Polymyositis

Question 1

What is polymyositis?

Answer 1

An idiopathic inflammatory myopathy that causes symmetrical, proximal muscle weakness.

Question 2

Pathogenesis of polymyositis

Answer 2

T-cell medicated cytotoxic process directed against unidentified muscle antigens. CD8 T cells, along with macrophages, surround healthy nonnecrotic muscle fibres and eventually invade and destroy them.

Question 3

Presentation of polymyositis

Answer 3

Symmetrical, proximal muscle weakness in upper and lower extremities
Insidious onset
Difficulty with particular activities
Some patients have myalgia
Dysphagia in 1/3 of patients (poor prognostic sign)
ILD in 5-30% of patients

Question 4

Polymyositis investigations

Answer 4

Raised inflammatory markers
Raised CK (more than 10 times the normal level)
ANA, anti-Jo-1 and Anti-SRP positive
MRI to localise extent of muscle involvement
Electromyographic (EMG) findings in 90% of patients.
Muscle biopsy = diagnostic

Question 5

Management of polymyositis

Answer 5

Prednisolone 40mg

Immunosuppressive drugs i.e. methotrexate or azathioprine