Dermatomyositis And Polymyositis – Diagnosis

Posted by Alex

Patients with dermatomyositis who have the characteristic skin rash, muscle weakness, EMG changes, and elevation of serum CK may not require a muscle biopsy to confirm the diagnosis. In the case of idiopathic polymyositis, however, a firm diagnosis must be based on the presence of a typical clinical picture, a typical EMG, elevation of serum CK, and a diagnostic muscle biopsy. All four of these criteria are required to be certain of the diagnosis, since inflammatory changes may occasionally occur in other myopathies (e.g., facioscapulohumeral muscular dystrophy) and in other connective tissue disorders without clear muscle weakness. However, in fewer than one-third of cases of polymyositis are ALL these criteria satisfied. It may be particularly difficult to obtain a diagnostic muscle biopsy because of the patchy nature of the disease. Thus, a therapeutic trial of glucocorticoids should be given when full investigation of a patient with significant disability leaves a diagnosis of “possible polymyositis,” usually because of a nondiagnostic muscle biopsy.