Idiopathic inflammatory myopathies

Question 1

Define polymyositis and dermatomyositis

Answer 1

Inflammatory myopathies = idiopathic primary inflammatory myopathies characterised by chronic inflammation of striated muscle (polymyositis) with occasional skin involvement (dermatomyositis)

Question 2

Explain the aetiology/risk factors of polymyositis and dermatomyositis

Answer 2

Autoimmune basis

Viral infection has been implicated in its pathogenesis

Question 3

Summarise the epidemiology of polymyositis and dermatomyositis

Answer 3

Polymyositis presents between 30-60 yrs

Dermatomyositis can occur at any age (peak onset: 5-10 (children) and 50 (adults))

Both diseases are 2 x more common in FEMALE

Question 4

Recognise the presenting symptoms of polymyositis

Answer 4

Inflammatory myopathy with onset over weeks or months

Steady progression of symptoms

Diffuse weakness in proximal muscles

Causing difficulty rising from a low chair, climbing steps, lifting objects and combing hair

Also fatigue, myalgia and muscle cramps

Distal muscles are spared - so fine motor coordination tends to be preserved in the early stages

Pharyngeal weakness –> dysphagia

NO rash

Question 5

Recognise the presenting symptoms of dermatomyositis

Answer 5

Inflammatory myopathy with onset over weeks or months

RASH

Systemic upset with fever, arthralgia, malaise and weight loss

Possible cardiac disease (e.g. conduction blocks, tachyarrhythmia)

GI ulcers and infections

Interstitial lung disease (30-50%)

Children have more non-muscular features (e.g. GI ulcers and infections)

Question 6

Recognise the signs of polymyositis on physical examination

Answer 6

Muscle weakness

NOT painful in most patients

Proximal myopathy

Extraocular muscles and distal muscles are spared

Weak forced flexion of the neck

Muscular atrophy

Muscles may be tender on palpation

Question 7

Recognise the signs of dermatomyositis on physical examination

Answer 7

RASH characteristics

Blue-purple discolouration of the upper eyelids with periorbital oedema

Flat red rash involving the face and upper trunk

Raised purple-red scaly patches over the extensor surfaces of joints and finger

Rash may affect knees, shoulders, back and upper arms

Rash may be exacerbated by sunlight

Proximal myopathy

Muscle pain and tenderness in early disease

Question 8

Identify appropriate investigations for polymyositis

Answer 8

Creatine kinase - up to 50 x higher than normal

Electromyography (EMG)

Muscle biopsy-DEFINITIVE TEST

Autoantibodies (e.g. myositis specific antibody, anti-Jo-1 antibody)

Enzymes (e.g. SGOT, SGPT, LDH)

Question 9

Identify appropriate investigations for dermatomyositis

Answer 9

Creatine kinase - not as reliable as in polymyositis

Enzymes (SGOT, SGPT and LDH may be raised)

Autoantibodies
ANA
Anti-Mi-2
Anti-Jo-1 (more common in polymyositis)

EMG - may be helpful but can be normal as well

Muscle biopsy