JUVENILE DERMATOMYOSTITIS
DEFINITION:
A multiorgan rheumatologic disease characterized by acute and
chronic nonsupportive inflammation of striated muscle and skin.
EPIDEMIOLOGY:
- incidence: 1/200-280,000 (dermatomyositis/polymyositis)
- age of onset:
- mean - 7 years
- peak - 6 years (M) 6 and 10 years (F)
- risk factors:
- F > M (1.7:1) - immunogenetic predisposition:
- blacks > whites - HLA B8, DR3, C4q null allele
- familial (very rare) - immunodeficiencies
PATHOGENESIS:
- first described in 1887 by 4 different investigators
- in the Classification of Idiopathic Inflammatory Myositis,
JDM is Type IV
- currently viewed as a primary systemic vasculopathy rather
than an inflammation of muscle and skin as vasculitis and
noninflam-matory vasculopathy are hallmarks of JDM; thus the
etiological agent(s) produce blood vessel changes (endarteropathy,
capillaro-pathy, venopathy) which in turn lead to damage,
ulceration, in-farction, and destruction of the end organs
(striated muscle, skin, GI tract, and subcutaneous tissue)
- the primary lesion occurs in the endothelial cells which
contain reticulotubular inclusions that are the site of
thrombosis and vessel obliteration
2. Etiology
- unknown but two hypotheses:
- JDM after infection/immunization with rubella, BCG,
influenzae
- serological evidence of coxsackie B infection in early
JDM
- toxoplasma gondii, picornavirus, coxsackievirus,
paramyxovirus-like particles isolated in muscles
2. Autoimmune
- abnormality of T-cell immunity
- immune complex disease
- associated with immunodeficiencies
- hypogammaglobulinemia
- selective IgA deficiency
- C2 complement component deficiency
CLINICAL FEATURES:
- the classic presentation of acute proximal muscle weakness and
a characteristic skin rash (dermatitis) is pathognomonic of JDM
- anorexia
- fatique
- fever
- malaise
- weight loss
2. Musculoskeletal Manifestations (90-95%)
- limb girdle - proximal, symmetrical (Gower's sign)
- shoulder girdle, abdominal, anterior neck flexors, back
- pharyngeal, hypopharyngeal, palatal, respiratory muscles
- insidious (2/3) or acute (1/3); progressive
2. Muscle Pain
- stiff, edematous, indurated eventually becoming atrophic
and contractured
3. Cutaneous Manifestations (85-100%)
- usually occur a few weeks after onset of muscle symptoms
- in ¾'s, the dermatitis is pathognomonic for JDM
- Gottron papules - periungual & periarticular rash
(80-100%)
- subcutaneous & periorbital edema/erythema (60-90%)
- erythematous rash of malar area & V of chest (30-40%)
- photosensitive rash (5-40%)
- ulcerations (25%)
- heliotropic rash of eyelids (10-15%)
4. Other Manifestations
- Pulmonary disease - restrictive, fibrosis (80%)
- Gastrointestinal disease - acute mesenteric infarction
(10-60%)
- mucosal ulceration and pharyngitis (10-45%)
- Calcinosis - various types, healing process (20-40%)
- acute arthritis and arthralgia (7-38%)
- Raynaud's phenomenon (2-15%)
INVESTIGATIONS:
- elevation of skeletal muscle enzymes at onset (90-98%)
- tend to increase 5-6 weeks prior to onset and to decrease
3-4 weeks before improvement
- Enzyme (% of cases)
- AST (87%) - 20-40 x normal
- CK-MB (85%) - 20-40 x normal
- Aldolase A (65%)
- LDH (65%)
2. Electromyographic
- positive sharp waves, spontaneous fibrillations,
insertional activity
- findings represent membrane instability
3. Pathologic (Biopsy)
- vasculitis & non-inflammatory vasculopathy affect the
arterioles, capillaries, and venules
2. Striated Muscle
- BV changes + perifascicular myopathy with atrophy,
necrosis, fibre size variability (degeneration/regeneration),
inflammatory cell infiltrates
3. Skin
- BV changes + epidermal atrophy & hyperplasia, degeneration
of basal cells, inflammatory cell infiltrates
4. Gastrointestinal Tract
- BV changes + ulceration, infarction
4. Others
- calcinosis, muscle mass changes
2. Serum
- increased ESR & CRP (correlates with degree of
inflammation)
- ANA seropositive (variable)
- RF seronegative
- increased von Willebrand factor-related antigen
MANAGEMENT:
- respiratory (distress), gastrointestinal (bleeds, dysphagia),
skin (ulcers, photosensitivity, rash)
- usually no treatment necessary and may self-resolve
- with complications
- local wound measures
- surgical removal
- topical/systemic antibiotics
2. Physiotherapy
- goal is to prevent loss of range of motion and development
of contractures by passive range of motion exercises,
stretching, splinting, strengthening
3. Medications
- initial: 2 mg/kg/d bid for 1 month (max. 60 mg/kg/d)
- mainten: 1 mg/kg/d bid with a gradual taper over 2 years
to alternate day therapy
- should decrease serum striated muscle enzymes within 1-2
weeks
- should increase muscle strength within 1-2 months
- may not affect dermatitis
- SE: osteopenia, vertebral compression fractures, Cushing's
syndrome, growth retardation, steroid myopathy
2. Others
- Methotrexate
- ASA
- Axathioprine
- Cyclosporin
4. Prognosis
- good with early and vigorous control
- 40% mortality if untreated
- tends to become inactive after several years
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