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Nestor Galvez-Jimenez, MD, MSc,
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Selim R Benbadis, MD,
Professor, Director of Comprehensive Epilepsy
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Hospital
Parkinson disease is a slowly progressive, degenerative neurological illness which most commonly affects middle-aged and elderly individuals. Although easily recognizable when the disease is established, mild or incipient Parkinson disease may be difficult to recognize, particularly in young individuals, and may be overlooked for several months or years.
Young-adult Parkinson disease, which is defined as symptom onset before age 40 years is unusual and juvenile parkinsonism, with onset before age 21, is extremely rare.
In young patients, dopa responsive dystonia should be seriously considered as an alternative diagnosis. Dopa-responsive dystonia usually starts as a gait disorder resulting from lower extremity dystonia, but it can also be accompanied by bradykinesia. Symptoms may exhibit substantial diurnal variation and usually respond dramatically to low doses of levodopa, with a sustained benefit and without the emergence of dyskinesia. The clinical spectrum of dopa responsive dystonia is wide, though, and distinction between Parkinson's disease and dopa responsive dystonia on a clinical basis or by age of onset is not infallible.
Patients with young-onset Parkinson disease have symptoms that are similar to those of older patients but have a higher incidence of dystonia, particularly in the lower extremities. Because dystonia as an isolated symptom of other diseases is unusual, early Parkinson disease should be suspected in middle-aged individuals with an isolated dystonia in the lower extremity.
For more information, see Medscape's Parkinson's Disease Resource Center.
Pathologically, Parkinson disease is associated with loss of dopaminergic neurons in the substantia nigra and dopamine deficiency in the striatum. This results in abnormally increased activity of the subthalamic nucleus and internal segment of the globus pallidus, which cause the motor manifestations of the disease. In Parkinson disease, other nondopaminergic neurons also are affected, resulting in a milder deficiency of the other monoamine neurotransmitters, including serotonin and norepinephrine. In concert with dopamine deficiency, depletion of these other neurotransmitters results in psychological and behavioral symptoms, including depression, asthenia, memory and concentration difficulties, and sleep disturbances. Involvement of the intermediolateral cells in the thoracic spinal cord, autonomic ganglia, and autonomic neurons in the wall of the abdominal viscera also occurs in Parkinson disease and results in dysautonomia.
Juvenile and young-onset parkinsonism may include patients with several different pathologies and is clinically heterogeneous, both in symptoms and in response to levodopa. As discussed under Causes, juvenile parkinsonism is classically an autosomal recessive inherited condition and is associated in some families with a mutation in the gene coding for the protein parkin; other recessive gene mutations have been also discovered in families with young-onset parkinsonism.[1, 2] Heterozygous mutations in the parkin gene may increase susceptibility for early-onset disease as well.[3]
In contrast to Parkinson disease and juvenile parkinsonism, dopa-responsive dystonia is not a degenerative illness, nor is it associated with loss of dopaminergic neurons. It is most commonly due to mutations in GTP cyclohydrolase I, an enzyme involved in the activation of tyrosine hydroxylase, the rate-limiting enzyme involved in dopamine synthesis.[4] This condition is described in further detail in the eMedicine article Dopamine-Responsive Dystonia.
The overall prevalence of Parkinson disease is estimated at 0.2% but rises with age, affecting as many as 0.5-2% of individuals older than 70 years. The prevalence has been estimated as 25-50 cases per 100,000 population in individuals younger than 50 years, affecting as many as 100,000 patients in the United States, and approximately 5 cases per 100,000 individuals younger than 40 years.
International
Parkinson disease is found worldwide but is generally more prevalent in Western countries than in Asia or Africa.[5, 6]
Mortality/Morbidity
Prior to the discovery of levodopa, Parkinson disease was associated with a significant mortality rate and shortened life span; the average life expectancy of patients was approximately 10 years after diagnosis. In the latter stages, patients with advanced Parkinson disease were restricted to a wheelchair or bed and died of complications of immobilization, such as aspiration pneumonia, urosepsis, or infected decubiti. Since the development of levodopa and other drugs, the life spans of patients are normal, or nearly so.
However, a number of signs and symptoms that were rare prior to the discovery of levodopa now are common. These include dementia, adverse mental effects of drug treatment such as hallucinations and psychosis, severe dysarthria, dysphagia, aspiration, and falls and fractures as a result of postural instability and freezing.
Younger individuals with Parkinson disease have different problems. Troublesome motor fluctuations and dyskinesias are especially common and may occur within several years of the initial symptoms. Severe dysautonomia, freezing, and dementia are less common than in elderly patients but may develop after many years of disease. Painful dystonia during periods of recurrent parkinsonism ("off" dystonia) is a particularly distressing and common motor symptom. In some patients, a nonfluctuating and fixed dystonia may develop and require bracing or surgical correction.
Race
Parkinson disease affects all races.
Race and geographical factors are associated with differences in the incidence and prevalence of Parkinson disease. In a study of members of a health maintenance organization in California, the incidence of Parkinson disease was highest in Hispanics, followed by non-Hispanic whites, Asians, and blacks.[7] It has also been observed that the prevalence of Parkinson disease in blacks living in the United States is much higher than blacks living in Nigeria, and a similar difference has been reported comparing the prevalence of Parkinson disease in urban dwelling individuals in China compared to rural inhabitants.[5]
Juvenile parkinsonism due to the parkin mutation is described as accounting for more cases of juvenile parkinsonism in Japan than in other countries. However, more recent studies in other countries have also shown a large fraction of young adults (>40 y) as having the parkin mutation.
Sex
Parkinson's disease affects both sexes but is more prevalent in males, affecting approximately 1.5-2 times as many men than women.[7]
Although the disease is similar overall in both sexes, one study found that women more often presented with tremor (67%) than men (48%).[8]
Age
Parkinson disease is more common with advancing age. It affects as many as 1.5% of individuals older than 65 years and as many as 3.5% of individuals older than 85 years.[9]
Parkinson disease is unusual in individuals younger than 50 years, with prevalence rates ranging from 0-46 cases per 100,000 population, averaging 27 case per 100,000 population among studies. It is still rarer in individuals younger than 40 years, with most studies reporting fewer than 5 cases per 100,000 population. In some referral populations, however, as many as 10% of patients with Parkinson disease report disease onset before 40 years.
Approximately 10,000-15,000 individuals 40 years and younger in the United States have Parkinson disease. This is nearly half of the estimated total number of individuals of all ages in the United States with amyotrophic lateral sclerosis (ALS).
Diagnosis of Parkinson disease in young patients is similar to that in elderly patients and is based on finding a combination of tremor, rigidity, bradykinesia, and postural instability. The symptoms may, however, be vague and difficult to pinpoint or to date accurately and may include fatigue, malaise, myalgias, mild incoordination, depression, and other less well-defined complaints. The initial symptoms typically start insidiously and emerge slowly over weeks or months. This slow progressive pattern is characteristic of the disorder. In fact, other patterns, such as a stable, waxing and waning course over many months, or the abrupt appearance of various signs or symptoms, are unusual and should raise concerns about the diagnosis.
Juvenile parkinsonism (onset before age 21) and dopa-responsive dystonia usually begin with dystonia affecting the lower extremities. However, these 2 conditions overlap considerably, and exceptions have been identified by genetic testing. Patients with sporadic Parkinson disease with typical symptoms and onset in middle age have rarely been found to have a mutation in the same gene, parkin, that results in juvenile parkinsonism. Patients with the clinical picture of dopa-responsive dystonia also have demonstrated this mutation.
Tremor
Tremor is the most common initial symptom, occurring in approximately 70% of patients. It usually is described by patients as shakiness or nervousness. It may vary considerably, emerging only with stress, anxiety, or fatigue, or it may occur only when supporting weight with the affected limb, such as experiencing arm tremor when getting out of a low chair.
Most commonly, tremor affects the upper extremity. It generally begins in the fingers or thumb, but also can start in the forearm or wrist. A very common pattern is for the tremor to begin in the upper extremity, spreading to the ipsilateral lower extremity or the contralateral upper extremity before becoming more generalized. Although Parkinson disease is a rare cause of tremor affecting the head or neck, chin or lip tremors are seen occasionally, usually ipsilateral to the extremity tremor. Most classically, the tremor of Parkinson disease disappears with action or usage of the limb, but this is not seen in all patients.
Bradykinesia
Symptoms of bradykinesia are more varied than those of tremor. These may include a feeling of weakness, without true weakness found on physical examination; loss of dexterity, sometimes described by patients as the "message not getting to the limb"; fatigability; or aching when performing repeated actions.
Facial bradykinesia is characterized by depression or fatigue. The speech may become softer, less distinct, or more monotonous. In more advanced cases, speech is slurred, poorly articulated, and difficult to understand. Drooling is an uncommon initial symptom in isolation but is reported commonly in patients with mild disease.
Truncal bradykinesia results in slowness or difficulty in rising from a chair, turning in bed, or walking. If walking is affected, patients may limp, take smaller steps, or be transiently unable to move. This "freezing" is seen commonly in patients with more advanced disease; it is more prominent in doorways or narrow areas, and can result in patients getting trapped behind furniture or being unable to cross a door threshold easily.
In the upper extremities, bradykinesia can cause small effortful handwriting (ie, micrographia) and difficulty using the hand for fine dexterous activities such as using a key or kitchen utensils. In the lower extremity, unilateral bradykinesia commonly causes limping, which occasionally can be an initial symptom.
Rigidity
Though a common physical sign of Parkinson disease, rigidity is a less common symptom in patients with early onset of the disease.
Some patients may describe stiffness in the limbs but this may reflect bradykinesia more than rigidity.
Occasionally, individuals may describe a feeling of ratchety stiffness when moving a limb, which may be a manifestation of cogwheel rigidity.
Other initial symptoms include regional pain, variously described as coldness, tingling, cramping, or aching; depression or anhedonia; slowness in thinking and speaking; a general feeling of weakness, malaise, or lassitude; and a number of dysautonomic symptoms, including constipation.
In young patients, dystonia is a common initial symptom, producing cramping or aching and a tendency of the extremity (usually the foot) to turn in or the great toe to dorsiflex. Common dystonic symptoms include curling, inversion, or plantar flexion of the foot, and adduction of the arm and elbow, causing the hand to rest in front of the abdomen or chest. These dystonic postures can wax and wane, occurring with fatigue or exertion.
The principal manifestations of Parkinson disease are tremor, rigidity, bradykinesia, and changes in gait and posture.
Tremor is, most typically, a resting tremor that is reduced or eliminated with limb movement. It is seen commonly in the upper extremities during walking and can be seen more obviously by asking the patient to perform rapid movements with the contralateral limb (eg, rapidly clenching and unclenching a fist). A minority of patients may have an action or sustention tremor, best seen by holding the arm outstretched.
Rigidity
Rigidity may be either "lead-pipe" or cogwheeling; it may be present in the limbs and is frequently asymmetric. The degree of rigidity varies widely and does not correlate well with tremor or bradykinesia. It commonly is abolished or reduced by levodopa or dopamine agonists and is frequently minimally present or absent in patients on long-term drug treatment. It is best recognized by passively moving a limb in 2 or more planes, such as simultaneously flexing and extending the elbow while supinating and pronating the forearm.
Rigidity also can be detected by passively moving one limb while the patient simultaneously moves the contralateral limb, such as drawing an imaginary circle in the air. However, a mild increase in tone is observed normally with this maneuver in healthy individuals; mild rigidity, in the absence of other signs, should be interpreted with caution.
Bradykinesia
Bradykinesia is seen as a paucity or slowness of movement. In the limbs, this results in a reduction in the amplitude and speed of movement. It is best recognized by having the patient tap the index finger against the thumb, supinate and pronate the forearm in the air, clench and unclench a fist, or tap the heel or the toes against the ground. When more severe, it may be difficult for a patient to initiate and maintain a movement, producing functional weakness; however, on direct motor testing and with encouragement, little or no weakness is observed.
Handwriting changes, particularly micrographia, are a frequent manifestation, and are a sensitive sign of incipient Parkinson disease in many patients; mild micrographia is sometimes noticeable by comparing old and recent signatures on credit cards. Bradykinesia also can result in changes in facial expression, causing reduced blinking and smiling. Myerson sign (blinking when the glabella is tapped repeatedly) is observed commonly but is nonspecific.
Speech and swallowing may be affected. The speech may be slightly softer, muffled, and less distinct. In more severe disease, the speech is rapid, monotonous, and slurred. Palilalia, repeating the initial syllable of a word similar to stuttering, also can occur in patients with more advanced disease and can be a side effect of medications. Sialorrhea and dysphagia are common problems in patients with more advanced disease.
Changes in gait, posture, and balance are frequent manifestations of Parkinson disease. Initial gait changes may include limping and reduced or absent arm swing. As the disease worsens, patients may have en bloc turning (ie, lack of truncal rotation when turning), festination (ie, a short-stepped, propulsive gait, as if falling forward), or freezing (ie, transient inability to move the legs, commonly seen in doorways or in narrow quarters). Freezing also can be noticeable as a subtle hesitancy in initiating walking after standing or after turning directions.
The posture may become more flexed, sometimes to extreme levels. Postural stability is affected, producing retropulsion. This is sometimes obvious without provocation and can be recognized by standing behind the patient and pulling the upper trunk backwards at the shoulders. Scoliosis, usually away from the more affected side, is seen occasionally.
Dystonia is recognized most commonly in the lower extremities, causing an equinovarus posturing in the foot and ankle and curling of the toes. In the upper extremities, the arm is held adducted against the chest and flexed at the wrist; when severe, the hand may be held in a fist and the palm may become macerated or thickened.
Few other neurological manifestations are noted in patients with Parkinson disease; pyramidal signs, ophthalmoplegia, anisocoria, cerebellar ataxia, or severe dysautonomia at symptom onset is atypical and usually suggests an alternative diagnosis. Reflex asymmetries may be observed occasionally, typically causing a mild degree of hyperreflexia ipsilateral to the more affected side. Spontaneous dorsiflexion of the great toe (the "striatal" toe) also is seen.
Although cognition and mood are affected in many patients with Parkinson disease, findings of the office mental status examination are normal in most patients. Signs of higher cortical dysfunction, such as neglect, agnosia, dysphasia, apraxia, or severe memory disturbances, are not observed in patients with idiopathic Parkinson disease, with the exception of patients in whom Lewy body dementia develops late in the disease course; it is very rare in younger patients.
The etiology of Parkinson disease is largely unknown in most patients. However, evidence does exist for both genetic and environmental causes. In the United States, rural residence, exposure to well water, and prior use of pesticides are environmental factors that have been found to be associated with an increased risk of developing Parkinson disease.
Genetic factors also may be important in the pathogenesis of the disease. A positive family history is found in approximately 15-20% of patients with idiopathic Parkinson disease, but the mutation or mutations responsible in most cases are not identified.
Several genetic mutations have been found to cause autosomal dominantly inherited Parkinson disease. These are generally rare, although one gene, PARK8, has been described in up to 50% of patients with familial Parkinson disease of Middle Eastern or North African descent, and mutations in this gene are reported in almost 2% of patients with idiopathic, sporadic onset Parkinson disease.[9]
Three autosomal recessive forms are also known. Of these 3 forms, PARK2 (the parkin mutation), may be responsible for familial Parkinson disease in other inheritance patterns, and heterozygous mutations of this gene are reported in up to 10-20% of patients with onset earlier than age 40 years.
Dopamine-responsive dystonia is due to a 1 of 2 different mutations. The more common form, which occurs in an autosomal dominant inheritance pattern, is due to a mutation in a gene coding for the enzyme GTP-cyclohydrolase (GTPCH), which is involved in the synthesis of tetrahydrobiopterin, a cofactor needed for the enzyme tyrosine hydroxylase. A less common autosomal recessive form, due to a partial deficiency in tyrosine hydroxylase, also occurs.[10] As partial penetrance and new mutations have been described in patients with GTPCH-1 deficiency, a family history may not be present. In these disorders, dopamine is depleted in the striatum, but no cell degeneration occurs. Interestingly, one study reported that 3 of 10 families thought to have dopa-responsive dystonia actually had a mutation in the parkin gene instead, further illustrating the clinical overlap in these conditions.
The biochemical basis for cell degeneration is unknown. However, evidence exists that patients with Parkinson disease have a deficiency of the mitochondrial enzyme complex I in the midbrain. In cell culture and animal models, inhibitors of complex I enhance oxidant or excitatory amino acid toxicity to dopaminergic neurons.
In addition, mutations in of the genes implicated in Parkinson disease have been implicated in the formation of protein aggregation, protein misfolding, and defective proteosomal function. Oxidative stress and inflammation have also been implicated in the pathophysiology of Parkinson disease.[9]
Generally, no specific lab tests are needed in the evaluation of patients with Parkinson disease. In adolescents and young adults, Parkinson disease is extremely rare; therefore, other causes of parkinsonism need to be carefully excluded, particularly any exposure to antipsychotic or antiemetic medications. In very young patients or in patients with a family history of Parkinson disease, a genetic test for the parkin mutation may be considered and may be helpful to confirm the diagnosis.
Wilson disease should be considered carefully and workup should include screening of plasma ceruloplasmin; if low, measurement of 24-hour urinary copper excretion and slit-lamp examination for Kayser-Fleischer rings must be done.
Huntington disease can produce rigidity and bradykinesia in young adults or adolescents and may require DNA analysis for exclusion.
Neuroacanthocytosis can cause dystonia and rigidity in addition to other neurological features. The workup of this condition is discussed in more detail in Neuroacanthocytosis.
Dopa-responsive dystonia should be considered in patients with juvenile-onset dystonia and parkinsonism, particularly with diurnal fluctuations in symptoms. A number of tests are available.
The simplest test is a diagnostic trial of levodopa, as the response to low doses of levodopa is nearly complete.
Biochemical tests include measurement of cerebrospinal fluid concentrations of biopterin, neopterin, and the neurotransmitter metabolites homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 3 methoxy-4-hydroxyphenylglycol (MHPG). In both forms of dopa-responsive dystonia, an altered pattern of decreases in these compounds is observed.
Another biochemical test that is helpful in GTPCH-1 deficiency is to administer an oral dose of phenylalanine and then measure plasma amino acids at intervals.[11] In this condition, patients are less able to convert phenylalanine to tyrosine. The sensitivity and specificity of this test, though, is unknown.
A final method to test for this condition is by molecular genetic analysis; genetic tests are available for both GTPCH-1 deficiency and TH deficiency.[4]
Brain imaging is generally unnecessary in patients with typical Parkinson disease, especially if the patient has an asymmetric presentation, tremor, and a good response to medications.
Brain imaging (CT scan or MRI) must be obtained in patients younger than 50 years with atypical physical findings or an atypical history. Rare causes of parkinsonism that may be recognized on CT scan or MRI include basal ganglia calcification or iron deposition, hydrocephalus, multiple infarcts, multiple sclerosis, brain tumors, leukodystrophies, or striatal necrosis due to mitochondrial disease.
Single-photon emission CT (SPECT) and positron emission tomography (PET) are functional imaging studies that may show basal ganglia abnormalities in very mildly affected patients. These are not commercially available, however, and do not reliably differentiate Parkinson disease from other forms of parkinsonism.
Other imaging tests that use SPECT imaging and ligands that bind the dopamine transporter on presynaptic dopamine nerve terminals are under development and appear promising in the early detection of incipient Parkinson disease.
The approach to the medical treatment of Parkinson disease in younger patients is generally similar to that used in older individuals. However, younger patients seem to be at higher risk of developing complications with long-term levodopa treatment, particularly motor fluctuations, choreiform dyskinesias, and painful "off" dystonias. These motor complications are sometimes as disabling as tremor and bradykinesia and may persist despite multiple changes in medications.
Frequently, one or two target symptoms are the chief concern of younger patients, and control of these specific symptoms should be emphasized. Common problems include micrographia, pain (which can represent either dystonia or underlying bradykinesia), tremor, depression, fatigue, or anxiety. Each of these symptoms may be approached differently; for example, tremor may respond particularly well to anticholinergics, whereas fatigue may represent bradykinesia and may require levodopa or dopamine agonists.
Of the drugs that are commercially available, selegiline, rasagiline (monoamine oxidase B inhibitors), and dopamine agonists each have been studied for possible disease-altering effects. The early use of selegiline delays the need for levodopa by an average of 13 months in patients with very mild Parkinson disease, but the reasons for this effect are uncertain. Once patients are treated with levodopa, the rate of disease progression is not altered by selegiline, and therefore no convincing body of evidence exists to suggest that selegiline affects disease progression.
Rasagiline has also been studied for disease-altering effects in early Parkinson disease by comparing the change in Parkinson disease signs over time in patients treated with either 12 months of rasagiline or 6 months of placebo, followed by 6 months of rasagiline. In this delayed-start study, the subjects receiving rasagiline for the entire study had a slower decline than subjects whose treatment was delayed for 6 months. The magnitude of these changes was quite small, and further studies involving more patients for longer periods are needed.
The dopamine agonists pramipexole and ropinirole have also been studied in early Parkinson disease. In comparison to treatment with levodopa, patients treated with the dopamine agonists exhibited a reduced risk of the development of motor fluctuations and dyskinesias and showed greater retention of the uptake of radiolabeled tracer drugs in the basal ganglia over time. However, the uptake of these radiolabels is influenced by treatment with levodopa and dopamine agonists, and the significance of these changes in basal ganglia signal over time and the relationship to disease progression is unclear.
A number of studies have investigated the use of dopamine agonists as initial treatment. When administered as monotherapy, dopamine agonists have a very low risk of producing motor fluctuations or dyskinesias and may delay the need for administration of levodopa. This has been demonstrated recently in 2 large trials; in one trial, ropinirole was compared with levodopa under blinded conditions, and in the other, pramipexole was studied similarly. In both trials, these drugs were able to control symptoms of Parkinson disease in the majority of mildly affected patients.
After several years of treatment, the majority of patients may require a combination of both levodopa and a dopamine agonist. Whether the prevalence of motor fluctuations, dyskinesias, or psychiatric complications in patients treated with levodopa first and then given a dopamine agonist is any different after several years of combination treatment than patients who first receive a dopamine agonist has not been established. As the costs of dopamine agonists are considerably higher than the cost of levodopa, this question has significant implications.
Questions remain as to the effects of these drugs in altering the progression of the underlying pathology of Parkinson disease. Data exist to suggest that levodopa may be toxic in some animal models, but a recent clinical study of low- and high-dose levodopa in newly treated patients found no evidence of any acceleration of disease progression. In some animal models and cell culture experiments, some dopamine agonists appear to have a protective effect, but no clinical data are known to demonstrate this either, and the early use of dopamine agonists to delay disease progression cannot be recommended at the present time.
Treatment of other symptoms
In addition to treatment of the cardinal manifestations of Parkinson disease, a number of other symptoms, such as constipation, dysphagia, urinary retention or frequency, impotence, orthostatic hypotension, imbalance, and falls may require other treatment approaches.
Many patients have associated mood and sleep problems and may benefit from antidepressants, anxiolytics, and sedatives. In patients with more severe Parkinson disease, levodopa or dopamine agonists as well as other adjunctive medications may produce agitation, hallucinations, or psychosis. These symptoms should be managed by first discontinuing or reducing antiparkinsonian medications. Some patients improve with the use of donepezil or by using low doses of the atypical antipsychotics clozapine and quetiapine.
In young patients with motor fluctuations or dyskinesias that are refractory to medical treatments, stereotaxic neurosurgical treatments may be useful, particularly since younger patients usually do not have dementia or severe imbalance, which are contraindications to these treatments. These are discussed in detail in the article Surgical Treatment of Parkinson Disease.
Generally, patients with Parkinson disease are best treated and monitored by a neurologist, except in the early stage of the disease.
A urologist is consulted for evaluation and treatment of urinary frequency, urgency, incontinence, or erectile dysfunction.
A physiatrist, physical therapist, and occupational therapist may be able to improve the patient's ability to perform activities of daily living, reduce pain, and avoid fractures and compression neuropathies from falls. Botulinum injections for limb dystonia can be very helpful and are administered by specially trained physiatrists or neurologists.
A gastroenterologist and speech therapist may be needed to evaluate dysphagia, a common complication in patients with more advanced Parkinson disease. Excessive sialorrhea can be treated with botulinum toxin injections into the salivary glands, usually administered by otolaryngologists. In some patients, a gastrostomy may be needed to maintain adequate nutrition.
Psychiatric consultation may be required to control mood disorders and psychiatric symptoms, especially in patients with refractory depression or psychosis.
Neurosurgical consultation may be appropriate in patients with tremor, dyskinesias, motor fluctuations, or dystonia refractory to medical treatment.
Few dietary restrictions are needed in most patients with Parkinson disease who are not experiencing significant dysphagia.
Protein-restricted diets may be useful in patients who are experiencing motor fluctuations with long-term levodopa treatment. As levodopa is transported into the brain by a carrier protein that transports large neutral amino acids found in dietary protein, large protein meals can compete for the transport of levodopa and reduce or eliminate its effects. A protein-restricted diet can therefore improve the response to levodopa and can be useful in patients with otherwise refractory motor fluctuations.
Two general approaches are used for this diet. In one, the total daily protein requirement is spread more or less equally over the day. The other approach aims at consuming food very low in protein or not containing protein during the day and a high-protein meal in the evening.
Generally, these diets are difficult to follow; however, in patients with severe, unpredictable motor fluctuations, this approach may be worthwhile.
A number of different medications are used in the treatment of Parkinson disease. Drugs that improve motor symptoms include dopaminergic drugs—immediate and controlled-release levodopa; catechol-O -methyltransferase (COMT) inhibitors tolcapone and entacapone; and the dopamine agonists bromocriptine, ropinirole, and pramipexole. In addition, nondopaminergic drugs, including anticholinergics, selegiline, and amantadine can help motor symptoms as well.
Patients with Parkinson disease often benefit with treatment of psychological and behavioral symptoms. For depression, any of the standard antidepressants may be used. These include tricyclic antidepressants, such as amitriptyline, nortriptyline, and doxepin, as well as the selective serotonin reuptake inhibitors (SSRIs) paroxetine (Paxil), sertraline (Zoloft), fluoxetine (Prozac), and citalopram (Celexa). Newer antidepressants unrelated to SSRIs or tricyclic antidepressants include bupropion (Wellbutrin), venlafaxine (Effexor), nefazodone (Serzone), and mirtazapine (Remeron). Concern has been expressed about the risk of serotonin syndrome with the concomitant use of selegiline and the SSRIs; however, a survey of Parkinson disease specialists reported that these drugs often are combined with negligible evidence of toxicity.
Insomnia may be especially challenging to treat. Some patients having difficulty with sleep initiation may benefit from a benzodiazepine; however, because tachyphylaxis is very common with drugs in this class, a sedating antidepressant (eg, trazodone, amitriptyline) may be a better long-term choice. Other patients awaken with symptoms of Parkinson disease such as stiffness, dystonia, or tremor; in such patients, a nocturnal dose of levodopa or a dopamine agonist may be effective.
In addition to depression and insomnia, some patients experience psychiatric reactions with levodopa or dopamine agonists. These include visual hallucinations that can evolve into a delusional state in which auditory hallucinations, paranoia, psychosis, and violent behavior can occur. These problems are sometimes so severe that the use of a dopamine agonist is precluded; however, these reactions sometimes can be eliminated or treated effectively with an antipsychotic. Of the available antipsychotics, most agents worsen the symptoms of Parkinson disease and cannot be used; however, quetiapine and clozapine are well tolerated in most patients and may be very effective at low doses.
These agents are used for treatment of motor fluctuations in patients treated with levodopa for long periods. Tolcapone and entacapone are inhibitors of an enzyme, COMT, which converts levodopa into an inactive metabolite, 3-O -methyldopa. Coadministration delays clearance of levodopa from plasma and prolongs the action of individual doses of levodopa. Neither drug has any effect in Parkinson disease symptoms independent of levodopa.
Clinical Context:
Mechanism of action unknown, but possibly related to ability to inhibit COMT and alter plasma pharmacokinetics of levodopa. When given in conjunction with levodopa and an aromatic amino acid decarboxylase inhibitor, such as carbidopa, plasma levels of levodopa are more sustained than after administration of levodopa and an aromatic amino acid decarboxylase inhibitor alone. Sustained plasma levels of levodopa may result in more constant dopaminergic stimulation in brain, which may lead to greater effects on signs and symptoms of Parkinson disease as well as increased levodopa adverse effects, sometimes requiring decrease in dose of levodopa. Tolcapone enters CNS to minimal extent but has been shown to inhibit central COMT activity in animals. Should always be used as adjunct to levodopa/carbidopa therapy.
These agents comprise the dopaminergic agents, which stimulate dopaminergic receptors in basal ganglia; the MAO-B oxidase inhibitors, which prevent inactivation of dopamine by MAO-B and possibly the conversion of compounds into neurotoxic types; and the dopamine agonists (see separate Drug Category below).
Clinical Context:
Stalevo is a combination of levodopa, carbidopa, and entacapone. The medication is available in 6 strengths, containing 50, 75, 100, 125, 150, or 200 mg of levodopa. All sizes contain carbidopa at 25% of the milligram dose of levodopa and 200 mg of entacapone.
Clinical Context:
Available in US in combination with carbidopa, an inhibitor of dopa decarboxylase in GI mucosa. In Europe, levodopa sold in combination with benzaseride, another dopa decarboxylase inhibitor.
Used in patients with established Parkinson disease; most effective in relieving bradykinesia and rigidity; it is less consistently effective in relieving tremor and usually ineffective in relieving postural flexion, severe imbalance, freezing gait, dysarthria, and dysphagia.
In elderly patients, lower doses of levodopa should be used to initiate treatment. In patients on long-term levodopa therapy, higher doses usually are administered
Although no absolute dose limit, for patients to require more than 1.5 g/d is very unusual.
Clinical Context:
MAO-B oxidase inhibitor, FDA approved as adjunct to levodopa/carbidopa in patients who exhibit deterioration in response to that therapy. For patients who experience motor fluctuations on levodopa/carbidopa, addition of selegiline reduces "off" time, improves motor function, and allows levodopa dose reductions. If patient experiences increase in troublesome dyskinesia, reduce levodopa dose.
Irreversible inhibitor of MAO, acts as "suicide" substrate for enzyme such that MAO converts it to an active moiety that combines irreversibly with active site or enzyme's essential FAD cofactor. Blocks breakdown of dopamine and extends duration of action of each dose of L-dopa. Often allows L-dopa dose reduction that is needed for optimal effect.
Has greater affinity for type B than for type A active sites, thus serves as selective inhibitor of MAO type B at recommended dose. However, doses higher than 10 mg/d may significantly inhibit MAO-A sites. May inhibit dopamine reuptake. Metabolites, amphetamine and methamphetamine, may inhibit dopamine reuptake and enhance dopamine release.
Rapidly absorbed and has 73% bioavailability. Metabolized in liver to N-desmethylselegiline, L-amphetamine, and L-methamphetamine
Half-life approximately 10 h; metabolites excreted in urine.
Inhibition of MAO-B irreversible, thus loss of new protein synthesis activity, if it occurs, may last for several months.
After 2-3 d of treatment, attempt to reduce dose of levodopa/carbidopa. A 10-30% reduction is typical. Further reductions of levodopa/carbidopa may be possible during continued selegiline therapy.
Clinical Context:
Inhibits N -methyl-D-aspartic acid (NMDA) receptor-mediated stimulation of acetylcholine release in rat striatum. May enhance dopamine release, inhibit dopamine reuptake, stimulate postsynaptic dopamine receptors, or enhance dopamine receptor sensitivity.
Has efficacy as monotherapy and as adjunct to levodopa/carbidopa (or levodopa/benserazide in Europe) in treating Parkinson disease. Provides some benefit in tremor, rigidity, and bradykinesia.
Half-life is approximately 9-37 h and prolonged in renal insufficiency; 90% is excreted unchanged in urine
Clinical Context:
Irreversible MAO-B inhibitor that blocks dopamine degradation. Not metabolized to amphetamine derivatives. Main metabolite, aminoindan, has some activity and has been shown to improve motor and cognitive functions in experimental models. Indicated for Parkinson disease as initial monotherapy or as adjunctive therapy with levodopa.
These agents may be used either as monotherapy in patients not yet taking levodopa or as adjunctive therapy in patients taking levodopa who are experiencing motor fluctuations or dyskinesias.
In patients not yet taking levodopa, dopamine agonists may relieve signs and symptoms of Parkinson disease but are somewhat less effective than levodopa; use of this class of medications is most appropriate in patients with mild disease not affecting gait or balance.
This class of medications may allow introduction of levodopa to be delayed, thus reducing the risk of developing troublesome fluctuations and dyskinesias.
In patients already taking levodopa, dopamine agonists are useful as adjunctive therapy; these medications may prolong the duration of action of individual doses of levodopa, reduce the severity of motor fluctuations such as "off" bradykinesia and dystonia, allow the doses of levodopa to be lowered, and improve dyskinesias.
All drugs in this class should be initiated at low doses and the doses increased very slowly. The first few days are usually the most troublesome, but tolerance develops rapidly to many of the peripheral adverse effects such as nausea. Because of this, all of these drugs, except bromocriptine, are available at very small initial doses.
Clinical Context:Pergolide was withdrawn from the US market March 29, 2007, because of heart valve damage resulting in cardiac valve regurgitation. It is important not to abruptly stop pergolide. Health care professionals should assess patients' need for dopamine agonist (DA) therapy and consider alternative treatment. If continued treatment with a DA is needed, another DA should be substituted for pergolide. For more information, see FDA MedWatch Product Safety Alert and Medscape Alerts: Pergolide Withdrawn From US Market.
Dopamine agonist believed to exert therapeutic effect by directly stimulating postsynaptic dopamine receptors in nigrostriatal system. Usually administered in divided doses tid. During dosage titration, dosage of concurrent levodopa/carbidopa may be decreased cautiously.
Clinical Context:
Non-ergot dopamine agonist that has high relative in vitro specificity and full intrinsic activity at D2 subfamily of dopamine receptors, binding with higher affinity to D3- than to D2- or D4-receptor subtypes.
Has moderate affinity for opioid receptors. Metabolites have negligible affinity for dopamine D1, 5-HT1, 5-HT2, benzodiazepine, GABA, and muscarinic receptors and alpha1-, alpha2-, and beta-adrenoreceptors.
Precise mechanism of action in Parkinson disease unknown. However, possibly related to stimulation of dopamine receptors in striatum.
Discontinue gradually over 7-d period. Decrease frequency of administration from tid to bid for 4 d. For remaining 3 d, decrease frequency to once daily prior to complete withdrawal.
When administered as adjunct therapy to levodopa, concurrent dose of levodopa may be decreased gradually as tolerated.
Clinical Context:
Nonergot dopamine agonist with specificity of D2 dopamine receptor, but also has been shown to bind to D3 and D4 receptors and may stimulate dopamine activity on nerves of striatum and substantia nigra.
Clinical Context:
Elicits dopamine agonist effect. Indicated to treat acute immobility episodes (hypomobility or "off-periods") in Parkinson Disease. These episodes consist of inability to rise from a chair, speak, or walk and may occur toward the end of the dose interval or may be spontaneous and unpredictable in onset. Approximately 10 percent of individuals with stage IV Parkinson Disease who do not respond to standard medications for acute immobility may respond to apomorphine.
Clinical Context:
Semisynthetic, ergot alkaloid derivative; strong dopamine D2-receptor agonist; partial dopamine D1-receptor agonist; FDA approved as adjunct to levodopa/carbidopa, but less effective than other dopamine agonists.
Rarely used currently because of a concern of restrictive valvular heart disease, pleural, and retroperitoneal fibrosis common to all ergot derived drugs.
May relieve akinesia, rigidity, and tremor associated with Parkinson disease. Stimulates dopamine receptors in corpus striatum.
Approximately 28% absorbed from GI tract and metabolized in liver. Approximate elimination half-life is 50 h with 85% excreted in feces and 3-6% eliminated in urine. Initiate at low dosage; slowly increase dosage to individualize therapy. Maintain dosage during introductory period. Assess dosage titration every 2 wk. Gradually reduce dose in 2.5-mg decrements if severe adverse reactions occur.
Clinical Context:April 2008: A recall was issued for Neupro patch in the United States because of crystal formation in the patch resulting in decreased dopamine absorption transdermally. As of August 1, 2008, the patch is still unavailable, although the manufacturer is working to correct the defect and hopefully return it to the market. For more information see Medscape News.
Dopamine agonist stimulating D3, D2, and D1 receptors. Improvement in Parkinson-related symptoms thought to be its ability to stimulate D2 receptors within the caudate putamen in the brain. Available as transdermal patch that provides continuous delivery for 24 h (2 mg/24 h [10 cm2], 4 mg/24 h [20 cm2], or 6 mg/24 h [30 cm2]). Indicated for symptoms of early Parkinson disease.
These agents are used in the treatment of tremor and dystonia (painful or painless involuntary muscular contractions); they are most useful in patients with tremor. They can be administered as monotherapy or in combination with other drugs and usually are administered tid/qid; they may be effective in relieving dystonia in patients with motor fluctuations. Parenteral benztropine and diphenhydramine produce sedation, therefore, patients should not drive after receiving these medications.
Clinical Context:
Has strong anticholinergic and sedative properties. In patient with severe tremor, IV diphenhydramine can be used as adjunct for minor surgery or to facilitate detailed examination.
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