Polymyositis

Question 1

Definition of polymyositis

Answer 1

Inflammatory disorder causing symmetrical, proximal muscle weakness

Question 2

Pathophysiology of polymyositis

Answer 2

-Thought to be a T-cell mediated cytotoxic process directed against muscle fibres
-May be idiopathic or associated with connective tissue disorders
-Associated with malignancy

Question 3

Epidemiology of polymyositis

Answer 3

Typically affects middle-aged, female:male 3:1
-Age >40
-Exposure to high intensity of global UV radiation

Question 4

Clinical presentation of polymyositis

Answer 4

-Proximal muscle weakness +/- tenderness
-Raynaud’s
-Respiratory muscle weakness
-Interstitial lung disease= e.g. fibrosing alveolitis or organising pneumonia
-Dysphagia, dysphonia

Question 5

Investigations of polymyositis

Answer 5

-Elevated creatine kinase
-Other muscle enzymes (lactate dehydrogenase (LDH), aldolase, AST and ALT) are also elevated in 85-95% of patients
-EMG
-Muscle biopsy
-Anti-synthetase antibodies
=anti-Jo-1 antibodies are seen in pattern of disease associated with lung involvement, Raynaud’s and fever

Question 6

Management of polymyositis

Answer 6

-High-dose corticosteroids tapered as symptoms improve
-Azathioprine, methotrexate, mycophenolate may be used as a steroid-sparing agent