Polymyositis and Dermatomyositis

Question 1

difference between polymyositis and dermatomyositis?

Answer 1

These are autoimmune disorders where there is inflammation in the muscles (myositis). Polymyositis is a condition of chronic inflammation of muscles. Dermatomyositis is a CTD where there is chronic inflammation of the skin and muscles.

Question 2

what is CK, why is it used in polymyositis and dermatomyositis?

Answer 2

• This is the key investigation for myositis
• CK is an enzyme found inside muscle cells.
• Inflammation in the muscle cells (myositis) leads to release of CK.
• CK is usually less than 300 U/L.
• In polymyositis and dermatomyositis, result is usually >1000.

Question 3

what other things can cause a raised CK?

Answer 3

• Rhabdomyolysis
• AKI
• MI
• Statins
• Strenuous exercise.

Question 4

what should we worry about when a pt presents with dermatomyositis or polymyositis?

Answer 4

Polymyositis and dermatomyositis can be caused by underlying malignancy as they are paraneoplastic syndromes. Most commonly associated with: lung, breast, ovarian, gastric.

Question 5

how would a polymyositis/dermatomyositis pt present ?

Answer 5

Presentation

• Muscle pain, fatigue, weakness
• Occurs bilaterally and typically affects proximal muscles
• Mostly affects shoulders and pelvic girdle
• Develops over weeks.

Question 6

whar are skin features you would find in dermatomyositis?

Answer 6

1) Gottron lesions (scaly erythematous patches) on knuckles, elbows and knees.
2) Photosensitive erythematous rash on back, shoulders and neck.
3) Purple rash on face and eyelids
4) Periorbital oedema
5) Subcutaneous calcinosis

Question 7

what antibodies would you test for in polymyositis or dermatomyositis?

Answer 7

1) Anti-jo-1 (polymyositis but can be present in dermatomyositis)
2) Anti-Mi-2 (dermatomyositis)
3) Anti-nuclear Antibodies (dermatomyositis)

Question 8

what Ix might you use to make a diagnosis of dermatomyositis or polymyositis ?

Answer 8

1) Clinical presentation
2) Elevated CK
3) Autoantibodies
4) EMG (electromyography)
5) Muscle biopsy can be used to establish a definite diagnosis

Question 9

how is polymyositis/ dermatomyositis managed?

Answer 9

• Guided by a rheumatologist
• Need to investigate for underlying cancer
• May require physio and OT to help muscle strength and function
• Corticosteroids are the first line treatment of both conditions
• May require:
  Immunosuppressants (azathioprine)
  IV immunoglobulins
  Biological therapy (infliximab or etanercept)