Dermatomyositis sine myositis in five cases

Background A small subset of patients with dermatomyositis develop the characteristic cutaneous manifestations without muscle involvement, the so-called dermatomyositis sine myositis or amyopathic dermatomyositis. Whether systemic treatment of skin disease can prevent the development of myositis remains controversial. Objective The purpose of this study was to evaluate the development of the disease in terms of the onset of muscle symptoms under systemic treatment with corticosteroids or antimalarials. Methods Five patients with dermatomyositis sine myositis were included in this study. All skin biopsy specimens had features consistent with dermatomyositis. Muscle enzymes, electromyograms and muscle biopsies did not reveal any abnormality. Results Corticosteroids were given in three patients and hydroxychloroquine in two. Both regimens proved to be effective in the treatment of skin symptoms. Four patients, three on corticosteroids and one on hydroxychloroquine, did not develop muscle disease 4–7 years after presentation. One patient on hydroxychloroquine showed laboratory evidence of myositis 6 years after initiation of treatment. Conclusion It seems that muscle disease may appear within long periods of time after the onset of the cutaneous manifestations. The term dermatomyositis sine myositis can be used as a provisional diagnosis. Our observations suggest that systemic treatment of skin disease with corticosteroids is successful and may alter the disease course. Hydroxychloroquine may be helpful in some cases.