Tanimoto et al developed classification criteria for identifying patients with dermatomyositis and polymyositis. The authors were members of a task force formed by the Japanese Ministry of Health and Welfare and are from several universities in Japan.
Skin lesions:
(1) heliotrope rash (red-purple edematous erythema on the upper palpebra)
(2) Gottron's sign (red-purple keratosis, atrophic erythema, or macules on the extensor surface of finger joints)
(3) erythema on the extensor surface of extremity joints (slightly raised red-purple erythema over elbows or knees)
Other findings:
(1) proximal muscle weakness (upper or lower extremity and trunk)
(2) elevated serum creatine kinase (CK) or aldolase levels
(3) muscle pain on grasping, or spontaneous muscle pain
(4) myogenic changes on EMG (short duration, polyphasic motor unit potentials with spontaneous fibrillation potentials)
(5) positive anti-Jo-1 antibody (antibody to histadyl tRNA synthetase)
(6) nondestructive arthritis or arthralgias
(7) systemic inflammatory signs
(8) pathologic findings compatible with inflammatory myositis
Systemic inflammatory signs - one or more of the following:
(1) fever > 37°C at axilla
(2) elevated serum C-reactive protein (CRP)
(3) accelerated erythrocyte sedimentation rate (> 20 mm/h by the Westergren method)
Pathologic findings compatible with inflammatory myositis:
(1) inflammatory infiltration of skeletal muscle with degeneration or necrosis of muscle fibers
(2) active phagocytosis
(3) central nuclei
(4) evidence of active regeneration
Dermatomyositis:
(a) at least 1 skin lesion
(b) at least 4 of the other findings
Polymyositis:
(a) at least 4 of the other findings
Performance:
• The sensitivity of the criteria for dermatomyositis is 94%; and for polymyositis 99%.
• The specificity is 95%.
