Inclusion body myositis | Polymyositis | |
Sex | Male > female | Female > male |
Age | Uncommon before 50 | Common before 50 |
Onset | Insidious | Acute or subacute |
Course | Slowly progressive | More rapid |
Distribution of weakness | Usually asymmetric finger flexor and proximal leg weakness | Proximal, symmetric |
Creatine kinase | Normal or <10x normal | Often >10x normal |
EMG | Myopathic or mixed myopathic and neurogenic | Myopathic |
Muscle biopsy | Inflammation, rimmed vacuoles, inclusions, p62 + inclusions, cytochrome oxidase negative fibers | Inflammation, fiber necrosis |
Response to therapy | Generally poor | Expected |
Autoantibodies | Anti-cytosolic 5' nucleotidase IA (NT5C1A) | No specific autoantibodies |
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