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Basics ⬇

Boyd Koffman, MD, PhD

BASICS

DESCRIPTION navigator

Toxic myopathies are potentially reversible muscle disorders due to myotoxicity of prescribed or illicit drugs. Suspicion of a toxic myopathy is increased when there is temporal association of drug use prior to symptom onset, absence of preexisting neuromuscular symptoms, and improvement of symptoms after withdrawal of suspected toxin. Tentative classification based on the pathogenetic mechanism has been proposed, although knowledge of the mechanism of many toxins is limited. Several authors classify according to whether the myopathy is painful, painless, presence of an associated neuropathy, histopathologic features, drugs of abuse, and focal myopathies.

EPIDEMIOLOGY navigator

RISK FACTORS navigator

Genetics navigator

GENERAL PREVENTION navigator

ALERT navigator

The incidence of rhabdomyolysis is increased when statins are combined with other drugs, especially simvastatin and:

Anticipating drug–drug interactions may help prevent statin-induced myotoxicity

ALERT navigator

FDA notified healthcare professionals that it recommends limiting the use of the highest approved dose of the cholesterol-lowering medication simvastatin (80 mg) because of increased risk of muscle damage. RECOMMENDATION: Simvastatin 80 mg should not be started in new patients, including patients already taking lower doses of the drug.

PATHOPHYSIOLOGY navigator

The mechanism varies depending on the agent. Syndromes include:

ETIOLOGY navigator

COMMONLY ASSOCIATED CONDITIONS navigator

[Outline]

Diagnosis ⬆ ⬇

DIAGNOSIS

HISTORY navigator

Myopathic weakness begins after a suitable duration of exposure to a presumed toxin. There is usually no preexisting neuromuscular condition, and symptoms of weakness resolve following removal of the offending agent.

PHYSICAL EXAM navigator

DIAGNOSTIC TESTS AND INTERPRETATION

Lab

Initial Lab Tests navigator

Laboratory procedures to consider when a toxic myopathy is suspected should be based on suspicions elicited from the history.

Diagnostic Procedures/Other navigator

Pathological Findings navigator

Types of injuries incurred by myofibers or their organelles and identified on muscle biopsy:

DIFFERENTIAL DIAGNOSIS navigator

There should be no other identifiable cause of myopathy present. Differential diagnoses are listed by clinical and pathologic findings and may be listed more than once if more than one mechanism of presentation has been described.

Painful Toxic Myopathies navigator

Painless Toxic Myopathies navigator

[Outline]

Treatment ⬆ ⬇

TREATMENT

ADDITIONAL TREATMENT

General Measures navigator

Most cases of toxic myopathy require removal of the potentially offending agent.

Issues for Referral navigator

The U.S. Food and Drug Administration (FDA) encourages voluntary reporting of adverse events, defined as “any undesirable experience associated with the use of a medical product in a patient.” A report should be made when use of a medication causes disability or death, requires medical intervention or hospitalization, or may jeopardize a patient.

Reports (see the Internet site http://www.fda.gov/Safety/MedWatch/HowToReport/ucm085568.htm) may be submitted via postage-paid MedWatch form; by phone: 1-800-FDA-1088; by Fax: 1-800-FDA-0178; or via Internet (Medwatch online) at https://www.accessdata.fda.gov/scripts/medwatch/medwatch-online.htm

Additional Therapies navigator

SURGERY/OTHER PROCEDURES navigator

IN-PATIENT CONSIDERATIONS

Initial Stabilization navigator

Admission Criteria navigator

IV Fluids navigator

Hydration for hyperthermia and to prevent renal failure in rhabdomyolysis or myoglobinuria

Nursing navigator

Discharge Criteria navigator

[Outline]

Ongoing Care ⬆ ⬇

ONGOING-CARE

FOLLOW-UP RECOMMENDATIONS

Patient Monitoring navigator

PATIENT EDUCATION navigator

PROGNOSIS navigator

COMPLICATIONS navigator

[Outline]

Additional Reading ⬆ ⬇

SEE-ALSO

Codes ⬆ ⬇

CODES

ICD9

Clinical Pearls ⬆