Juvenile clinically amyopathic dermatomyositis (CADM): Case-based review

Background

Clinically amyopathic dermatomyositis (CADM) is rare as the classical cutaneous features are present with absence of myopathy and the serum creatinine kinase, electromyographic examination and muscle biopsy are usually normal.

Aim of the work

To report a young girl with juvenile CADM who responded to corticosteroid and mycophenolate mofetil, without progressing to myopathy and other systemic complications over a 3-year period.

Case presentation

An 11-year-old Malay girl was afebrile and presented with debilitating polyarthritis and classical cutaneous manifestations of dermatomyositis which was confirmed by histological findings, but without myopathy and systemic involvement. The anti-nuclear antibody (ANA) was positive 1:160, with speckled pattern and anti-p155/140 antibodies (anti-transcriptional intermediary factor 1, anti-TIF1γ antibody) were positive. Skin biopsy revealed typical histological findings consistent with dermatomyositis including vacuolar changes of the basal layer, increased lymphocytic infiltrate and increased mucin deposition in the dermis. She received pulse methylprednisolone (250 mg/day/3 days) followed by oral prednisolone 1 mg/kg/day tapered until her cutaneous lesions showed marked improvement. Hydroxychloroquine (HCQ) (200 mg/day) and oral methotrexate (10 mg/week) were added. Six months after initial treatment, mycophenolate mofetil (MMF) 1 g/day was added in view of the slow improvement of her cutaneous lesions and was discontinued a year later as she demonstrated favourable outcome. Besides the skin lesions, her arthritis also responded well to treatment.

Conclusion

Juvenile CADM is rare but with early recognition and treatment, the prognosis is good especially in children as this may reduce the risk of systemic complications and progression to myopathy.