Therapy of polymyositis, dermatomyositis and inclusion-body myositis

Polymyositis, dermatomyositis and inclusion-body myositis are a group of aquired, and potentially treatable myopathies. The exact diagnosis is necessary, because the different forms differ with respect to therapeutical regimens. Diagnosis requires the combined results of clinical data, laboratory abnormalities, characteristic electromyographic changes and histopathological changes in muscle biopsy. Problems in diagnosis may arise when patients were treated with immunosuppressive drugs before muscle biopsy is obtained. The first-line drug for dermatomyositis and polymyositis are corticosteroids. Whereas dermatomyositis and polymyositis mostly improve upon corticosteroids in combination with another immunosuppression, inclusion-body myositis is characterized by a poor response to this medication. In cases not responding to this therapy immunglobulines can be administred. In dermatomyositis the effectiveness of immunglobulines is well documented by a double-blind study. In polymyositis, no controlled studies have been completed. In inclusion-body myositis, an attempt with immunglobulines is justified.