24. Polymyositis and dermatomyositis

Question 1

What are polymyositis and dermatomyositis?

Answer 1

Rare conditions characterized by an onset of progressive symmetrical proximal muscle weakness as well as autoimmune-mediated muscle inflammation (myositis), associated with myalgia +/- arthralgia

• Muscle weakness may also cause dysphagia, dysphonia

Question 2

What is the etiology of polymyositis and dermatomyositis?

Answer 2

They may be paraneoplastic phenomenon, commonly from:

• Lung malignancy
• Pancreas malignancy
• Ovary malignancy
• Bowel malignancy

Question 3

What are the skin dermatomyositis symptoms?

Answer 3

Myositis + skin signs:

• Macular rash (shawl sign is positive if over back/shoulders)
• Lilac-purple (helitrope) rash on eyelids
• Nailfold erythema
• Gottron’s papules
• Subcutaneous calcifications

Question 4

What are the extramuscular symptoms of polymyositis and dermatomyositis?

Answer 4

• Fever
• Arthralgia
• Raynaud’s phenomenon
• Interstitial lung fibrosis
• Myocardial involvement (myocarditis, arrhythmias)

Question 5

Which tests are used to diagnose polymyositis and dermatomyositis?

Answer 5

• Muscle enzymes:
  
  • Increase of ALT, AST, LDH and CK in plasma
• EMG:
  
  • Shows characteristic fibrillation potentials
• Muscle biopsy:
  
  • Confirms diagnosis!!!!
• Autoantibody associations:
  
  • Anti-Mi2, anti-Jo1

Question 6

What is the differential diagnosis?

Answer 6

• Carcinomatous myopathy
• Inclusion-body myositis
• Muscular dystrophy
• Rhabdomyolysis
• Infection
• Drugs

Question 7

How can we manage polymyositis and dermatomyositis?

Answer 7

• Screen systematically for malignancy
• Prednisolone