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How does Inclusion Body Myositis differ from Polymyositis?
Despite IBM and PM both being inflammatory myopathies, there are several clinical and immunologic differences that distinguish between them
Inclusion Body Myositis versus Polymyositis
| Inclusion Body Myositis | Polymyositis | |
|---|---|---|
| Demographics | Male > Female, age >50 years | Female > Male, all ages |
| Muscle involvement | Proximal and distal Asymmetric | Proximal Symmetric |
| Other organ involvement | Neuropathy | Interstitial lung disease, arthritis, heart involvement |
| Antinuclear antibodies | Sometimes | Sometimes |
| Myositis-specific antibodies | No | Yes |
| Electromyogram | Myopathic and neuropathic | Myopathic |
| Muscle biopsy | CD8+T-cell infiltrate. Red-rimmed vacuoles, beta-amyloid | CD8+T-cell infiltrate |
| Response to immunosuppressive therapy | No | Frequent |
Pearl : A patient with PM who fails to respond to prednisone should be reexamined for IBM.
