polymyositis/dermatomyositis

polymyositis/dermatomyositis

Rheumatology An 'overlap' syndrome where polymyositis and dermatomyositis share multiple features–proximal distribution of muscle weakness, typical skin changes, 'machinist's hands', chronic 'round cell' inflammation, IgM rheumatoid factor, myopathic changes, spontaneous electrical discharges by EMG, response to corticosteroids. See Machinist's hands, Polymyositis.

Polymyositis-dermatomyositis–defining criteria

1.  Symmetric proximal/limb-girdle muscle weakness of insidious onset

2.  Typical skeletal pathology–eg, presence of 'skip' areas of involvement

3.  ↑ Serum levels of skeletal muscle enzymes–ALA, aldolase, AST, CK-MM, LDH

4.  A characteristic EMG triad of brief small polyphasic motor unit potentials, fibrillation potentials, positive waves, insertion irritability, and normal conduction velocity

Dermatomyositis is defined by a final criterion

5.  Lilac/heliotrope discoloration of eyelids, periorbital edema; characteristic scaling erythematous rash over dorsal aspect of hands–Gottron sign, involvement of elbows, knees, medial malleoli and upper body