Serial magnetic resonance imaging in juvenile dermatomyositis--delayed normalization.

Demonstration of myositis in juvenile dermatomyositis (JDM) has traditionally required the presence of two out of three objective findings including muscle enzyme studies, electromyography, and muscle biopsy. Magnetic resonance imaging (MRI) is considered another objective criterion and has been recommended for follow-up studies as well. We report on a 6-year-old girl with JDM, presenting with facial rash and proximal muscle weakness, in whom MRI, in conjunction with elevated creatinine kinase (CK) levels, was diagnostic, with an increased T2 signal of proximal muscles. MRI reflected exacerbation of myositis in spite of steroid therapy 2 weeks later, but failed to mirror normalization of muscle strength and CK values 10 weeks later. In fact, improvement of MRI followed clinical and laboratory normalization with a delay of 2 months. This possible delay should be considered when MRI is used to monitor the response to therapy.