the receptive side, comprehension of complex sentences with embedded clauses requires activation of the left frontal cortex of the Broca area, and this task is usually deficient in patients with Broca aphasia.[3]
Recovery from Broca aphasia, related to the larger lesion, may occur over months and sometimes years. Patients may progress in the nosology of Broca aphasia and may develop anomic aphasia or become normal over time.
Broca area aphasia, also called a baby-Broca lesion, occurs with a lesion limited to area 44 (the frontal operculum). This aphasia includes what has been called aphemia, cortical dumbness, anarthria, and subcortical motor aphasia. The condition is also closely tied to what speech/language pathologists call apraxia of speech. This condition affects production of phonemes, especially multiconsonant words, and may not represent a true language disorder or aphasia. Aphemia often improves rapidly. A similar syndrome can occur with a lesion limited to the lower prerolandic fissure. Patients may be mute, or they may express themselves in slow, effortful productions, with normal or nearly normal language and syntax. Foreign-accent syndrome is a variant of aphemia, involving damage to the motor speech outflow mechanism. Foreign accent syndrome is more of a cortical dysarthria, akin to acquired stuttering, than a true aphasia.
Wernicke aphasia
Patients with Wernicke aphasia have fluent language expression, but their speech sounds empty and does not convey meaning. There may be fluent phrases without nouns and verbs, containing nonexistent word forms (neologisms). The patient's speech and writing may include paraphasic errors with sound substitutions (phonemic paraphasias), word substitutions (semantic paraphasias), hesitations, pauses, and circumlocutions. Grammar is better preserved than it is in Broca aphasia. This abnormal speech output is called paragrammatic, as compared to the agrammatic output of Broca aphasia.
Naming and repetition are typically impaired, but the most significant problem is the abnormal language comprehension. Although reading impairment often parallels the auditory comprehension deficit, patients occasionally have preserved oral reading or even reading comprehension. This is important in establishing communication with the patient. Written expression is abnormal; unlike patients with Broca aphasia, these patients can write fluently, but their word choice and spelling are usually very abnormal. In mild Wernicke aphasia, abnormal spelling in written productions may be a clue to the deficit. In acute stroke with Wernicke aphasia, patients may seem confused in addition to their language deficits, and they may even appear psychotic.
Patients with Wernicke aphasia are not always aware of their deficits, and over time they may become frustrated that others do not understand them. Some patients become overtly paranoid about their failure to communicate. Patients with Wernicke aphasia may recognize their errors if the mistakes are presented to them offline (eg, on an audio tape).
The lesion is variable but usually involves the posterior one-third of the superior temporal gyrus. Involvement of deep temporal white matter, the middle or inferior temporal gyri, or the inferior parietal lobule may predict a lesser degree of recovery. Wernicke aphasia is most typically associated with embolic strokes affecting the inferior division of the middle cerebral artery, supplying the temporal cortex and sparing the frontal, motor cortex.
In studies by Naeser and colleagues,[5] destruction of Wernicke area predicted lasting loss of comprehension, and recent, acute studies by Hillis and colleagues[6] have found single word comprehension deficits to correlate with hypoperfusion of Wernicke area. Recovery also depends on the size of the lesion, the amount of the traditional Wernicke area that is destroyed, the age of the patient, and the status of the contralateral hemisphere. Recovery can be complete or the aphasia can progress to conduction or anomic aphasia. Binder, however, has presented evidence that the traditional Wernicke area in the superior temporal gyrus is not the source of Wernicke aphasia. It has more to do with phonemic representations, and damage to this area might cause more typical conduction aphasia (see below). Binder suggests that comprehension is subserved by a wider network, including more anterior temporal regions.[7, 8] An article by Bonilha and colleagues has also suggested that wider areas of the temporal lobe are involved in comprehension of words.[9]
Similar or identical lesions can produce different syndromes of aphasia at different points in the disease process. Neighborhood signs should be sought to help in localization. In Wernicke aphasia, neighborhood signs include a superior quadrantanopsia due to involvement of optic radiations, limb apraxia due to involvement of the inferior parietal lobule or its connections to the premotor cortices, finger agnosia, acalculia, or agraphia (components of the Gerstmann syndrome) due to involvement of the angular gyrus. The key neighborhood sign is a negative one; patients with Wernicke aphasia usually have no hemiparesis.
Research has debated the category specificity of semantic, naming, and language deficits.[10] For example, lesions of the fusiform or occipital gyrus may be more likely to cause an inability to name living things or highly imageable words, perhaps due to the proximity to the visual areas. Lesions of the temporal lobes are more likely to affect the naming of tools or inanimate objects, whereas frontal lesions may specifically impair verb naming.
Conduction aphasia
This classical aphasia type is less common than Broca, Wernicke, or global aphasia. Language output is fluent, though some patients make phonemic errors in speech and pause to correct them, giving the speech a somewhat halting quality. This attempt to correct errors is called conduit d'approche. Naming may or may not be impaired. Repetition impairment is the hallmark of conduction aphasia. Auditory comprehension is typically preserved. Careful studies have shown the ability of patients with aphasia to correct their tape-recorded speech, suggesting an offline ability to monitor output in some cases. Oral reading and writing abilities are variable. Patients with conduction aphasia may have normal comprehension of written language; cases of patients with conduction aphasia who are able to read novels have been reported.
The classic disconnection hypothesis, originally formulated by Wernicke and later adopted by Geschwind,[10] implies that both Wernicke and Broca areas were intact, but the connections between them, in the arcuate fasciculus, were disrupted. By this theory, a disconnection between these centers results in the inability to repeat, in the setting of intact comprehension and verbal fluency. Other theories of conduction aphasia include a deficit of auditory-verbal short-term (immediate) memory or “inner speech.”
The supramarginal gyrus is often affected in conduction aphasia, though disruption of the subcortical connections in the arcuate fasciculus may also be important. Research has implicated the supramarginal gyrus in the decoding of phonemes in receptive language and presumably their translation into oral expression. Recovery is usually good, but residual semantic and phonologic difficulties may remain. Kreisler et al., in the work cited, could not confirm the roles of the arcuate fasciculus or supramarginal gyrus as classically described.[4]
Neighborhood signs in conduction aphasia include superior quadrantanopsia, if the lesion undercuts the parietal lobe, and limb apraxia, which is typically more disabling and less often diagnosed than the aphasia itself. Temporal lobe lesions that do not totally damage the Wernicke area may result in conduction aphasia, and such cases do not have associated apraxia, whereas patients with left parietal lesions often have associated limb apraxia.
Global aphasia
In this type of aphasia, the patient has deficits in all aspects of language: spontaneous speech, naming, repetition, auditory comprehension, reading, and writing. The deficits need not be total. Global aphasia may result from strokes, tumors, dementia, or other causes.
Global aphasia is commonly seen in patients with large infarctions of the left cerebral hemisphere, typically involving the occlusion of the internal carotid or middle cerebral artery and resulting in a large, wedge-shaped infarction of the frontal, temporal, and parietal, often including deep portions of the middle cerebral artery territory. Right hemiplegia (face and arm worse than the leg) is the rule, as is right homonymous hemianopsia. Limb apraxia is common. Some patients have a catastrophic reaction, described by Kurt Goldstein as an emotional meltdown when the patient is asked to perform language tasks; this phenomenon is likely related to depression.
Global aphasia rarely occurs with right hemispheric lesions (also called crossed aphasia). About one fifth of left-handed people and 1% of right-handed people have global aphasia after mirror-image lesions of the homologous cortex of the right hemisphere; in this case, left homonymous hemianopsia and left hemiplegia are expected.
Global aphasia rarely occurs without hemiparesis. In such cases, dual lesions in the left cerebral hemisphere are expected; these spare the motor areas but affect both anterior and posterior perisylvian language areas. Although multiple strokes could produce such a clinical picture, in practice, the possibility of tumors should be considered with such multiple lesions. In cases of aphasia without hemiparesis, a thalamic lesion should also be considered in the differential diagnosis.
Although global aphasia is often considered a devastating injury, gradations of global aphasia exist. Many patients with poststroke global aphasia evolve toward Broca aphasia, or mixed nonfluent aphasia, with improvement in language comprehension over time. Many patients with global aphasia are proficient at making their needs understood without spoken or written speech. Prosody, inflection, pointing, and expressions of approval or disapproval are some of the ways in which patients with global aphasia may communicate successfully.
Patients with large, left hemisphere lesions and global aphasia are vastly different from patients with large, right hemispheric lesions whose language may appear normal but the nonlinguistic aspect of language expression is lost, including the prosody or emotional aspect of language expression and the ability to understand humor or sarcasm in the speech of others. Patients with such right-hemisphere syndromes are less aware of their deficits than patients with aphasia and may be less responsive to rehabilitation.
Factors affecting the prognosis of patients with global aphasia may include the nature of the underlying injury (eg, dementia, tumor, stroke), the age of the patient, the area of infarction (if present), the health of the remaining brain, and the availability of rehabilitation services.
Recovery in the first 6 months generally outpaces later recovery; however, some patients can recover function years after the initial injury. In one study of patients with global aphasia, more improvement occurred during the second 6 months after the injury than during the first 6 months.[11]
Pure word deafness
Patients with pure word deafness cannot comprehend spoken language, but they are not deaf. Their verbal output and reading comprehension are said to be intact, but most published cases have shown some degree of fluent, paraphasic speech.
The condition can occur because of damage to the superior temporal (Heschl) gyrus bilaterally, but cases have been described with unilateral, left temporal lesions. The disconnection theory proposes that inputs from both Heschl gyri are cut off from input into the left hemisphere Wernicke area where sounds are decoded into language.
Pure word deafness should be differentiated from cortical deafness, in which both language and nonlinguistic sounds are affected, and also from auditory nonverbal agnosia. Patients with cortical deafness may appear deaf, but they often have some sparing of pure-tone hearing, especially as recovery occurs. Auditory nonverbal agnosia involves failure of recognition of familiar sounds, such as the moo of a cow or the ringing of a bell. A related disorder is phonagnosia, in which familiar voices are not recognized. All of these cortical auditory deficits (pure word deafness, cortical deafness, auditory nonverbal agnosia, and phonagnosia) usually reflect bilateral temporal lobe lesions.
Transcortical aphasias
The term transcortical aphasia was originally chosen by Lichtheim to indicate aphasias related to primary lesions not involving the language cortex but rather connected areas of the association cortex, which he called the "area of concepts." By definition, patients with transcortical aphasia can repeat, but they have difficulty naming or producing spontaneous speech or understanding spoken speech. Patients with transcortical motor aphasia can comprehend speech but have diminished speech output and an inability to name items. Sometimes they speak only in single words, after a delay, or in a soft voice.
Transcortical motor aphasia involves a deficit in the initiation of speech, reduced phrase length, and abnormal grammar. Mutism may be present initially. Repetition is relatively unimpaired, distinguishing these patients from those with Broca aphasia who cannot repeat fluently. In some patients, a stroke in the anterior cerebral artery territory is the cause; leg greater than arm weakness, shoulder greater than hand weakness, and often an involuntary grasp response are associated findings. Because most strokes with aphasia localize to the middle cerebral artery territory, this anterior cerebral artery deficit is quite distinct, though much less common.
In transcortical sensory aphasia, patients can produce fluent speech, but it is often empty and paraphasic. Patients also have a severe deficit in comprehension of speech. Their naming is often abnormal, and they lose semantic associations of speech. In general, they act much like patients with Wernicke aphasia, except that they can repeat. This type of aphasia is typically seen in advancing Alzheimer disease and other progressive dementias, but it is also seen occasionally in patients with stroke, typically those with bilateral lesions in the parieto-occipital cortex or a lesion in the left temporo-occipital cortex.
Mixed transcortical aphasia, also called the syndrome of isolation of the speech area, involves ability to repeat but not to produce spontaneous speech or comprehend language. Patients may repeat in an echolalic fashion, and they may complete common phrases begun by the examiner. This syndrome resembles global aphasia, except for the preserved repetition. This syndrome can be seen in patients with large watershed infarctions, or occasionally in neurodegenerative conditions such as Alzheimer disease.
Anomic aphasia
Patients with anomic aphasia present with fluent speech, intact or mostly intact repetition, intact auditory comprehension, reading, and writing, but an inability to name objects and body parts. Anomic aphasia may follow recovery from another type of aphasia, but it can also be an initial presentation of an aphasia syndrome, and it warrants its own aphasia syndrome.
Anomic aphasia is less specific in lesion localization than the other syndromes mentioned previously. Anomia may occur with lesions in the dorsolateral frontal cortex, temporal or temporo-occipital cortex, or thalamus. Tumors of the left temporal lobe may present with anomic aphasia. This aphasia type is also the typical language deficit in patients with early Alzheimer disease.
Subcortical aphasias
Broca reported lesions of the deep basal ganglia with cortical lesions in his original autopsy report of his famous patient, Tan-tan. More controversial than that association is whether a basal ganglia lesion by itself can cause aphasia.
A series of reports in the early 1980s, which used computed tomography (CT) as the primary neuroimaging modality, associated lesions of the head of the caudate nucleus, anterior putamen, and anterior limb of the internal capsule with a nonfluent aphasia syndrome, often with dysarthria and with better repetition and comprehension than typically seen with Broca aphasia.[12, 13, 14, 15] This syndrome has been called the anterior subcortical aphasia syndrome. When the lesion extends into the temporal isthmus area, subcortical versions of Wernicke and even global aphasia can occur. The diagnosis of subcortical aphasia is based more on the imaging of a subcortical lesion than on the specific language characteristics of the aphasia syndrome.
In some cases, MRIs have revealed cortical lesions in patients with aphasia whose CT scans demonstrated only subcortical lesions. Blood-flow imaging has shown flow abnormalities in the cortex of patients whose MRIs depicted only lesions in the basal ganglia. Such diminished flow may partly reflect cortical ischemia and partly reflect a reduced perfusion of functionally connected areas called diaschisis.
Weiller et al examined patients with striatocapsular lesions, some with aphasia or neglect, and some without. On MRI, lesions in both groups were similar. However, patients with aphasia and neglect had low blood flow in the cortex, suggesting that cortical ischemia may also be important in some subcortical aphasias. Weiller also found that among patients with identical vascular syndromes, those who had strokes due to atrial fibrillation typically had aphasia and neglect, whereas those who had strokes due to large vessel stenosis did not. They attributed the finding to the ability of patients with chronic low flow due to large vessel stenosis to develop collaterals, whereas those with a sudden occlusion due to an embolus could not do so.[15]
Thalamic aphasias
Thalamic aphasia, like the subcortical aphasia syndromes, is defined by the anatomic documentation of a lesion in the thalamus rather than by the specific language characteristics of the aphasia syndrome. Patients with thalamic aphasia usually present with fluent language disorders, often without hemiparesis. Associated findings include anomia, jargon speech, semantic paraphasic errors, intact repetition, and relatively preserved comprehension. Such patients may also manifest an acute affective syndrome with abulia or severe depression.
Thalamic aphasia was initially described in patients with left thalamic hemorrhage. The author reported a left-handed patient with a right thalamic hemorrhage, indicating that language dominance extends down to thalamic level.[16] In hemorrhage, of course, the language disorder possibly results from mass effect or pressure on adjacent structures rather than on the specific focus of the hemorrhage. More recent cases of thalamic aphasia secondary to ischemic stroke have solidified the evidence that the thalamus is important to language function.
The vascular lesion that affects the anterior thalamus is a small-vessel disease affecting the polar or tuberothalamic artery of the thalamus. The lesion is easily seen on CT scans or MRIs. Lesions in the anterior thalamus also affect memory. Crosson et al. argued persuasively for the importance of pulvinar and other posterior structures in language, but their data were based on stimulation rather than lesion ablation.[17]
Pulvinar strokes causing aphasia are exceedingly rare because of the vascular anatomy of the thalamus. Lesions of the paramedian thalamus (thalamoperforating artery), especially if bilateral (some patients have a single artery, sometimes called the artery of Percheron, supplying both sides), cause deficits in memory and language. Crosson also discusses the possible role of the ventral lateral nucleus in atypical aphasias, but usually this vascular territory (inferolateral arteries) involves a pure sensory stroke, while the posterior choroidal artery territory mainly involves the lateral geniculate body, causing an isolated hemianopia.
Lesions of the white matter between the thalamus and the temporal lobe, the temporal isthmus, or temporal stalk may produce aphasia due to deafferentation of the overlying temporal lobe. These aphasias closely resemble Wernicke aphasia. As mentioned above, however, the cases reported have not entirely excluded cortical involvement or hypometabolism as a cause of the syndrome.
Pure alexia without agraphia
Pure alexia is known by a variety of names, including alexia without agraphia, posterior alexia, and literal or letter-by-letter alexia. Patients with pure alexia have normal expressive speech, normal naming (except in some cases for color anomia or inability to name colors), normal repetition, normal auditory comprehension, and even normal ability to write. Their alexia is a relatively pure deficit. Patients may be able to write a sentence, then be unable to read it. They have no difficulty spelling aloud and no difficulty in recognizing words spelled to them aloud or spelled in tactile fashion on the palm of the hand. Patients may be able to read individual letters, then laboriously piece them together and say the words (letter-by-letter alexia).
Neighborhood signs useful in the diagnosis of pure alexia include a contralateral (right) superior quadrantanopsia or hemianopia and color anomia. The syndrome is almost always associated with a stroke in the territory of the left posterior cerebral artery. The lesion may also involve the splenium of the corpus callosum and the medial temporal lobe.
Dejerine first described this syndrome in 1892, postulating a disconnection between the right occipital cortex (and intact left visual field) and the left hemisphere language area, such that visual information cannot be decoded into language in the left hemisphere.[18] Later contributors recognized that the posterior left hemisphere has a word-form recognition area that, if damaged, prevents patients from reading words at a glance, as normal readers do. Nearly a century later, Geschwind[10] and then Damasio[19] refined the disconnection hypothesis of pure alexia. Cognitive neuropsychologists and behavioral neurologists have recognized the concept of damage to the orthographic recognition areas in the left occipital lobe.
Alexia with agraphia
Alexia with agraphia is also known as the angular gyrus syndrome and central alexia. It is, in effect, an acquired illiteracy; patients lose their previously acquired reading and writing skills. Most lose spelling and the ability to understand words spelled to them. Many patients have fluent, paraphasic speech, unlike the preserved speech of pure alexia without agraphia, but auditory comprehension is much superior to reading comprehension. The lesion usually involves the angular gyrus area in the left inferior parietal lobule. This syndrome was also described by Dejerine.
Closely related to the pure alexia with agraphia syndrome is the Gerstmann syndrome. Gerstmann brought together the 4 deficits of agraphia, acalculia, right-left confusion, and finger agnosia and associated them with lesions of the dominant parietal lobe. Alexia, though not originally a cardinal feature of the Gerstmann syndrome, is often associated.
Modern authors such as Benton have questioned the validity of the Gerstmann syndrome.[20, 21] Some patients may have one or more of the deficits without the others. Stimulation studies in epileptic patients, however, have reproduced combinations of these deficits with stimulation in the angular gyrus area, confirming the association of the key elements of the Gerstmann syndrome.
Right hemisphere language disorders
Right hemisphere contributions to language are numerous, and recent research has led to a better understanding of right hemisphere functions related to communication. The right hemisphere can maintain an extensive vocabulary and read at the word and phrase level. Higher functions of right hemisphere speech, subserved in part by right frontal and temporal lobes, include the comprehension of metaphor, sarcasm, and humor, as well as the emotional prosody of speech, ie, the extralinguistic aspects of human communication.
Patients with right hemisphere lesions may understand words but fail to understand the emotional context of a conversation or the facial expressions and tones of voice that convey meaning in normal communication. In addition, they may fail to observe normal turn-taking and other pragmatic aspects of a conversation. In patients with normal speech and language comprehension, these deficits can be disabling in a social context. Patients with right hemisphere lesions may have a problem with discourse and have difficulty stringing together several sentences into a spoken paragraph with a beginning, middle, and end, as a storyteller or lecturer would do.
Aphasia is a symptom and not a disease; it can occur in a variety of types of brain injury and pathology.
In stroke, the deficit is usually sudden and obvious.
In substantial head trauma, the deficits may be unrecognized. Exceptions involve hemorrhages or traumatic contusions directly disrupting the left hemisphere language cortex, which may then resemble stroke syndromes.
Language disorders in dementia take a variety of forms. In dementia, the language problem may be insidious and may require elicitation with the assistance of an experienced physician, speech/language pathologist, or neuropsychologist. Some dementias present with aphasic syndromes that closely resemble the aphasic stroke syndromes described above, except that they begin gradually and progressively worsen. If aphasia is the sole deficit over a 2-year period, the term primary progressive aphasia can be used, though many of these patients develop other cognitive deficits over time.[22]
Primary progressive aphasia (PPA) has been the subject of a great deal of research in recent years. The aphasia types of PPA have been divided into three separate syndromes. The first is primary nonfluent progressive aphasia, resembling Broca aphasia but progressive. The atrophy is largely inferior frontal, and the pathology is usually related to frontotemporal dementia. Histochemistry is typically a tauopathy. The second type is semantic dementia, in which patients not only have difficulty naming, but word meanings are lost, even for single words. The pathology is often bilateral, in the temporoparietal cortex, and the cause is variable, non-tau and non-Alzheimer disease, often a progranulin disorder. The third type, logopenic primary progressive aphasia, involves prominent anomia and difficulty repeating long phrases. This type often involves the left parietal cortex but can be bilateral, and the underlying pathology is usually Alzheimer disease.[23] In most cases, the associated memory deficits, as well as right hemisphere disorders and frontal dysexecutive syndromes make clear the more widespread nature of the dementing illness.[23, 24] In typical Alzheimer disease, memory is usually the first function to be impaired, and language deteriorates only later. Patients may progress from a pattern of anomia to more severe deficits such as Wernicke or transcortical sensory aphasia, then in late stages to global or mixed transcortical aphasia.[25]
In multiple sclerosis and Parkinson disease, no language abnormality is usually present, though patients with Parkinson disease can develop language deficits along with dementia. The disease corticobasal degeneration often involves a nonfluent aphasia, sometimes meeting criteria for primary progressive aphasia before the motor deficits of limb apraxia and Parkinsonism begin. Dysarthric speech patterns are common in both multiple sclerosis and Parkinson disease.
A rare cause of aphasia in children is the Landau-Kleffner syndrome, a syndrome of acquired epileptic aphasia. Symptoms begin in childhood and progress; electroencephalographic (EEG) findings confirm the diagnosis. The syndrome is treatable; however, in some patients, the seizures are controlled more than the aphasia is.
A rare but important condition not to overlook is herpes simplex encephalitis. The aphasia in herpes simplex encephalitis may mimic Wernicke aphasia mimicking a stroke deficit, but often with associated confusion. The disease usually resents with confusion, fever, headache, and seizures. Over time, the MRI usually shows a classic insula-sparing lesion, involving one or both temporal lobes. Early treatment with antiviral agents is crucial to prevent further injury until the diagnosis can be confirmed, usually by PCR testing of spinal fluid.
Aphasia is diagnosed based on language examination and the localization of a lesion in the left hemisphere. Careful mental status and language examination is always important to diagnosis.
The diagnosis of aphasia is based on physical examination and detailed mental state examination.
Aphasia is a sign as much as it is a clinical problem. Therefore, the laboratory tests required depend on the underlying pathophysiology.
Neuroimaging is required to localize and diagnose the cause of aphasia. CT scanning and MRI are the mainstays of neuroimaging.
CT effectively demonstrates acute bleeds and most ischemic strokes older than 48 hours; however, it may miss strokes less than 48 hours old.
MRI with diffusion-weighted imaging detects strokes as early as an hour after onset. New imaging sequences such as the T2* or gradient echo imaging are sensitive to detect hemorrhage, an early limitation of MRI technology.
Contrast enhancement may be required to demonstrate tumors by both CT and MRI.
Thin sections through the temporal lobes can demonstrate hippocampal atrophy or sclerosis, which are common in epilepsy and dementia. Coronal imaging on MRI is especially helpful in the detection of asymmetric hippocampal atrophy.
At a time when gross atrophy of the tissue is hard to detect, PET and SPECT may be helpful in detecting hypometabolism or reduced cerebral blood flow, respectively, in dementing illnesses. These techniques are also useful in localization of epileptic foci.
Functional MRI is increasingly being used in the study of normal activation of language structures in healthy subjects. In research studies, these techniques have also proven useful in elucidating patterns of recovery after neurologic injury such as a stroke with aphasia. While early research indicated that homologous areas of the right hemisphere might subserve language recovery, recent studies have shown that activation of adjacent left hemisphere cortex is associated with more complete recovery of language function.[26]
EEG is important in patients with suspected seizures.
Neuropsychological testing and speech therapy evaluation are helpful for guiding therapy for aphasia.
The treatment of a patient with aphasia depends on the cause of the aphasia syndrome. Acute stroke treatment for the aphasic patient, such as intravenous tPA, intra-arterial interventional treatments now called mechanical thrombectomy, carotid endarterectomy and stenting, or even blood pressure manipulation may help to alleviate the deficit. Surgery for a subdural hematoma or brain tumor may be beneficial. In infections such as herpes simplex encephalitis, antiviral therapy may help the patient recover.
Speech and language therapy is the mainstay of care for patients with aphasia. The timing and nature of the interventions for aphasia vary widely. Blinded studies are limited, and recovery of some degree is the norm, but several studies have indicated that speech and language therapy does improve clinical outcomes in patients with aphasia. Patients' difficulties vary, and individualized programs are often important.
Consultations with a speech and language therapist and a neuropsychologist may prove helpful.
Recent studies have shown that intense treatment with a speech and language therapist, several hours per day several days a week, is more effective than a similar number of shorter sessions spread out over a longer period.
The prognosis for life in a patient with aphasia depends on the cause of the aphasia. A left hemisphere glioblastoma may be associated with a very short life expectancy, whereas a minor stroke may have an excellent prognosis. It is the underlying pathology, not the aphasia itself, that determines prognosis.
The prognosis for language recovery varies depending on the size and nature of the lesion and the age and overall health of the patient. Most patients, even elderly ones, experience some recovery in poststroke aphasia, and some recover completely. In general, patients with preserved receptive language functions are better candidates for rehabilitation than are those with impaired comprehension. The potential for functional recovery from primarily expressive aphasia such as Broca’s aphasia after a stroke is excellent. The potential for recovery from a Wernicke aphasia due to a stroke is not as good as that for Broca aphasia, but most of these patients show some recovery. The potential for recovery from aphasia due to an untreatable tumor or neurodegenerative disease is poor.
The prognosis for the patient to become independent is subtly different than that for language recovery. Patients may recover functionally and be able to live independently in spite of having a persisting aphasia, as long as they do not have other concomitant deficits such as dementia or loss of the ability to use household tools (apraxia), often related to inferior parietal lobule or frontal involvement or other cognitive deficits.
Although it was once taught that most improvement from aphasia occurs in the first six months after a stroke, most now acknowledge that recovery can occur many months or even years after the initial stroke that caused the impairment. In severe, global aphasia, there may actually be more improvement in the second 6 months after the stroke than in the first 6 months.[10]
Family members may benefit from education regarding language impairment to care for affected patients.
The National Aphasia Association provides a variety of educational materials.