Background Definition

Dermatomyositis is one of the idiopathic inflammatory myopathies.1-3 In a set of criteria to aid in the diagnosis and classification of dermatomyositis and polymyositis, first proposed in 1975 by Bohan and Peter,4 four of the five criteria are related to the muscle disease:

1. Progressive proximal symmetrical weakness

2. Elevated muscle enzymes

3. Abnormal electromyogram (EMG)

4. Abnormal muscle biopsy

5. Presence of compatible cutaneous disease

It has subsequently been recognised that there are many patients with compatible cutaneous disease who do not have initial manifestations of their muscles as defined by clinical weakness and elevated enzymes. Some of these patients have subtle changes on biopsy, EMG or magnetic resonance imaging studies at diagnosis; some develop these changes and possibly clinical manifestations later, while a small group of patients never seem to develop clinical muscle disease. Sontheimer5 has used the term "amyopathic dermatomyositis" for those patients without muscle weakness and with normal muscle enzymes for at least 2 years in the absence of disease modifying therapies such as corticosteroids and/or immunosuppressive agents.

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