Table 1: Bohan and Peter diagnostic criteria for dermatomyositis/polymyositis.

(1) Symmetrical weakness of limb-girdle muscles and anterior neck flexor
(2) Muscle biopsy shows evidence of characteristic myositis
(3) Elevated serum skeletal muscle specific enzyme, especially creatinine phosphokinase
(4) Electromyographic (EMG) evidence of myositis
(5) Typical dermatomyositis rash, including heliotrope and Gottron’s papules

Definite polymyositis: all of items (1)–(4); probable: any three of items (1)–(4); possible: any two of items (1)–(4).
Definite dermatomyositis: item 5 plus any three of items (1)–(4); probable: item 5 plus any two of items (1)–(4); possible: item 5 plus any one of items (1)–(4).