Dermatomyositis and polymyositis

Question 1

what are they?

Answer 1

rare idiopathic muscle diseases that are characterised by inflammation of striated muscles

age of onset 40-50

Question 2

what are the signs and symptoms?

Answer 2

insidious onset of muscle proximal weakness, often painless

presentation may be with shortness of breath or with rash

raynauds syndrome is common

Question 3

what is the diagnostic criteria?

Answer 3

• symmetrical proximal muscle weakness
• raised serum muscle enzyme levels
• typical electromyographic (EMG) changes
• biopsy evidence of myositis
• typical rash of dermatomyositis
• Polymyositis if >=3 of the first 4 above criteria
• dermatomyositis if rash and >=2 of the first 3 above criteria

Question 4

what investigations are done?

Answer 4

• may have raised inflammatory markers
• FBC is usually normal
• kidney unaffected
• raised ALT( from muscle) with the liver enzymes normal may be a clue
• 80% patients are ANA positive
• myositis is well demonstrated on MRI
• specific auto- antibodies are being discovered and include anti-JO-1 and anti-Mi2

Question 5

what is the treatment?

Answer 5

• high dose corticosteroids is the mainstay in the first few weeks
• monitor disease with inflammatory markers and CK
• repeat MEG studies/MRI or biopsy may be needed
• long term control with methotrexate or azathriopine. Rituximab can be affective
• intravenous immunoglobulin also affective
• in dermatomyositis, sun protection is important

Question 6

how can these conditions lead to respiratory failure?

Answer 6

diaphragmatic involvement may lead to respiratory failure

Question 7

how can these conditions cause aspiration pneumonia?

Answer 7

The upper oesophagus has striated muscle so swallowing may be affected, with a risk of aspiration pneumonia