idiopathic inflammatory myopathies Flashcards
definition of idiopathic primary inflammatory myopathies
myopathies characterised by chronic inflammation of striated muscle (polymyositis and inclusion body myositis) and skin (dermatomyositis)
aetiology of idiopathic inflammatory myopathies
unknown
maybe autoimmune
maybe infective or malignancy trigger in genetically predisposed individual
inflammation around blood vessels
RF of idiopathic inflammatory myopathies
polymyositosis - autoimmune connective tissue disorders eg scleroderma
dermatomyositis - bronchial, stomach, breast and ovarian malignancy and auto-Ab anti-Jo-1, anti-Scl, anti-Mi2, HLA linkage to DRW52
epidemiology of idiopathic inflammatory myopathies
rare
0.2-1/100000
5-15yrs and 40-60yrs
inclusion body myositis most common >50yrs
symptoms of idiopathic inflammatory myopathies
fatigue
malaise
dyspnoea
myalgia and arthralgia can occur
skin rash, raynauds
symptoms of polymyositis and dermatomyositis
gradual onset 3-6mo of progressive painless prox muscle weakness (difficulty raising objects above head, rising from chair, climbing stairs)
can hvae dysphagia and dysphonia
symptoms of inclusion body myositis
insidious onset (mo-yr)
affectes rising from chair and dexterity of hands
may be dysphagia and neck droop
signs of polymyositis and dermatomyositis
- prox muscle weakness and atrophy affecting upper and lower limbs
- skin lesions in dermatomyositis
- associated with myalgia +- arthralgia, or resp weakness
- fever
- raynauds
- interstitial lung fibrosis
- myocardial involvement - myocarditis, arrhythmias
- calcinosis in skin
describe the skin lesions in dermatomyositis
macular lilac heliotrope rash on upper eyelids and forehead with periorbital oedema
macular rash on chest wall, neck, elbows or knees - shawl sign positive if over back and shoulders
gottrens papules - scaly erythematous raised plaques on finger joints elbows and knees, periungal telangiectasia, ragged cuticles - pathonomonic if high CK and muscle weakness
mechanics hands - fissuring dermatitis of finger pads
nail fold erythema (dialted capillary loops)
grotton papules
signs of inclusion body myositis
prox and distal muscle weakness and atrophy - wrist and deep finger flexors, quadriceps
weakness of erector spinae and dysphagia is common
starts with quadriceps, finger flexors or pharyngeal muscles
ventral extremity muscle groups are more affected than dorsal or girdle groups
pathogenesis of polymyositis
cytotoxic CD8+ T cell infiltrate which appear to recognise an ag on muscle fibre surface
pathology of dermatomyositis
probably humorally mediated disorder with perivascular and perifascicular infiltrate in skeletal muscle
pathology of inclusion body myositis
T cell inflammatory infiltrate into the skeletal msucle suggests an immune basis
non-inflammed skeletal muscle fibres may contain rimmed vacuoles and amyloid deposits - suggesting a degenerative process
investigations for idiopathic inflammatory myositis
careful evaluation for underlying malignancy
blood:
- FBC - anaemia of chronic disease
- high ESR (can be normal)
- high CK, ALT, AST, LDH and aldolase (ie muscle enzymes)
- auto-Ab titres - anti-Mi2 and anti-Jo1 associated with acute onset and interstitial lung fibrosis that should be treated aggresively
EMG
- high insertional activity
- high spontaneous fibrillations
- abnormal low amplitude short duration polyphasic motor potentials and bozarre high frequency discharges indicative of myopathy
muscle biopsy
- required for definitive dx
- inclusion body myositis has typical features of inflammation as well as vacuolated uninflammed muscle fibres and amyloid deposits
CT or MRI
- look for malignancies
- MRI - muscle oedema in acute
- see muscle is white = inflammed
