• Skin biopsy may be helpful, although the histopathologic changes are consistent with, rather than diagnostic of, dermatomyositis.
- Serum levels of muscle enzymes are typically elevated, with the creatine phosphokinase (CPK) level the most reliable indicator of disease activity.
- An electromyogram of an affected muscle will generally be abnormal.
- Biopsy of an affected muscle may be diagnostic, but nonspecific changes are also seen. The use of magnetic resonance imaging has been reported recently to be helpful in identifying muscle groups that would most likely yield significant findings on muscle biopsy.
- Although many patients with dermatomyositis have a positive screening ANA, only a small percentage will have specific ANAs detected, such as anti–Jo-1 or anti–Mi-2.
Dunn CL, James WD: The role of magnetic resonance imaging in the diagnostic evaluation of dermatomyositis,
Arch Dermatol 129:1104–1106, 1993.
