Polymyositis

Question 1

pathogenesis

Answer 1

proposed - T cell mediated cytotoxic process directed against unidentified muscle antigens - CD8 T cells, macrophages surround healthy nonnecrotic muscle fibres

Question 2

what is it?

Answer 2

idiopathic inflammatory myopathy symmetrical, proximal muscle weakness

Question 3

how does it present?

Answer 3

symmetrical, proximal muscle weakness in the upper and lower limbs insidious onset difficulty with particular activities - e.g. climbing stairs some patients have myalgia dysphagia in 1/3 patients - secondary to oropharyngeal and oesophageal involvement - poor prognostic signILD in 5-30% of patients (especially Anti-Jo positive)raised inflammatory markers

Question 4

Investigations

Answer 4

raised inflammatory markers CK raised, often 10x normal immunology - ANA, anti-RNP: shared with other AI diseases - Anti-Jo-I, anti-SRP: unique to myositisMRI - localise extent of the muscle involvement - show signal intensity abnormalities of the muscle due to inflammation, oedema, scarring EMG - abnormal in 90% (staging)Muscle biopsy - crucial - excluding other rare muscle diseases - muscle fibres in varying stages of inflammation, necrosis and regeneration

Question 5

how is it managed?

Answer 5

prednisolone - 40mg initially combined with immunosuppressive drugs - methotrexate, azathioprine

Question 6

what is the prognosis?

Answer 6

usually responsive to treatment, albeit slowly 30% left with some residual weakness older patients and late presentation - do less well