Chapter 29: Rheumatology

DERMATOMYOSITIS/JUVENILE DERMATOMYOSITIS (JDM)

Most common pediatric inflammatory myopathy; Bohan and Peter diagnostic criteria (definite JDM: heliotrope rash or Gottron papules plus at least three criteria; probable JDM: heliotrope rash or Gottron papules plus two criteria)

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

• Progressive symmetric proximal muscle weakness

• Elevated skeletal muscle enzymes (creatine phosphokinase, aspartate aminotransferase [AST], aldolase, lactate dehydrogenase [LDH])

• Electromyogram (EMG) consistent with myopathy

• Biopsy evidence of myositis

• Updated criteria will likely include muscle abnormalities on MRI short T1 inversion recovery (STIR) or T2 sequence

Epidemiology

• Incidence: About 2–3 cases in 1 million children

• Peaks at 4 to 9 years of age

• Girls > boys (2:1)

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

Etiology

• Potential infectious triggers: Group A beta-hemolytic Streptococcus, coxsackievirus B, parvovirus, Epstein–Barr virus (EBV), others

• HLA and tumor necrosis factor α (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) and has a higher age at onset and a more severe disease presentation, includes proximal and distal weakness and muscle atrophy, and lacks skin abnormalities; calcinosis is rare.

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

  • ✓ Systemic Sclerosis

  • ✓ Juvenile idiopathic arthritis; polyarticular or systemic

  • ✓ Polyarteritis nodosa

  • ✓ Eosinophilic fasciitis

• Infectious

  • ✓ Viral myopathies: Influenza, coxsackievirus, echovirus, parvovirus, EBV, herpes simplex virus, parainfluenza virus, adenovirus, enterovirus

  • ✓ Bacterial and parasitic myopathies: Staphylococcus, Streptococcus, Toxoplasma, Trichinella

• 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

• Autoimmune angiopathy

• Perivascular inflammation, mostly mononuclear cells

• Swelling and blockage of capillaries, tissue infarction, perifascicular 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 (with involvement of nasolabial folds in contrast to SLE); papulosquamous eruption on extensor surfaces (Gottron rash), particularly over interphalangeal joints; shawl sign (erythematous rash in a shawl distribution); cutaneous calcinosis and ulceration

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

• Arthritis: Can be transient or persistent, with or without tenosynovitis, flexor nodules; flexion contractures due to myofascial inflammation

• Mucocutaneous: Oral ulcers, gingival inflammation

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

• Gastrointestinal (GI): Dysphagia, enteric ulceration with or without perforation, bleeding, constipation, diarrhea, abdominal pain

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

• Other ...