Health Questions and Answers

Myopathies

Which tests and procedures are used in the diagnostic evaluation of a patient with a suspected myopathy?
The diagnostic evaluation of a myopathy generally entails a triad of tests:

  • Serum creatine kinase (CK)
  • Electromyography (EMG)
  • Muscle biopsy

Explain the significance of serum CK.
Muscle destruction usually liberates CK, making elevation of this enzyme a good screening test for muscle disease. (The MM isoenzyme of CK is the most common.)

What can you learn from the EMG?
An EMG is done by inserting a fine-needle electrode into the muscle to record the electrical impulses related to contractions. Myopathies cause low-voltage, short-duration muscle contractions, and this test can thus confirm the presence of myopathy.

Summarize the role of muscle biopsy.
A muscle biopsy is often needed to define the cause of a myopathy, since most myopathies are clinically similar. The tissue may show inflammation (polymyositis), mitochondrial abnormalities, or other specific diseases.

List the most important myopathies.

  • Muscular dystrophies (e.g., Duchenne’s muscular dystrophy)
  • Congenital myopathies (e.g., Kearns-Sayre syndrome, central cord syndrome)
  • Inflammatory myopathies (e.g., polymyositis, dermatomyositis)
  • Toxic myopathies (e.g., alcohol, zidovudine, clofibrate, steroids)
  • Endocrine myopathies (e.g., hypothyroidism, hypoadrenalism)
  • Infectious myopathies (e.g., trichinosis, AIDS)

Which of the myopathies is most common on the medical ward?
Polymyositis is the most common. It is an inflammatory, T cell-mediated autoimmune disease of the muscles, characterized by the subacute onset of proximal weakness of the arms and legs, often with dysphagia. It may accompany connective tissue disease (such as systemic lupus erythematosus) or vasculitis but usually appears alone. It runs a variable course but can be severe or even fatal.

Which is the second most common myopathy?
Dermatomyositis is a distinct clinical entity characterized by similar subacute proximal muscle weakness in association with a rash, often over the face and trunk. Dermatomyositis is a humeral-mediated microangiopathy. It has an increased incidence of concomitant malignancies.

How are polymyositis and dermatomyositis treated?
Treatment for polymyositis and dermatomyositis is the same and involves high-dose oral prednisone (at least 1 mg/kg body weight/day) as the mainstay of therapy. Azathioprine or methotrexate may be used in steroid-resistant cases or when complications develop from steroid use. IV immunoglobulin (IVIG) may also be safe and effective, especially during acute exacerbations.

References
WEB SITES
www.neuroguide.com
www.aan.com (American Academy of Neurology)
www.medmatrix.org
www.internets.com/mednets/sneurolo.htm
www.medwebplus.com/subject/Neurology.html

BIBLIOGRAPHY

  • Briember HR, Amato AA: Dermatomyositis and polymyositis. Curr Treat Opt Neurol 5: 349-356, 2003.
  • Aminoff M: Neurology and General Medicine, 3rd ed. Philadelphia, Churchill-Livingstone, 2001.
  • Noseworthy JH (ed): Neurologic Therapeutics. London, Martin Dunitz, 2003.
  • Bradley WG, Daroff RB, Fenichel GM, Jankovic J: Neurology in Clinical Practice, 4th ed. Philadelphia, Butterworth-Heinemann, 2004.
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  • Samuels MA, Feske S (eds): Office Practice of Neurology, 2nd ed. Boston, Churchill-Livingstone, 2003.
  • Johnson RT, Griffin JW: Current Therapy in Neurologic Disease, 6th ed. St. Louis, Mosby, 2002.
  • Rolak LA (ed): Neurology Secrets, 4th ed. Philadelphia, Hanley & Belfus, 2005.

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