Polymyositis is an idiopathic inflammatory disorder of skeletal muscle. When it is associated with cutaneous lesions it is dermatomyositis.
Features:
- Progressive proximal muscle weakness
- Dysphonia
- Dysphagia
- Fever
- Arthralgia/arthritis
- Muscle pain
- More rarely respiratory muscle weakness
Possible complications:
- Cardiomyopathy
- Intersitial lung disease
- Malignancy – commonest in dermatomyositis; most frequently lymphoma or ovarian or gastric cancer
Skin signs:
- Pathognomonic
- Gottron’s papules = erthematous papules over IP/MCP/elbow/knee joints
- Gottron’s sign = macules/plaques in same distribution as Gottron’s papules
- Non-pathognomic signs
- Heliotrope (liliac-purple) rash around eyelids/cheeks
- Shawl sign = macular rash over back and shoulders
- Periungal telangectasia
Investigations
- Raised CK/AST/ALT/LDH
- Raised ANA in 60-80%
- Anti-Jo antibodies in 20% of dermatomyositis
- Abnormal EMG
Treatment is:
- Prednisolone
- Methotrexate/cyclosporin
- Screen for malignancy
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