Idiopathic Inflammatory Myopathies

Question 1

Define idiopathic inflammatory myopathies

Answer 1

Heterogeneous group of diseases characterised by muscle weakness and paraesthesia

Polymyositis – autoimmume: T-cell
mediated cytotoxic process

Dermatomyositis – autoimmune:
humoral attack against endothelium of
endomysial (muscle) blood vessels ->
capillary necrosis -> microinfarction and
inflammation -> perifasiscular atrophy

Question 2

What are the cuases/risk factors of idiopathic inflammatory myopathies?

Answer 2

Unknown aetiology
• HLA haplotypes
• Viruses e.g. coxsackie virus, HIV,
HTLV-1, influenza, EBV, CMV
• UV radiation
• Drugs e.g. statins, penicillamine

Overlap with connective tissue disorders
• Systemic lupus erythematosus
• Rheumatoid arthritis
• Mixed connective-tissue disease
• Sjögren’s syndrome
• Scleroderma

Question 3

What are the symptoms of idiopathic inflammatory myopathies?

Answer 3

• Fatigue
• Malaise
• Weight loss
• Insidious onset symmetrical proximal muscle weakness (esp. hip extensors)
• Difficulty with motor tasks e.g. rising from seat, climbing stairs, lifting/reaching
objects, combing hair
• Dysphagia
• Myalgia/arthralgia

Pulmonary involvement
• Interstitial lung disease
• Exertional dyspnoea

Cardiac involvement
• Heart failure
• Cardiomyopathy
• Pericarditis
• Arrhythmias
• Syncope
• Palpitations

Question 4

What are the signs of idiopathic inflammatory myopathies?

Answer 4

Polymyositis
• Muscle atrophy
• proximal myopathy

Dermatomyositis
• Heliotrope rash – violaceous discoloration and oedema of upper eyelids
• Gottron’s papules – erythema over knuckles and raised violaceous scalp eruption
• V-neck sign
• Shawl sign
• Skin calcinosis (in children)

Question 5

What investigations are carried out for idiopathic inflammatory myopathies?

Answer 5

• CK - elevated.
• EMG - diffuse spontaneous activity with fibrillation and positive sharp waves at rest.
• MRI - muscle oedema in acute myositis.
• Serology - Anti-Mi2
- Anti-Jo1
• Muscle Biopsy - mandatory for definitive diagnosis.
- In inclusion body myositis, inclusion bodies contain beta-amyloid that can be revealed by Congo red staining.
- Polymyositis: Endomysial inflammation
- Dermatomyositis: Petimysial inflammation