MR Imaging in Amyopathic Dermatomyositis

Purpose: Amyopathic dermatomyositis is a distinct clinical entity with cutaneous involvement but no myopathy. We conducted a prospective study to investigate the role of MR imaging in these patients.

Material and Methods: Out of 40 Chinese patients presenting with dermatomyositis, based on clinical assessment and normal serum muscle enzymes 10 were diagnosed as having amyopathic dermatomyositis. These 10 patients underwent MR imaging for evaluation of any subclinical muscle involvement.

Results: Three patients demonstrated abnormal signal intensity in muscles on both T2- and fat suppression sequences. Thus, one-third of patients with dermatomyositis and clinically normal muscles may have detectable muscle inflammation on MR images, indicating that MR has a potential role for locating the relevant biopsy site and for longitudinal follow up. Six of the 10 patients had malignant disease diagnosed before or after diagnosis of the cutaneous manifestation. Nasopharyngeal carcinoma was the most common malignant disease in this group of patients.

Conclusion: MR imaging is recommended for demonstrating subclinical muscle involvement in patients with the clinical diagnosis of amyopathic dermatomyositis. We also recommend screening for malignancy, particularly nasopharyngeal carcinoma, in Southern Chinese patients with dermatomyositis.