+++
DERMATOMYOSITIS/JUVENILE DERMATOMYOSITIS (JDM)
++
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
++
-
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
++
-
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:
-
Other:
++
-
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 ...