Polymyositis and dermatomyositis (DDX (pmr, , endocrine/metabolic myopathy…
Polymyositis and dermatomyositis
Rare conditions characterized by insidious onset of progressive symmetrical proximal muscle weakness and autoimmune-mediated striated muscle inflammation (myositis)
associated with myalgia ± arthralgia
Muscle weakness may also cause dysphagia, dysphonia (ie poor phonation, not dysphasia), or respiratory weakness
The myositis (esp. in dermatomyositis) may be a paraneoplastic phenomenon
commonly from lung, pancreatic, ovarian, or bowel malignancy.
Screen for cancers
Myositis plus skin signs:
• Macular rash (shawl sign is +ve if over back and shoulders).
• Lilac-purple (heliotrope) rash on eyelids often with oedema
• Nailfold erythema (dilated capillary loops).
• Gottron’s papules:
also seen on elbows and knees
(pathognomonic if ↑ck + muscle weakness).
roughened red papules over the knuckles,
Malignancy in 30% cases.
In both conditions include
interstitial lung fibrosis
myocardial involvement (myocarditis, arrhythmias).
muscle biopsy confirms diagnosis (and excludes mimicking conditions)
mri shows muscle oedema in acute myositis
emg shows characteristic fibrillation potentials
anti-mi2, anti-jo1—associated with acute onset and interstitial lung fibrosis that should be treated aggressively.
Muscle enzymes (alt, ast, ldh, ck, & aldolase) ↑ in plasma
endocrine/metabolic myopathy (eg steroids),
infection (eg hiv),
drugs (penicillamine, colchicine, statins, or chloroquine).
Immunosuppressives and cytotoxics are used early in resistant cases
Hydroxychloroquine/topical tacrolimus for skin disease.