Dermatomyositis and Polymyositis

Question 1

What is dermatomyositis?

Answer 1

Inflammtry muscle disease associated with skin changes

Question 2

What is polymyositis?

Answer 2

Inflammation of striated muscle fibres

Question 3

What are the symptoms of polymyositis?

Answer 3

Proximal muscle weakness
Fever
Arthralgia
Raynaud’s

Question 4

What are the symptoms of dermatomyositis?

Answer 4

Proximal muscle weakness 
Macular rash 
Lilac rash on eyelids
Nail-fold erythema 
Gottron's papules

Question 5

What are Gottron’s papules?

Answer 5

Linear papules on knuckles

Question 6

What are the diagnostic criteria?

Answer 6

Symmetrical proximal muscle weakness
Raised serum ALT or CK 
Typical EMG changes 
Biopsy evidence of myositis
Typical rash of dermatomyositis

Polymyositis = >/=3 of first 4
Dermatomyositis = >/=2 of first 3 + rash

Question 7

What are the typical EMG changes?

Answer 7

Fibrillation potentials

Question 8

What investigations should you do?

Answer 8

Bloods

• FBC (usually normal)
• LFTs ( raised ALT with others all normal)
• CPK (raised)

EMG

Autoantibodies

• anti-Jo-1
• anti-Mi2

Muscle biopsy

Question 9

What is the management?

Answer 9

High dose corticosteroids

Long term = methotrexate/azathioprine