Dermatomyositis

 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

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