Inflammatory myopathy with skin manifestations
Affects proximal muscles > distal
Female:Male; 2:1
Peak incidence 40-50s
Juvenille<unk> : 5-10 years of age
Dermatomyositis
Infection:
Polymyositis
Viral infection 
Pyomyositis
Bacterial infection
Lambert-Eaton myasthenic syndrome
Spirochete infection 