Makindo Medical Notes

Related Subjects: |Relapsing Polychondritis |Reactive Arthritis |Raynaud's Phenomenon |Polymyositis |Dermatomyositis |Polyarteritis nodosa |Osteoporosis |Rheumatoid Arthritis |Systemic Sclerosis (Scleroderma) |Rheumatology Autoantibodies |Overlap Syndrome

Dermatomyositis is a multi-organ idiopathic inflammatory disorder characterized by proximal skeletal muscle weakness, muscle inflammation, and distinct skin manifestations. In summary: Myositis + Rash +/- cancer.

About

• Idiopathic inflammatory myositis with an associated vasculopathy.
• 10% association with malignancy, including cancers of the lung, breast, ovary, and gut.
• Malignancies typically occur within the first 5 years after the onset of symptoms.

Dermatomyositis, unlike polymyositis, presents with heliotrope (purple) discoloration of the eyelids and scaly erythematous plaques over the knuckles (Gottron’s papules). It has an increased association with underlying malignancies.

Epidemiology

• Most commonly seen in females between 40-50 years old.
• Positive anti-Jo-1 antibody is often found in cases.

Associated Malignancies

• Nasopharyngeal carcinoma.
• Ovarian cancer and breast cancer.
• Gastric, colon, and lung cancer.
• Melanoma, non-Hodgkin lymphoma (NHL).

Clinical Features

• Symmetrical muscle weakness, proximal and progressive.
• Muscles may be swollen and tender, often associated with arthralgia and weight loss.
• Scaly red palpable rash over MCP or IP joints suggests dermatomyositis.
• Periorbital oedema and purplish discoloration: "Heliotrope" rash.
• Rash over the knuckles known as "Gottron's sign".
• Rash on shoulders and back, described as the "shawl sign" or V-type erythematous rash.
• Hands may exhibit "mechanic's hands"—rough, cracked skin at the tips of the fingers.
• May be associated with interstitial lung disease and weakness of respiratory muscles.
• Photosensitive rashes and nail fold telangiectasia are common.

Investigations

• FBC: May show anaemia, raised/normal ESR.
• ↑↑ CK: Elevated creatine kinase (up to 50-fold), LDH, and AST indicate myositis.
• Muscle biopsy: Shows chronic inflammatory changes and muscle fibre necrosis.
• Skin biopsy: May reveal interface dermatitis, epidermal atrophy, and perivascular lymphocytic infiltrate in the dermis.
• MRI: Can detect inflamed muscles.
• EMG: Fibrillation potentials, short-duration low-amplitude polyphasic potentials, and bizarre high-frequency discharges.
• Autoantibodies:
  • ANA: Positive in 80% of cases.
  • Anti-Jo-1: Associated with acute onset myositis, interstitial lung disease, fever, arthritis, Raynaud's phenomenon, and "mechanic's hands".
  • Anti-SRP: Signal recognition particle antibodies, associated with severe disease.
• Screening for occult malignancy is recommended due to the strong association with cancers.

Management

• Rheumatology involvement: Expertise in managing complex cases is essential.
• Steroids: Prednisolone 0.5-1 mg/kg, tapered gradually. CK levels fall rapidly, but muscle strength recovery may take weeks.
• Immunosuppressants: Methotrexate, azathioprine, or mycophenolate can be used in severe or resistant cases.

References

• Dermatomyositis at BMJ