Idiopathic inflammatory myopathies

Question 1

what is the typical presentation of idiopathic inlammatory myopathy?

Answer 1

Symmetrical diffuse proximal weakness (can’t get out of chair, brush hair, lifting objects and climbing steps)

+ skin manifestations (heliotrope rash, gouttron’s papules - eyelids, scaly plaques on joints, etc)

DISTAL MUSCLES SPARED SO FINE MOTOR FUNCTION IS CALM

CK, ESR and CRP raised – is associated with malignancy

Anti-jo-1 antibodies : polymyositis

Question 2

what do idiopathic inflammatory myopathy contain?

Answer 2

• polymyositis
• dermatomyositis

Question 3

define polymyositis and dermatomyostis?

Answer 3

Connective tissue diseases characterised by inflammation of muscles.

Characterised by insidious onset of progressive symmetrical proximal muscle weakness and autoimmune mediated striated muscle inflammation (myositis) associated with myalgia +/- arthralgia

Myalgia = muscle pain

Arthralgia = joint pain

Question 4

outline the aetiology/ risk factors for polymyositis and dermatomyositis?

Answer 4

Autoimmune basis

Viral infection has been implicated in its pathogenesis e.g. influenza, EBV

Dermatomyositis features myositis plus skin changes

Question 5

summarise the epidemiology of polymyositis and dermatomyositis?

Answer 5

RARE

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 FEMALES

Question 6

what are the presenting symptoms of polymyositis?

Answer 6

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

Dysphonia

Respiratory weakness –> SOB

NO rash

Question 7

what are the symptoms of dermatomyositis?

Answer 7

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 8

what are the signs of polymyositis?

Answer 8

Fever

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 9

what are the signs of dermatomyositis?

Answer 9

RASH characteristics

• Macular rash: shawl sign = rash over back and shoulders
• Lilac-purple heliotrope rash on eyelids often with oedema
• Nailfold erythema
• Gottron’s papules: roughened red papules over knuckles, elbows and knees

Rash may affect knees, shoulders, back and upper arms

Rash may be exacerbated by sunlight

Proximal myopathy

Muscle pain and tenderness in early disease

Fever

Question 10

what are the appropriate investigations for polymyositis?

Answer 10

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, ALT, AST, aldolase) - elevated

Question 11

what are the appropriate investigations for dermatomyositis?

Answer 11

Creatine kinase - not as reliable as in polymyositis

Enzymes (SGOT, SGPT and LDH, ALT, AST, aldolase 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