Polymyositis and dermatomyositis

Question 1

Presentation of polymyositis

Answer 1

proximal shoulders - difficulty in raising arms above head

proximal thighs - difficulty in getting out of a chair/going upstairs

distal weakness - may also have reduced sensation - peripheral neuropathy

• double vision
• dysphonia
• dysphagia
• shortness of breath
• muscle wasting

Question 2

Polymyositis

Answer 2

Muscle weakness due to striated muscle inflammation – symmetrical, diffuse, starts proximally

SOB due to diaphragmatic weakness

Myalgia in 50%

Photosensitive rash - generally occurs before the weakness

Question 3

Dermatomyositis rash

Answer 3

Gottron’s papules

Heliotrope rash around the eyes

Question 4

Investigations

Answer 4

MSK examination 
Basic observations 
Bloods - CRP, CK, Ab
Electromyogram
Muscle or skin biopsy

Question 5

Auto antibodies

Answer 5

ANA

Anti-Jo-1

Question 6

Muscle biopsy of dermatomyositits

Answer 6

Vasculitis

Myofiber necrosis and atrophy at the periphery of fascicles (perifascicular atrophy

Question 7

Muscle biopsy of polymyositis

Answer 7

Endomysial cellular infiltrates

Fibre necrosis may be seen

Question 8

Mx

Answer 8

Treat with corticosteroids

Immunosuppressive agents – methotrexate, azathioprine, cyclophosphamide

Strong association with many malignancies- screening needed

Question 9

Dermatomyositis

Answer 9

Myositis + skin signs

• Gottron’s papules
• macular rash