Table 1.

The Bohan and Peter criteria for DM and PM [1, 2]

First, rule out all other forms of myopathies

1. Symmetrical weakness, usually progressive, of the limb-girdle muscles with or without dysphagia and respiratory muscle weakness

2. Muscle biopsy evidence of myositis

Necrosis of type I and type II muscle fibers; phagocytosis, degeneration, and regeneration of myofibers with variation in myofiber size; endomysial, perimysial, perivascular, or interstitial mononuclear cells.

3. Elevation of serum levels of muscle-associated enzymes (CK, LDH, transaminases, aldolase)

4. EMG triad of myopathy

a. Short, small, low-amplitude polyphasic motor unit potentials

b. Fibrillation potentials, even at rest

c. Bizarre, high-frequency repetitive discharges

5. Characteristic rashes of dermatomyositis

Definite PM: all first four elements, probable PM: 3 of first 4, possible PM: 2 of first 4. Definite DM: rash plus 3 others, probable DM: rash plus 2 others, possible DM: rash plus 1 other

CK, creatinine kinase; LDH, lactate dehydrogenase; EMG, electromyography; PM, polymyositis; DM, dermatomyositis