Makindo Medical Notes.com

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 a vasculopathy
• 10% association with malignancy - lung, breast, ovary, gut
• Cancers occur within the first 5 years after symptom onset.

Dermatomyositis unlike polymyositis has a heliotrope (purple) discoloration of the eyelids and scaly erythematous plaques over the knuckles (Gottron’s papules). It is associated with an increased incidence of underlying malignancy.

Epidemiology

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

Associated Malignancies

• Nasopharyngeal carcinoma
• Ovarian cancer and Breast cancer
• Gastric and Colon Cancer and Lung cancer
• Melanoma, non-Hodgkin lymphoma (NHL)

Clinical

• Symmetrical Muscle weakness is proximal and progressive
• Muscles may be swollen and tender, arthralgia, weight loss
• Scaly red palpable rash over MCP or IP joints suggests
• Periorbital oedema and purplish discolouration "Heliotrope" rash.
• Rash over the knuckles and is called "Gottron's sign"
• Rash on shoulders and back. The shawl sign V type erythematous rash
• Hands: "mechanic's hands," rough, cracked skin tips of the fingers
• Interstitial lung disease and weakness of respiratory muscles
• Photosensitive rashes are common, Nail fold telangiectasia

Investigations

• FBC: anaemia, raised/normal ESR
• ↑↑ CK (x 50-fold), LDH and AST suggests myositis
• Muscle biopsy: chronic inflammatory changes, muscle fibre necrosis
• Skin biopsy: interface dermatitis, atrophy of epidermis, perivascular lymphocytic infiltrate in the dermis
• MRI can show inflamed muscle
• EMG: fibrillation potentials, short duration low amplitude polyphasic potentials, bizarre high frequency discharges
• ANA +ve in 80% but more specific is Positive anti-Jo-1 is more strongly associated with acute onset myositis, interstitial lung disease, fever, arthritis, Raynaud's phenomenon, mechanic's hand's appearance
• Anti-SRP (signal recognition particle)
• Screening for occult malignancy

Management

• Expert involvement of Rheumatology
• Steroids Prednisolone 0.5-1mg/kg and then slowly tapered down. CK falls rapidly but muscle strength takes weeks to improve
• Methotrexate, Azathioprine, Mycophenolate

References

• Dermatomyositis at BMJ