The demonstration of muscle involvement using the MRI in four patients with dermatomyositis is reported from the Departments of Radiology and Pediatrics, University of Michigan Hospitals, Ann Arbor, MI. Ages ranged from 4½ to 18 years (median 8 years). The affected muscles had increased signal intensity on the T2 weighted images and normal appearance on the T1 weighted sequence. The mean intensity ratio for the patients with dermatomyositis differed significantly from that of four normal control children. Muscle groups with higher intensity ratios had lower scores on functional testing. Follow-up MRI scans demonstrated normal findings after treatment, coincident with progressive clinical improvement. 
COMMENT. The authors concluded that the MRI may be useful in the evaluation of dermatomyositis in children because it 1) is noninvasive, 2) has clear signal changes in affected muscle, 3) shows positive results at an early stage, 4) is a guide for biopsy, and 5) may assist in monitoring of the disease progress. The MRI appearances of muscles affected by hypotonic syndromes and muscular dystrophies differ from those of muscles affected by dermatomyositis. Ultrasound has been used in the diagnosis of patients with muscular dystrophy.