AUTHOR INFORMATION

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

Courtney A Bethel, MD, MPH, is a member of the following medical societies: American Academy of Emergency Medicine, and American College of Emergency Physicians

Edited by Jerry Balentine, DO, Professor of Emergency Medicine, New York College of Osteopathic Medicine; Medical Director, Saint Barnabas Hospital; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Paul Blackburn, DO, Program Director, Department of Emergency Medicine, Maricopa Medical Center; Assistant Professor, Department of Surgery, University of Arizona; John Halamka, MD, Chief Information Officer, CareGroup Healthcare System, Assistant Professor of Medicine, Department of Emergency Medicine, Beth Israel Deaconess Medical Center; Assistant Professor of Medicine, Harvard Medical School; and Charles V Pollack, Jr, MD, MA, FACEP, Professor, Department of Emergency Medicine, University of Pennsylvania College of Medicine; Chairman, Department of Emergency Medicine, Pennsylvania Hospital

Author's Email:	Courtney A Bethel, MD, MPH
Editor's Email:	Jerry Balentine, DO

eMedicine Journal, June 21 2005, VOLUME 6, Number 6

INTRODUCTION

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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 with attention to airway and aspiration precautions and providing supportive care are indicated while inpatient consultation and detailed studies are performed.

Pathophysiology: Most congenital 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, 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.

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.

Mortality/Morbidity:

• 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.

CLINICAL

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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, azidothymidine (AZT), alcohol, colchicine, pentachlorophenol (PCP), heroin, and a myriad of other medications may cause myopathies.

• Occupational and travel history may lead a physician to consider ingestion of barium chloride or carbonate as a cause for acute hypokalemic paralysis.
  • These are absorbable salts (in contrast to nonabsorbable, safe, widely used barium sulfate) that may contaminate table salt or flour. Absorbable salts may be used industrially for glazing pottery.

  • Paralysis results when passive efflux of potassium is blocked at the cell membrane and elevated intracellular potassium decreases the resting membrane potential.

• Symptoms noted generally include the following:

• Symmetric proximal muscle weakness

• Malaise

• Fatigue

• Patient may note dark colored urine and/or fever.

• No sensory complaints or paresthesias are noted with myopathies.

• Atrophy and hyporeflexia are very late findings in most patients with myopathy. The early presence of these findings usually implicates neuropathies.

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

• Acuity of symptom onset aids in diagnosis.

• Weakness progressing over hours suggests a toxic etiology or one of episodic paralyses.

• Weakness developing over days suggests acute dermatomyositis or rhabdomyolysis.

• Symptom development over a period of weeks suggests polymyositis, steroid myopathy, or myopathy resulting from endocrine causes (eg, hyperthyroidism, hypothyroidism).

• Symptoms of the patient indicate which muscle groups are involved.

• Difficulty rising from chairs, getting out of the bathtub, climbing stairs, and/or shaving or combing the hair suggests proximal muscle weakness.

• Weakness of distal muscles will present with symptoms of weak grasp, handwriting problems, and walking difficulties, (eg, flapping gait).

Physical:

• Objective weakness, usually in a symmetric distribution of proximal muscle groups is observed.

• Muscle tenderness is rare.

• Fever, particularly with pyomyositis or polymyositis may occur.

• Muscle mass should be normal. Atrophy is a very late sign with muscle disorders.

• Normal level of consciousness should be preserved.

• Deep tendon reflexes (DTRs) and sensory perception should be normal. DTRs may be diminished or absent in hypokalemic paralysis.

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

Causes:

• 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.

• Significance of acute alcoholic myopathy is that the precipitation of myoglobin in the renal tubules can cause acute renal tubular necrosis.

• Aggressive hydration and, occasionally, administration of mannitol and furosemide to increase diuresis, are essential to maintain renal function.

• Alcohol, in addition to the acute syndrome of muscle necrosis, causes a more chronic myopathy associated with gradual progressive weakness and atrophy that usually involves the hip and shoulder girdle. This chronic myopathy does not result in myoglobinuria or elevated creatine kinase-MM (CK-MM) levels.

• Infectious causes include the following:

• Trichinosis

• Cysticercosis (Taenia solium)

• Toxoplasmosis

• Human immunodeficiency virus (HIV)

• Coxsackie A and B viruses

• Influenza

• Lyme disease

• Staphylococcus aureus muscle infection (frequent cause of pyomyositis)

• Endocrine causes of myopathy include the following:
  • Addison disease, particularly when fluid and electrolyte problems are present

  • Cushing disease

  • Hypothyroidism (CK may be mildly elevated)

  • Hyperthyroidism (CK may be normal)

  • Hyperparathyroidism

• Drug-induced or toxic causes of myopathy include use of the following:
  • Steroids (especially with prolonged high doses, divided doses over 25 mg/d, fluorinated steroid use)

  • AZT

  • Lovastatin

  • Cocaine

  • Colchicine

• Acute periodic paralysis may be classified as hypokalemic, hyperkalemic, or normokalemic.
  • Normokalemic paralysis causes the most severe and prolonged attacks.

  • Patients usually feel well between attacks, but some have myotonia (ie, muscle stiffness) or residual weakness after repeated episodes.

  • A genetic defect has been linked to these diseases, but in some instances, hypokalemia may cause acute weakness in healthy individuals.

• Acute hypokalemic periodic paralysis may be primary (ie, familial) or secondary to excessive renal or GI losses or endocrinopathy. In these cases, intracellular shift of potassium depolarizes the cell membrane rendering it inexcitable and no muscle contraction can occur; hence, the patient experiences paralysis. This may occur independent of the sodium-potassium pump.

• Familial periodic paralysis usually occurs in Caucasian males, is autosomal dominant, and may last as long as 36 hours.

• Attacks usually occur at night or in early morning upon awakening and can be precipitated by a diet high in carbohydrates, rest following exercise, or glucose and insulin given intravenously.

• 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.

• Duchenne dystrophy, observed in boys younger than 5 years, causes the most severe disease. Cardiomyopathy is common in affected children.

• Weakness and muscle wasting in a child with elevated CK occurs with Duchenne dystrophy, but other dystrophies (eg, fascioscapulohumeral, limb-girdle, myotonic) may occur in boys and girls with normal muscle enzyme levels.

• Patients with mild cases may lead fairly normal lives, but progressive weakness and scoliosis impairing pulmonary function often results in recurrent infections and exacerbation of weakness.

DIFFERENTIALS

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Guillain-Barré Syndrome
Lambert-Eaton Myasthenic Syndrome
Myasthenia Gravis
Tick-Borne Diseases, Introduction

WORKUP

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Lab Studies:

• CK with isoenzymes

• Electrolytes, calcium, magnesium

• Serum myoglobin

• Serum creatinine and BUN

• Urinalysis: Myoglobinuria is indicated by positive urinalysis with few RBCs on microscopic evaluation.

• Complete blood count

• Erythrocyte sedimentation rate

• Thyroid function tests

Other Tests:

• Electrocardiogram - Findings suggesting hypokalemia include the following:

• Diffuse nonspecific ST-T wave changes

• Increased PR interval

• U waves

• Wide QRS

• 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:

• Genetic testing

• Antinuclear antibody (ANA)

• MRI

• Electromyogram (EMG)

• Muscle biopsy

TREATMENT

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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.

• Swallowing usually is not impaired, and oral supplementation may blunt the acute attack.

• IV potassium should be given cautiously, if used at all.

• Attacks will resolve spontaneously within 4-24 hours, and hyperkalemia may result if potassium supplementation has been excessive.

• Spironolactone and acetazolamide are useful for prophylaxis of attacks.

• In patients with hyperkalemic periodic paralysis, attacks are often so brief that no therapy is needed.

• Some patients find that carbohydrate loading at the onset of symptoms may lessen the attack.

• Glucose and insulin may be useful in lowering serum potassium levels. Kayexalate has not been shown to be effective.

Consultations:

• Neurologist

• Rheumatologist

• Infectious disease specialist

MEDICATION

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Management is supportive.

FOLLOW-UP

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Complications:

• Cardiac arrhythmias

• Hypertension

• Dysphagia

• Acute gastric dilation

• Respiratory failure

• Endocrinopathies

• Cataracts

• Sensorineural hearing loss

• Seizures and cerebral dysplasias

• Early death

Prognosis:

• Varies depending on the etiology

TEST QUESTIONS

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CME Question 1: A 29-year-old man presents to the ED after partying on the 4th of July weekend. He complains of weakness, leg pain, and blood in the urine. His urinalysis reveals 4+ blood, 0-3 RBC, and 0-3 WBC count. What is the most likely cause of these symptoms?

A: Kidney stone
B: Prostate cancer
C: Rhabdomyolysis
D: Urinary tract infection
E: Coagulopathy

The correct answer is C: Rhabdomyolysis also is known as acute alcoholic myopathy. Treatment includes adequate hydration to prevent myoglobin precipitation in renal tubules, which may cause renal failure.

CME Question 2: A 48-year-old, severely asthmatic woman presents to the ED complaining of diffuse body aches and weakness that have been occurring for 1 month. She denies fever or chills but says her asthma tends to flare this time of year; therefore, she has been taking extra medication. What medication is most likely the culprit?

A: Albuterol inhaler
B: Ipratropium bromide inhaler
C: Theophylline
D: Dexamethasone
E: Triamcinolone acetate inhaler

The correct answer is D: Dexamethasone in prolonged or high doses may cause steroid myopathy. For patients taking theophylline, also consider hypokalemia due to diuretic effect.

Pearl Question 1 (T/F): Painless, slow, progressive difficulty climbing stairs, rising from chairs, or getting into or out of a bathtub without any complaints of numbness suggest myopathy involving proximal muscles.

The correct answer is True: Myopathy is a muscle disease unrelated to any disorder of innervation or neuromuscular junction. Etiologies vary widely, with the common symptoms of muscle weakness, impaired function in activities of daily life, and, rarely, muscle pain and tenderness. Symptoms of the patient indicate which muscle groups are involved. Difficulty rising from chairs, getting out of the bathtub, climbing stairs suggests proximal leg muscle weakness.

Pearl Question 2 (T/F): A high carbohydrate diet, rest after exercise, thyrotoxicosis, and barium carbonate or barium chloride poisoning may all cause acute hypokalemic paralysis in susceptible patients.

The correct answer is True: Attacks of hypokalemic paralysis can be precipitated by a diet high in carbohydrates, rest following exercise, and glucose and insulin given intravenously. Thyrotoxic periodic paralysis and Conn syndrome (ie, primary hyperaldosteronism) occur in Asians and are considered to have low potassium as the mechanism for paralysis. Occupational and travel history may lead a physician to consider ingestion of barium chloride or carbonate as a cause for acute hypokalemic paralysis.

Pearl Question 3 (T/F): Steroids used to treat myopathy may also cause a myopathic disorder.

The correct answer is True: Steroids may be used to treat polymyositis, but they may cause a myopathy. A brief trial of steroid withdrawal may help to distinguish between the 2 causes of exacerbated weakness in these patients. Azidothymidine (AZT) is a treatment for HIV disease, which has been shown to cause myopathy.

Pearl Question 4 (T/F): Infection should be considered a possible cause of myopathy.

The correct answer is True: Trichinosis, toxoplasmosis, HIV, cysticercosis, and Lyme disease are some of the infectious causes of myopathy.

BIBLIOGRAPHY

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• Bennett JC, Plum F: Myopathies. In: Cecil Textbook of Medicine. 20th ed. WB Saunders Co; 1996:1500-03, 2158-73.
• Fauci AS, Braunwald E, Isselbacher KJ, Wilson JD: In: Harrison's Principles of Internal Medicine. 14th ed. McGraw-Hill; 1998:2473-2483.
• Griggs RC, Ptacek LJ: The periodic paralyses. Hosp Pract (Off Ed) 1992 Nov 15; 27(11): 123-6, 129-30, 136-7[Medline].
• Plate AM, Boyle BA: Musculoskeletal manifestations of HIV infection. AIDS Read 2003 Feb; 13(2): 62, 69-70, 72, 76[Medline].
• Riggs JE, Schochet SS, Joynt RJ, Griggs RC, eds: Muscle disease. In: Clinical Neurology. Vol 4. 1997:1-37.
• Stedwell RE, Allen KM, Binder LS: Hypokalemic paralyses: a review of the etiologies, pathophysiology, presentation, and therapy. Am J Emerg Med 1992 Mar; 10(2): 143-8[Medline].
• Stobo JD, Hellman DB: Myopathies. In: The Principles and Practice of Medicine. 23rd ed. McGraw-Hill; 1996:898-904.
• Tintinelli JE, Krome RL, Ruiz E: In: Emergency Medicine: A Comprehensive Study Guide . 4th ed. McGraw-Hill; 1996:1036.
• Wortmann RL: Lipid-lowering agents and myopathy. Curr Opin Rheumatol 2002 Nov; 14(6): 643-7[Medline].

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