Idiopathic inflammatory myopathies (incl. polymyositis, dermatomyositis)

Question 1

What imaging may be used to confirm the diagnosis of dermatomyositis?

Answer 1

MRI of affected muscles, EMG, muscle biopsy.

Question 2

What condition is dermatomyositis/polymyositis associated with in adults?

Answer 2

Malignancy - so always investigate especially in dermatomyositis.

Commonly a paraneoplastic syndrome from these cancers:

• Lung
• Pancreatic
• Ovarian
• Bowel

Question 3

Which antibodies are found in dermatomyositis/polymyositis?

Answer 3

• Anti-Jo1
• Anti-Mi2
• ANA positive in 80%

Question 4

Define dermatomyositis/polymyositis.

Answer 4

Rare conditions with insidious onset of progressive symmetrical proximal muscle weakness and AI-mediated striated muscle inflammation associated with myalgia +/- arthralgia.

Question 5

What is the epidemiology of dermatomyositis?

Answer 5

• Bimodal - 5-15yrs and 40-60yrs
• F>M
  *

Question 6

What are the clinical features of dermatomyositis and polymyositis?

Answer 6

• Myalgia +/- arthralgia - symmetrical proximal
• Dysphagia
• Dysphonia (poor phonation)
• Dermatomyositis
  
  • Macular rash (shawl sign +ve if over back and shoulders)
  • Lilac-purple heliotrope rash on eyelids +/- oedema
  • Nailfold erythema (dilated capillary loops)
  • Gottron’s papules on knuckles, elbows, knees
• Fever
• Raynaud’s
• ILD fibrosis
• Myocarditis, arrhythmias

Question 7

What investigations are used to diagnose dermatomyositis/polymyositis?

Answer 7

• Muscle enzymes (ALT, AST, LDH, CK and aldolase) - raised
• EMG - shows characteristic fibrillation potentials
• Muscle biopsy - confirms diagnosis and excludes other conditions
• MRI - muscle oedema in acute myositis
• Autoantibodies - anti-Mi2 and anti-Jo

Question 8

What is found on muscle biopsy in dermatomyositis/polymyositis?

Answer 8

Perivascular or inter-fascicilar inflammation

Question 9

What prognostic information does presence of autoantibodies in dermato/polymyositis give?

Answer 9

Anti-Mi2 and anti-Jo1 are associaed with interstitial lung disease and acute onset so must be treated quickly

Question 10

What are the differentials in inflammatory myopathies?

Answer 10

• Carcinomatous myopathy
• Inclusion-body myositis
• Muscular dystrophy
• PMR
• Endocrine/metabolic myopathy e.g steroids
• Rhabdomyolysis
• Infection e.g. HIV
• Drugs e.g. penicillamine, colchicine, statins, chloroquine

Question 11

What is the management of dermatomyositis/polymyositis?

Answer 11

• Photoprotection
• Prednisolone - high dose for 2-4 weeks. IV for acute severe flares for 3-5days.
  
  • +/- IVIG - sometimes preferred over steroids
• Immunosuppression and cytotoxics - used early in resistant disease. Options:
  
  • Methotrexate once weekly
  • Azathioprine OD
  • MMF BD
  • Ciclosporin
  • Cyclophosphamide
  • Tacrolimus
• Ritiximab
• Hydrocortisone, hydroxychloroquine/topical tacrolimus - for skin disease

Question 12

What is the prognosis for dermatomyositis/polymyositis?

Answer 12

1 in 3 will experience permanent disability which can be severe

Treatment is usually lifelong