Age of onset of first symptom
0 – 17
18 – 39
40+
Objective symmetric weakness, usually progressive, of the proximal upper extremities
Objective symmetric weakness, usually progressive, of the proximal lower extremities
Neck flexors are relatively weaker than neck extensors
In the legs proximal muscles are relatively weaker than distal muscles
Heliotrope rash
Gottron's papules
Gottron's sign
Dysphagia or esophageal dysmotility
Anti-Jo-1 (anti-Histidyl-tRNA synthetase) autoantibody positivity
Elevated serum levels of creatine kinase (CK) or lactate dehydrogenase (LDH) or aspartate aminotransferase (ASAT/AST/SGOT) or alanine aminotransferase (ALAT/ALT/SGPT)
Endomysial infiltration of mononuclear cells surrounding, but not invading, myofibers
Perimysial and/or perivascular infiltration of mononuclear cells
Perifascicular atrophy
Rimmed vacuoles