Polymyositis, Dermatomyositis

Question 1

What is polymyositis?

What is dermatomyositis?

Answer 1

• Polymyositis= autoimmune disorder where there is chronic inflammation of muscles
• Dermatomyositis= autoimmune disorder where there is chronic inflammatino of muscles and skin

Question 2

What is the key invesigation for diagnosing polymyositis and dermatomyositis?

What is the approximate level in each disease?

Answer 2

• Creatine kinase
• Polymyositis usually <300U/L
• Dermatomyositis usually >1000U/L

Question 3

State some other causes of raised creatine kinase

Answer 3

• Rhabdomyolysis
• AKI
• Statins
• MI
• Strenuous exercise

Question 4

Polymyostis and dermatomysitis can be caused by underlying malignancy; true or false?

Answer 4

True (hence they are paraneoplastic syndromes). Most common associations are lung, breast, ovarian and gastric

Question 5

Describe the presentation of polymyositis

Answer 5

• Muscle pain (myalgia)
• Fatigue
• Weakness

Bilaterally, typically affects proximal muscles, mostly affects shoulders & pelvic girdle, develops over weeks.

NO SKIN FEATURES IN POLYMYOSITIS

Question 6

Describe the presentation of dermatomyositis

Answer 6

• Muscle pain (myalgia)
• Fatigue
• Weakness

Bilaterally, typically affects proximal muscles, mostly affects shoulders & pelvic girdle, develops over weeks

Dermatomyositis also has skin features:

• Gottron lesions
• Photosensitive erythematous rash on back, shoulders & neck
• Purple rash on face & eyelids
• Periorbital oedema
• Subcutaneous calcinosis

Question 7

What are gottron lesions?

Answer 7

Scaley erythematous patches on knuckles, elbows & knees

Question 8

What antibodies are present in:

• Polymyositis
• Dermatomyositis

Answer 8

• Polymyositis= anti-Jo-1
• Dermatomyositis=
  • anti-Mi-2
  • anti-nuclear antibodies
  • anti-Jo-1 (often present also)

Question 9

How is polymyositis and dermatomyositis diagnosed?

Answer 9

• Clinical presentation
• Eleveated CK
• Autoantibodies
• EMG
• Muscle biopsy to establish definitive diagnosis

Question 10

Discuss the management of polymyositis & dermatomyositis

Answer 10

• New cases should be assessed for underlying cancer

Conservative

• Physiotherapy to strengthen muscles
• Occupational therapy to help with ADLs/function

Pharmacological

• First line= steroids
• Other options:
  
  • Immunosupressants e.g. azathioprine
  • IV immunoglobulins
  • Biological therapies e.g. infliximab