Table 1.

Bohan and Peter’s polymyositis and dermatomyositis diagnostic criteria

1. Symmetric proximal muscle weakness determined by physical examination

2. Elevation of serum skeletal muscle enzymes, including CK, aldolase, serum glutamate oxaloacetate and pyruvate transaminases, and lactate dehydrogenase

3. The electromyographic triad of short, small, polyphasic motor unit potentials; fibrillations, positive sharp waves, and insertional irritability; and bizarre, high-frequency repetitive discharges

4. Muscle biopsy abnormalities of degeneration, regeneration, necrosis, phagocytosis, and an interstitial mononuclear infiltrate

5. Typical skin rash of DM. Including a heliotrope rash and Gottron’s sign/papules

The diagnosis of polymyositis is considered defined, probable and possible when 4, 3, or 2 muscle criteria are present, respectively

The diagnosis of dermatomyositis is considered definite, probable and possible when skin rash is associated with 3, 2, or 1 muscular criterion, respectively

Exclusion criteria: central or peripheral neurologic diseases, muscular dystrophies, granulomatous and infectious myositis, metabolic and endocrine myopathies, and myasthenia gravis