Dermatomyositis

Bohan et al used five major criteria to define polymyositis and dermatomyositis: (1) symmetrical weakness of the limb-girdle muscles and anterior neck flexors, with or without dysphagia or respiratory muscle involvement; (2) muscle biopsy evidence of myositis and necrosis of muscle; (3) elevation of level of skeletal muscle enzyme activity in serum; (4) electromyographic triad of (a) short polyphasic motor units, (b) fibrillations, positive sharp waves, and insertional irritability, and (c) bizarre, high-frequency repetitive discharges; and (5) dermatologic features consisting of (a) heliotrope rash (periorbital lilac discoloration with edema), (b) Gottron's sign (scaly erythematous dermatitis over dorsum of hands, especially metacarpophalangeal and proximal interphalangeal joints, and (c) involvement of knees, elbows, medial malleoli, face, neck, and upper torso.