Polymyositis and Dermatomyositis - Connective Tissue Diseases

Polymyositis and Dermatomyositis

·        Peaks in age 10-14 (mainly dermatomyosis) and 45 – 60 years (mainly polymyositis).

·        Presentation: 

o  Voluntary muscle inflammation ® insidious, symmetrical, proximal muscle weakness (shoulders, hips, trunk, neck – compared to polymyalgia rheumatica which just has stiffness). May ® atrophy and contractures 

o  Skin (only Dermatomyositis): Gottron‟s lesions: erythematous plaques or macules over MCP joints, extensor knees, wrist and elbows. Rash over upper chest, neck, etc

o  Other symptoms: Fatigue, malaise, weight loss, fever

o  Causes dysphagia, dysphonia, facial oedema, respiratory weakness 

o  Also Raynaud‟s, lung involvement (interstitial fibrosis), polyarthritis, retinitis, myocardial involvement, purple rash on cheeks and light exposed areas

·        Differential Diagnosis:

o  Infection

o  Muscular dystrophy 

o  Endocrine: thyroid, PTH, ­Ca, ¯K

o  Neurology: motor neurone, Guillian Barre, Myasthenia Gravis

o  Drugs

·        Investigations: 

o  ­ESR, CRP, CK, maybe ­AST and LD

o  RF positive in 50%

o  ANA may be +ive, as well as myositis specific antibodies (eg AntiJo-1 – linked to HLA DR3) 

o  EMG ® denervation and myopathy (not usually done)

o  Biopsy: inflammatory muscle infiltrate + fibrosis

·        Associations:

o  Other autoimmune rheumatological diseases

o  Malignancy in 10%

o  Coxsackie virus, rubella & influenzae

·        Diagnosis of exclusion

·        Treatment: rest, steroids, methotrexate, Ig, active graded exercise between attacks