Myopathies

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Practice Essentials

A myopathy is a muscle disease unrelated to any disorder of innervation or neuromuscular junction. These conditions have widely varying etiologies, including congenital or inherited, idiopathic, infectious, metabolic, inflammatory, endocrine, and drug-induced or toxic.

History

Important information to obtain during the patient’s history includes the following:

Signs and symptoms

The common symptoms of myopathy are muscle weakness, impaired function in activities of daily life, and, rarely, muscle pain and tenderness. Significant muscle pain and tenderness without weakness should prompt consideration of other causes.

General signs and symptoms of myopathy include the following:

The acuity of symptom onset may aid in the diagnosis, as follows:

Indications of which muscle groups are involved include the following symptoms:

See Clinical Presentation for more detail.

Diagnosis

Laboratory testing

The following laboratory tests may be used to evaluate patients with myopathies:

Other studies may include the following:

See Workup for more detail.

Management

The treatment of a myopathy is dependent on its etiology and can range from supportive and symptomatic management to therapy for specific conditions. Such treatments may include the following:

See Treatment for more detail.

Background

Myopathy is a muscle disease unrelated to any disorder of innervation or neuromuscular junction. Etiologies vary widely. The common symptoms are muscle weakness, impaired function in activities of daily life, and, rarely, muscle pain and tenderness. Presence of discolored or dark urine suggests myoglobinuria.

For the emergency physician, it is important to distinguish neurologic from muscular dysfunction. However, in the face of profound weakness, establishing ABCs (airway, breathing, circulation) with attention to airway and aspiration precautions and providing supportive care are indicated while inpatient consultation and detailed studies are performed.

Pathophysiology

Most congenital myopathies or inherited myopathies are chronic slowly progressive diseases. The emergency physician rarely attends to a patient specifically to treat congenital myopathy unless acute deterioration occurs. Emergency physicians attend to patients with metabolic,[1] inflammatory, endocrine, and toxic causes of myopathy more often than those with congenital causes because of the acute or subacute onset of symptoms associated with noncongenital forms.[2]

Periodic paralyses are a group of diseases that cause patients to present with acute weakness due to potassium shifts, leading to muscle dysfunction. A genetic defect of the sodium ion channel in muscle cell membranes is responsible for the paralysis, which may last from hours to days.

Etiology

Idiopathic myopathies are thought to result from immune-mediated phenomena including sarcoidosis with myopathy, polymyositis, and dermatomyositis. Some idiopathic myopathies are associated with connective tissue disease, eg, systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and polyarteritis nodosa.

Acute alcoholic myopathy should be considered in patients who, after binging on alcohol, present with muscle pain that mostly involves limb weakness and myoglobinuria. Note the following:

Infectious causes include the following:

Endocrine causes of myopathy include the following:

Drug-induced or toxic causes of myopathy include use of the following[4] :

Acute periodic paralysis may be classified as hypokalemic, hyperkalemic, or normokalemic. Note the following:

Thyrotoxic periodic paralysis and Conn syndrome (ie, primary hyperaldosteronism) occur in Asians and are considered to have low potassium as the mechanism for paralysis. Treatment of the underlying disease and electrolyte disorder are curative.

Excessive licorice ingestion, as well as a myriad of other causes of hypokalemia, can cause paralysis.

Muscular dystrophies are chronic, progressive, inherited myopathies that present from early childhood to adolescence, as follows:

Prognosis

The prognosis varies depending on the etiology. The morbidity and mortality of myopathies is related to the etiology of the condition, severity of disease, and the presence of comorbid conditions. Severe weakness may lead to respiratory failure and death.

Thyrotoxic hypokalemic periodic paralysis is known to occur in Asian men, and one study suggests that Polynesians are also at risk for this condition.[7]

History

Obtain the family history to determine presence of periodic paralysis or muscular dystrophy. Personal history of autoimmune disease, endocrinopathy, renal insufficiency, and/or alcoholism should be noted.

Discuss any previous episodes of severe weakness, particularly any that occurred after exercise or exposure to cold temperatures, which may indicate one of the periodic paralyses. Some patients with familial hypokalemic periodic paralysis may note that the symptoms occur after eating high-carbohydrate meals.

History of medication use is very important. Steroids, lipid-lowering agents,[8] retroviral agents, alcohol, colchicine, pentachlorophenol (PCP), heroin, and a myriad of other medications may cause myopathies. In some cases, the combination of multiple myopathic agents is responsible for the acute deterioration.[9]

Occupational and travel history may lead a physician to consider ingestion of barium chloride or carbonate as a cause for acute hypokalemic paralysis. Note the following:

Symptoms noted generally include the following:

Significant muscle pain and tenderness without weakness should prompt physicians to consider other causes.

Acuity of symptom onset aids in diagnosis, as follows:

Symptoms of the patient indicate which muscle groups are involved, as follows:

Physical Examination

Objective weakness, usually in a symmetric distribution of proximal muscle groups is observed. Muscle tenderness is rare; muscle mass should be normal. Atrophy is a very late sign with muscle disorders. Deep tendon reflexes (DTRs) and sensory perception should be normal. DTRs may be diminished or absent in hypokalemic paralysis.

Fever may occur, particularly with pyomyositis or polymyositis. Normal level of consciousness should be preserved.

Skin examination may reveal Gottron papules, which are pink-to-violaceous scaly areas over knuckles, elbows, and knees in dermatomyositis.

Complications

Complications of myopathy include the following:

 

Laboratory Studies

The following laboratory tests may be used to evaluate patients with myopathies:

Other Tests

Electrocardiography

Electrocardiographic (ECG) findings suggestive of hypokalemia include the following:

Other studies

Steroid therapy should be withheld until a definitive diagnosis is made, but many tests that are essential for distinguishing among the varied causes of myopathy are out of the scope of the emergency physician. These tests include the following:

Emergency Department Care

Respiratory insufficiency, associated cardiomyopathy, heart block, and aspiration may result from severe myopathy. Management is supportive.

Patients with rhabdomyolysis warrant inpatient and critical care admission to manage potentially life-threatening renal complications and hyperkalemia.

In patients with hypokalemic periodic paralysis, IV or oral potassium replacement may be indicated. Note the following:

In patients with hyperkalemic periodic paralysis, attacks are often so brief that no therapy is needed. Note the following:

Consultations

Consultation with one or more of the following services may be useful:

What are myopathies?What should be the focus of history in the evaluation of myopathies?What are the signs and symptoms of myopathies?How does the acuity of symptom onset aid in the diagnosis of myopathies?Which symptoms aid in determining which muscle groups are involved with myopathies?Which tests are performed in the evaluation of myopathies?What are the treatment options for myopathies?What are myopathies?What is the pathophysiology of myopathies?What is etiology of idiopathic myopathies?What is acute alcoholic myopathies?What are the infectious causes of myopathies?What are the endocrine causes of myopathies?Which medications may cause myopathy?What is acute periodic paralysis?What are thyrotoxic paralysis and Conn syndrome?What are muscular dystrophies?What is the prognosis of myopathies?What should be the focus of history in the evaluation of suspected myopathies?What are the symptoms of myopathies?What is the significance of acuity of symptom onset in the evaluation of myopathies?Which symptoms help to determine which muscle group is involved in a suspected myopathy?Which physical findings suggest myopathies?What are the complications of myopathies?What are the differential diagnoses for Myopathies?Which lab tests are performed in the evaluation of myopathies?Which electrocardiographic (ECG) findings suggest hypokalemia in patients with myopathies?Which tests may be performed to identify the cause of myopathy?What is included in emergency department care (ED) of myopathies?Which specialist consultations may be beneficial in the treatment of myopathies?

Author

Courtney A Bethel, MD, MPH, Clinical Assistant Professor, Department of Emergency Medicine, Mercy Catholic Medical Center, Drexel University School of Medicine

Disclosure: Nothing to disclose.

Specialty Editors

Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Paul Blackburn, DO, FACOEP, FACEP, Attending Physician, Department of Emergency Medicine, Maricopa Medical Center

Disclosure: Nothing to disclose.

Chief Editor

Barry E Brenner, MD, PhD, FACEP, Professor of Emergency Medicine, Professor of Internal Medicine, Program Director for Emergency Medicine, Sanz Laniado Medical Center, Netanya, Israel

Disclosure: Nothing to disclose.

Additional Contributors

Jerry R Balentine, DO, FACEP, FACOEP, Vice President, Medical Affairs and Global Health, New York Institute of Technology; Professor of Emergency Medicine, New York Institute of Technology College of Osteopathic Medicine

Disclosure: Nothing to disclose.

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