Dermatomyositis with normal muscle enzyme concentrations. A single-blind study of the diagnostic value of magnetic resonance imaging and ultrasound.
BACKGROUND AND METHODS: It is well documented that the cutaneous lesions of dermatomyositis may precede clinical myositis or may occur in the absence of any muscle disease detectable by current diagnostic criteria. In this single-blind study, we used magnetic resonance imaging (MRI) and ultrasound to evaluate five patients who presented with classical clinicopathologic dermatomyositis, but with normal levels of serum muscle enzymes. This patients group has not been previously studied with these techniques. Patients who served as positive and negative control subjects were also examined. RESULTS: Ultrasonography revealed hyperechogenicity, and MRI revealed high signals on T2-weighted images in several muscle groups of the patient with active myositis (positive control). Increased echogenicity was also noted in the deltoid region of one patient who had previously had a normal muscle biopsy finding. In the same patient, MRI revealed inflammatory changes in the lumbar paraspinal muscles. Another patient, with all previous study results being normal, had MRI evidence of T2 high signals in the gluteus minimus. CONCLUSIONS: Noninvasive examinations such as MRI and ultrasound are beneficial as adjunctive means of examination in the evaluation of patients with dermatomyositis sine myositis or dermatomyositis. Future studies may suggest additional uses for these tests, including serial evaluation of patients, noninvasive confirmation of diagnosis in pediatric patients, or in directing muscle biopsy, thus increasing sensitivity. Ultrasound appears to be the more cost-effective and simple test; but MRI, although more expensive, may be more sensitive and specific.