CHAPTER 28: Rheumatology

DERMATOMYOSITIS/JUVENILE DERMATOMYOSITIS (JDM)

DEFINITION

Most common pediatric inflammatory myopathy.

Bohan and Peter diagnostic criteria (definite JDM: heliotrope rash or Gottron’s papules plus at least three criteria; probable JDM: heliotrope rash or Gottron’s papules plus two criteria)

• Heliotrope rash (eyelids) or Gottron’s papules (extensor surfaces)

• Progressive symmetric proximal muscle weakness

• Elevated skeletal muscle enzymes (CK, AST, aldolase, LDH)

• EMG consistent with myopathy

• Biopsy evidence of myositis

• Updated criteria will likely include muscle abnormalities on MRI STIR or T2 sequence

EPIDEMIOLOGY

• Incidence: About 2–3 cases/million children

• Peaks at 6 years and 11–12 years of age; female:male is 2:1

• Comparable for blacks and whites, lower in Hispanics

• Unlike in adults, JDM has no definite associations with malignancy

ETIOLOGY

• Potential infectious triggers: Group A beta-hemolytic Streptococcus, coxsackie virus B, parvovirus, others

• HLA and TNF-α alleles may predispose a child to JDM

• Molecular mimicry is suspected

• Sun exposure may trigger onset of rash

DIFFERENTIAL DIAGNOSIS

• Rheumatologic:

  • ✓ Juvenile polymyositis is rare in children (2–8% of inflammatory myopathies), has similar age and sex distribution as JDM but includes proximal and distal weakness, muscle atrophy, lacks skin abnormalities, and calcinosis is rare

  • ✓ Systemic lupus erythematosus (SLE) and related conditions (e.g., mixed connective tissue disease, Sjögren syndrome)

  • ✓ Scleroderma

  • ✓ Juvenile idiopathic arthritis (JIA); polyarticular or systemic

  • ✓ Polyarteritis nodosa

  • ✓ Eosinophilic fasciitis

• Infectious:

  • ✓ Viral myopathies: Influenza A and B, coxsackie, Epstein–Barr virus, herpes, parainfluenza, adenovirus, enterovirus

  • ✓ Bacterial and parasitic myopathies: Staph, strep, toxoplasma

• Metabolic/Genetic:

  • ✓ Muscular dystrophies

  • ✓ Congenital myopathies

  • ✓ Myotonic disorders

  • ✓ Glycogen storage diseases

  • ✓ Periodic paralysis

  • ✓ Endocrinopathies

• Other:

  • ✓ Trauma

  • ✓ Toxins

  • ✓ Drug-induced myopathies

  • ✓ Disorders of neuromuscular transmission

PATHOPHYSIOLOGY

• Perivascular inflammation, mostly mononuclear cells

• Swelling and blockage of capillaries, tissue infarction, perifasicular atrophy

• Chronic inflammation ensues with fibrosis and microscopic calcification

CLINICAL MANIFESTATIONS

• Proximal muscle weakness (neck flexors, shoulders, abdomen, thighs): Gower sign, difficulty climbing stairs or combing hair

• Skin: Heliotrope rash (violaceous rash of eyelids); facial erythema, possibly in malar distribution; papulosquamous eruption on extensor surfaces (Gottron’s rash), particularly over interphalangeal joints (Gottron’s papules); shawl sign (erythematous rash in a shawl distribution); cutaneous calcinosis and ulceration

• Nailfolds: Capillary drop-out, capillary dilation, cuticular hypertrophy

• Arthritis: Effusions, limited range of motion, pain, deformity

• Mucocutaneous: Oral ulcers, gingival inflammation

• Pulmonary: Shortness of breath, cough, crackles can be consistent with interstitial lung disease or aspiration pneumonia

• Gastrointestinal: Dysphagia, ulceration, perforation, bleeding, constipation, diarrhea, abdominal pain

• Other manifestations: Lipodystrophy, polyneuropathies, retinal exudates, and cotton wool patches

• Other complications: Calcinotic lesions may spontaneously drain causing local inflammatory response and superinfection; can form exoskeleton; vasculitic ulcers; rare arrhythmias and cardiomyopathy; complications of chronic corticosteroid exposure (growth failure, hypertension, vertebral compression fractures, striae, avascular necrosis, cataracts, glaucoma)

DIAGNOSTICS