Toxic and Drug Induced Myopathies

One of the best and most concise review articles that I could find on the subject is Toxic and Drug Induced Myopathies. It was published in the Journal of Neurology, Neurosurgery & Psychiatry in 2009. It is available for a fee here.

Another version of the article is posted free here, however it is not 100% identical in terms of content to the one that you have to pay for. For example, there is a cool histopathology slide in the for-fee article that’s not in the free version.

Anyway, I will sum up some key concepts about toxic myopathies.

The main causes of toxic myopathy are:

• Statins and other antihyperlipidemic agents such as gemfibrozil
• Glucocorticoids and other immunosuppressors such as alpha-interferon and colchicine
• Ethanol
• Cocaine and other stimulants such as PCP and amphetamine
• Antipsychotics, notably in the context of neuroleptic malignant syndrome
• Antiretroviral agents such as zidovudine and fialuridine
• Antimalarials such as chloroquine and hydroxychloroquine.

The presentation can be muscle pain, weakness, muscle tenderness, creatine kinase elevation, acute renal failure, fever, or some combination of all of these.

Treatment is to stop or taper the offending agent, along with supportive measures, such is IV hydration or physical therapy, as needed.

There are a few of situations where the diagnosis gets a bit more difficult (read: here comes some good internal medicine Board question material). For example, you might be expected to know how to diagnose glucocorticoid-induced myopathy in a patient who is on glucocorticoids for an inflammatory myopathy. A typical picture would be worsening myopathy in the face of improving creatine kinase that begins several weeks after starting high doses of systemic glucocorticoid treatment.

Another Board-fodder-type question revolves around distinguishing critical illness myopathy from critical illness polyneuropathy. One distinguishing feature is that in a pure critical illness myopathy, sensation should be normal. UpToDate treats this topic very well under the heading Neuromuscular weakness related to critical illness.