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CARDIOVASCULAR

Myopathies

Article Last Updated: Nov 21, 2007

AUTHOR AND EDITOR INFORMATIONSection 1 of 9 Authors and Editors Introduction

Clinical Differentials Workup Treatment Medication Follow-up References

Author: A Bethel, MD, MPH, Clinical Assistant Professor, Department of

Emergency Medicine, Mercy Catholic Medical Center, Drexel University School of

Medicine

A Bethel is a member of the following medical societies: American

Academy of Emergency Medicine and American College of Emergency Physicians

Editors: Jerry Balentine, DO, Professor of Emergency Medicine, New York College

of Osteopathic Medicine; Senior Vice President, Chief Medical Officer, Medical

Director, Attending Physician in Department of Emergency Medicine, Saint

Barnabas Hospital; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor,

eMedicine; Blackburn, DO, FACOEP, FACEP, Program Director, Department of

Emergency Medicine, Maricopa Medical Center; Assistant Professor, Department of

Surgery, University of Arizona; 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; 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 and Editor Disclosure

Synonyms and related keywords: disorder of skeletal muscle, myonosus,

sarcoidosis, polymyositis, dermatomyositis, idiopathic myopathies, connective

tissue disease, systemic lupus erythematosus, SLE, rheumatoid arthritis, RA,

polyarteritis nodosa, acute alcoholic myopathy, drug-induced myopathy,

thyrotoxic periodic paralysis, Conn syndrome, primary hyperaldosteronism,

muscular dystrophy

INTRODUCTIONSection 2 of 9 Authors and Editors Introduction Clinical

Differentials Workup Treatment Medication Follow-up References

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 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, 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.

CLINICALSection 3 of 9 Authors and Editors Introduction Clinical

Differentials Workup Treatment Medication Follow-up References

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,

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.

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)

sackie 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 and other statins

Cocaine

Colchicine

Amiodarone and others that inhibit CYP3A4 when combined with simvastatin

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.

DIFFERENTIALSSection 4 of 9 Authors and Editors Introduction Clinical

Differentials Workup Treatment Medication Follow-up References

Guillain-Barré Syndrome

Lambert-Eaton Myasthenic Syndrome

Myasthenia Gravis

Tick-Borne Diseases, Introduction

WORKUPSection 5 of 9 Authors and Editors Introduction Clinical Differentials

Workup Treatment Medication Follow-up References

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

AST

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

TREATMENTSection 6 of 9 Authors and Editors Introduction Clinical

Differentials Workup Treatment Medication Follow-up References

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

MEDICATIONSection 7 of 9 Authors and Editors Introduction Clinical

Differentials Workup Treatment Medication Follow-up References

Management is supportive.

FOLLOW-UPSection 8 of 9 Authors and Editors Introduction Clinical

Differentials Workup Treatment Medication Follow-up References

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

REFERENCESSection 9 of 9 Authors and Editors Introduction Clinical

Differentials Workup Treatment Medication Follow-up References

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Griggs RC, Ptacek LJ. The periodic paralyses. Hosp Pract (Off Ed). Nov 15

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Plate AM, Boyle BA. Musculoskeletal manifestations of HIV infection. AIDS Read.

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Riggs JE, Schochet SS, Joynt RJ, Griggs RC, eds. Muscle disease. In: Clinical

Neurology. Vol 4. 1997:1-37.

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etiologies, pathophysiology, presentation, and therapy. Am J Emerg Med. Mar

1992;10(2):143-8. [Medline].

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Tintinelli JE, Krome RL, Ruiz E. Emergency Medicine: A Comprehensive Study

Guide. 4th ed. McGraw-Hill; 1996:1036.

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2002;14(6):643-7. [Medline].

Myopathies excerpt

Article Last Updated: Nov 21, 2007