Table 1

Classical clinical features of idiopathic inflammatory myopathies

DiseaseDemographic featuresClinical key featuresAutoantibodies and possible additional features
DermatomyositisAll ages.
Peak incidence ages 40–60 years and 5–14 years.
Female predominance.
Symmetrical weakness.
Proximal > distal weakness.
Neck flexor > neck extensor weakness.
Dysphagia.
Subacute onset.
Classic dermatomyositis rash.
MDA5
  • Amyopathic/pauci-myopathic.

  • Rapidly progressive severe interstitial lung disease.

  • Classic and atypical dermatomyositis rash, mechanic’s hands, palmar papules, digital ulcers, panniculitis.

  • Polyarthritis.

NXP2
  • Cancer (adults).

  • Severe weakness.

  • Calcinosis.

  • Children: vascular involvement.

Mi2
  • Severe weakness and high serum creatine kinase.

  • Classic dermatomyositis rash in light-exposed areas.

TIF1-γ
  • Cancer (adults).

  • Pauci-myopathic.

  • Dysphagia.

  • Classic dermatomyositis rash.

  • Children: skin involvement, chronic disease course.

SAE1
  • Cancer (Asia).

  • Amyopathic at onset—skin symptoms precede weakness.

  • Dysphagia.

  • Interstitial lung disease (Asia).

Antisynthetase and related syndromesAdolescents/Adults.Symmetric weakness.
Proximal > distal weakness.
Neck flexor > neck extensor weakness.
Dysphagia.
Antisynthetase syndrome:
  • Subacute onset.

  • Mechanic’s hands/skin lesions.

  • Fever.

  • Raynaud’s phenomenon.

  • Arthritis.

  • Cardiac involvement.

Jo1
  • Cancer (Asia).

  • Severe weakness.

  • Arthritis.

  • Early treatment with rituximab.

PL7
  • Mild weakness.

  • Severe interstitial lung disease.

  • Arthritis.

PL12
  • Cancer (Asia).

  • Mild weakness.

  • Severe interstitial lung disease.

OJ
  • Severe weakness.

  • Severe interstitial lung disease.

KS
  • Severe interstitial lung disease.

ZO
  • Antisynthetase syndrome.

EJ
  • Antisynthetase syndrome.

Tyrosyl
  • Antisynthetase syndrome.

Non-specific myositisAdolescents/Adults.Symmetric weakness.
Proximal > distal weakness.
Neck flexor > neck extensor weakness.
Dysphagia.
Subacute onset.
Association with systemic disease.
PM-Scl (75/100)
  • Associated with scleroderma and systemic lupus erythematosus.

  • Remission rare.

  • Cardiac comorbidity.

  • Interstitial lung disease.

RNP
  • Associated with mixed connective tissue disease.

Ku
  • Associated with systemic sclerosis, systemic lupus erythematosus, Sjögren’s syndrome.

  • Therapy-resistant interstitial lung disease.

SSA (Ro52, Ro60) and SSB (La)
  • Associated with systemic sclerosis, systemic lupus erythematosus, Sjögren’s syndrome, antisynthetase syndrome, rheumatoid arthritis.

Immune-mediated necrotising myopathyAll ages.
Female predominance.
Severe symmetric limb weakness.
Axial weakness.
Muscle atrophy.
Dysphagia.
Very high serum creatine kinase (>10× upper limit of normal).
Subacute onset.
HMGCR
  • Cancer (adults).

  • Statin exposure.

  • Intravenous immunoglobulins are preferred over rituximab.

SRP
  • Severe weakness.

  • Treatment resistance.

  • Children: cardiac disease, arthritis; early treatment sometimes favourable outcome.

  • Early treatment with rituximab or intravenous immunoglobulins.

‘seronegative’
  • Interstitial lung disease.

  • Cancer (adults).

  • Cardiac involvement.

Inclusion body myositis>45 years.
Male predominance.
Co-occurrence with autoimmune disease in one-third.
(A)symmetric weakness.
Selective involvement of quadriceps and deep finger flexors.
Dysphagia.
Facial/axial weakness.
Insidious onset.
cN-1A
  • Bulbar weakness.

  • Higher mortality.

  • Less proximal arm weakness.