Inflammatory myopathies

Question 1

Define

Answer 1

Idiopathic primary inflammatory myopathies characterized by chronic inflammation of striated muscle (polymyositis and inclusion body myositis, IBM) and skin (dermatomyositis)

Question 2

Causes

Answer 2

aetiology unknown
?infective or malignant trigger in genetically predisposed individ

Question 3

Risk factors

Answer 3

 Polymyositis may be associated with autoimmune connective tissue diseases (e.g. scleroderma)

 Dermatomyositis may be associated with bronchial, stomach, testicular, breast and ovarian malignancy – and auto-antibodies anti-Jo-1, anti-Scl, anti-Mi2, HLA linkage to DRW52

Question 4

Epidemiology

Answer 4

RARE, annually 0.2–1/100 000
Peaks at childhood (5–15 years) and adult (40–60 years) More common in women

Question 5

Symptoms

Answer 5

General → fatigue, malaise, dyspnoea±Myalgia and arthralgia

Polymyositis and dermatomyositis → gradual onset (3-6 months) of progressive painless proximal muscle weakness
(E.g. difficulty raising arms above head, rising from chair, climbing stairs)

Distal muscles are spared so fine movements of the hand are affected in only very late stages

Inclusion body myositis → insidious onset (months-years)Affects dexterity of hands, ±dysphagia and neck droop, foot drop

Question 6

Signs

Answer 6

Polymyositis and dermatomyositis → proximal muscle weakness and atrophy affecting both upper and lower limbs
Muscles may be tender on palpation and may have a nodular grainy feel

Muscular atrophy occurs with preservation of tendon reflexes, flexor plantar response and normal sensation

Inclusion body myositis → proximal and distal muscle weakness and atrophy (particularly wrist/finger flexors, quads)
Weakness of erector spinae and dysphagia
↓Deep tendon reflexes

Skin lesion in dermatomyositis

•  Macular ‘lilac’ heliotrope rash on upper eyelids with
• periorbital oedema
•  Rash on chest wall, neck, elbows or knees
•  Gottren’s papules (scaly erythematous raised plaques on
• finger joints, periungal telangiectasia, ragged cuticles)
•  Mechanics hands (fissuring dermatitis of finger pads)