Polymyositis

Question 1

What is polymyositis

Answer 1

Idiopathic inflammatory autoimmune myopathy - symmetrical proximal muscle weakness and inflammation

Question 2

Cause of polymyositis

Answer 2

Genetic factors - HLA-DR3 + HLA-DR7
Viral infections picornaviridae and retroviridae families
Drugs, UV raditation + exposure to some chemicals

Question 3

Pathophysiology of polymyositis

Answer 3

Cytokine and Chemokine Release: In response to muscle injury, a variety of pro-inflammatory cytokines and chemokines are released, recruiting additional immune cells to the site of injury and perpetuating the inflammatory cycle.

Muscle Fibre Damage and Regeneration: As a consequence of the ongoing inflammation, muscle fibres undergo necrosis. Satellite cells, muscle progenitor cells, are activated in an attempt to regenerate muscle tissue. However, with persistent inflammation, this reparative process is overwhelmed, leading to muscle atrophy and fibrosis.

Question 4

Features of polymyositis

Answer 4

Prgressive Proximal musle weakness/tenderss - predominantly shoulder and pelvic girdles
ARTHRALGIAS
Raynauds
Resp muscle weakness
ILD - fibrosing alveolitis or organsing pneumonia
Dysphagia, dysphonia

Question 5

Investigations for polymyositis

Answer 5

Elevated CK,LHD
EMG
muscle biopsy
Antibodies - Jo-1

Question 6

When are anti Jo-1 antibodies seen in polymyositis

Answer 6

With lung ivolvement, raynauds and fever

Question 7

Antibodies seen in polymyositis

Answer 7

Anti-synthetase antibodies
Anti-Jo-1

Question 8

Management of polymyositis

Answer 8

Immunosupression - corticosteroids
Refractory or severe (ILD, rapid) -> azathioprine or methotrexate
IV IG and rituximab if intolerant or refractor