JUVENILE DERMATQMYQSiTiS

Juvenile dermatomyositis (JDM) is the commonest inflammatory myopathy in childhood, characterized by typical rash and symmetrical proximal myopathy.

Etiology is idiopathic, probably an autoimmune disorder with inherent genetic susceptibility, triggered by preceding intestinal or respiratory infections.

Pathologically, it is characterized by an underlying vasculopathy with immune complex and complement deposition, leading to vascular occlusions and infarcts, inflammatory cell infiltration and extensive fibrosis in skin and muscles.

Clinically, it is more common in females with peak age of onset between 8 and 12 years, which is usually insidious with vague constitutional complaints, followed by:

• Characteristic violaceous rash over upper eyelids (Heliotrope eyelids), with or without periorbital puffiness and telangiectasia. Other skin lesions include similar rash on other sun-exposed parts and hypertrophic pale red papules over metacarpal or proximal interphalangeal joints, i.e. Gottron papules (Fig. 24.3).

• Slowly progressive symmetrical muscular weakness after 2-3 months of rash, presenting with functional

Fig. 24.3A and B: Juvenile dermatomyositis: (A) Heliotrope eyelids; (B) Gottron papules.

(Courtesy: Dr Raju Khubchandani)

TABLE 24.8: Diagnostic criteria for dermatomyositis

• Typical rash (Heliotrope eyelids, Gottron papules) and

• Any three of following features

- Symmetrical proximal muscle weakness

- Elevated muscle enzymes (CPK, LDH)

- Typical EMG findings*

- Muscle biopsy suggestive of chronic inflammation *Fasciculations, irritability and high-frequency discharges

impairment, e.g.

• Complications may result due to muscular weakness or diffuse vasculopathy and include—(a) recurrent aspiration, interstitial pneumonia or fibrosing alveolitis, (b) intestinal perforation or bleeding, (c) seizures, (d) retinitis, (e) mucosal ulcerations, and (f) calcinosis, i.e. calcium deposits in muscles and subcutaneous tissues in late stages.

Diagnosis depends on essential presence of typical rash with any three of the clinical or laboratory evidence of muscular injury (Table 24.8). Presence of only two of these evidences (instead of 3) with rash is considered as a probable case.

MRI helps to identify exact site of active disease for biopsy and EMG studies, as well as to make an early diagnosis before appearance of muscle enzyme abnor­malities. ESR is usually normal and ANA is present in gt;80% cases. Soft-tissue calcinosis may be seen on X-rays and pulmonary function tests may reveal restrictive lung disease.

D/D includes other rheumatoid disorders with rash, e.g. SLE or other causes of myopathy, e.g., vial myositis, metabolic myopathies, etc.

Treatment revolves around steroid therapy (PO pre­dnisolone 2 mg/kg/day) till normalization of muscle enzymes and clinical recovery, followed by low-dose alter- nate-day therapy for minimum 2 years. In severe cases,

IV methylprednisolone may be used in initial stages, followed by oral prednisolone maintenance. PO/IV/SC Methotrexate (15 mg/m²/day) may be used as steroid- sparing agent along with folic acid supplements.

Hydroxychloroquine (PO 3-5 mg/kg/day) is used as a second-line disease modifying agent. In steroid-resistant/ dependent cases, other drugs, e.g. cyclophosphamide, cyclosporine, rituximab or IV immunoglobulins may be considered.

Supportive therapy includes use of sunscreens to prevent rashes, nasogastric feeding in dysphagia, and ventilatory support for respiratory paralysis. Physical and occupational therapy with muscle stretching exercises should begin as soon as acute inflammation subsides.

Prognosis has markedly improved with aggressive immunosuppressive therapy, though acute phase may last for 12-18 months and recovery is better in children than in adults. Overall mortality is lt;5%, though long­term disabilities are common even in treated cases.

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