Classical and amyopathic dermatomyositis seen at the National Skin Centre of Singapore: a 3-year retrospective review of their clinical characteristics and association with malignancy.

INTRODUCTION: Dermatomyositis is a condition well-known to medical physicians, especially rheumatologists and dermatologists. Classically, patients present with typical cutaneous features and proximal muscle weakness. Amyopathic dermatomyositis has been reported in recent literature where patients present with skin changes without muscle involvement.
MATERIALS AND METHODS: We reviewed 28 patients diagnosed with dermatomyositis at the National Skin Centre over a 3-year period from 1996 to 1998 to assess the prevalence of this amyopathic variant in our local population and its association with malignancy.
RESULTS: Out of the 28 patients, 13 (46.4%) had no clinical or laboratory evidence of myositis at presentation. Nine patients (32.1%) had clinical muscle weakness and 6 patients (21.4%) had laboratory evidence of myositis. Malignancies were detected in 12 patients (42.8%), half of which were nasopharyngeal carcinomas. There was no significant difference in the prevalence of malignancy between those with detectable muscle weakness (33.3%) and those without (47.4%). However, there was a significant higher prevalence of malignancy in those with clinical and laboratory evidence of myositis (66.6%) than those without (15.4%).
CONCLUSION: We conclude that amyopathic dermatomyositis is a common presentation in our population and may have a lower risk of malignancy than the classical variant. Screening for malignancy, especially nasopharyngeal carcinoma, is recommended for all dermatomyositis patients.