Clinical features:
- Heliotrope ‘lilac/purple blue’ rash around the eyelids, malar region, extensors, knuckles, trunk
- Gottron’s papules on hand dorsum
- Nailfold telangiectasia & erythema
- Nail changes; thickening, cracking
- Proximal Muscle weakness
Findings on investigations:
Nerve conduction studies/electromyography NCS/EMG:
MUAP Myopathic recruitment On activation: Short duration, low amplitude polyphasic units
Spontaneously: increased activity with fibrillations, complex repetitive charges & positive sharp waves
Muscle Biopsy, is diagnostic:
- Myofibres: Perifascicular atrophy (myofibres at the periphery of the fascicle). ‘punched out’ vacuoles. Microinfarcts (contiguous necrotic or regenerating fibres.
- Inflammation: Perivascular, interfascicular/septal, endomysial. Mainly lymphocytes but plasma cells & eosinophils occur. Perivascular lymphocytes in capillaries DDx.
- Systemic vasculitis involves larger arteries.
- Immunohistochemistry: T cells & B cells in lymphocytes, complement activation on capillaries
Notes:
- 15% of dermatomyositis is a/w neoplasia:
- Ovarian, breast, melanoma, colon cancer
- Dermatomyositis may affect children,
- CK, follows disease activity: Elevated or normal
Other tests:
Anti-Mi-1 antibodies, anti-Mi-2 antibodies
Findings on investigations:
- FBC, blood chemistry panel,
- CK: usually increased, marker of activity
- Antibodies:
- Anti-Jo-1: dermatomyositis or polymyositis
- Anti PM/Scl: polymyositis systemic sclerosis overlap syndrome
Search for neoplasm in dermatomyositis:
- CT thorax abdomen & pelvis
- Colonoscopy
Monitor:
- Pelvic, breast, rectal examinations
- Weakness not CK
Treatment:
General measures:
- Physical therapy to prevent contractures
- Rest during exacerbations
Glucocorticoids:
- Prednisolone +/- potassium supplements +/- antacids
- High dose, then taper over 10 weeks, Maintenance for 2-3 yrs
If resistant (>3 months on glucocorticoids) or rapid:
- Azathioprine P.O.
- Methotrexate weekly
Other options:
- Intravenous immunoglobulin IVIg
- Cyclophosphamide, ciclosporin or mycophenolate
Treat the underlying tumour if one is present
Causes of dermatomyositis:
Idiopathic
Secondary:
- Neoplasia in 15%:
- Ovarian, breast, melanoma, colon cancer
- Penicillinamine
- Overlap syndrome with other connective tissue disease
- Associates vasculitis in children