Proton magnetic resonance imaging and spectroscopic studies of the pathogenesis and treatment of juvenile dermatomyositis.

Juvenile dermatomyositis is an inflammatory disorder of muscle, skin, and connective tissue. Immune vasculopathy is central to the pathophysiology. We studied a 13-year-old boy with juvenile dermatomyositis using proton magnetic resonance imaging (MRI) with short tau inversion recovery (STIR), and proton magnetic resonance spectroscopy (MRS) to quantitate lipid and water in affected regions of muscle. Tissue perfusion was assessed by measuring tissue water concentration changes during isometric exercise of the tibialis anterior muscle. During sequential studies over 3 months of steroid treatment, STIR image abnormalities, resting water concentrations, and diminished perfusion returned to normal. Resting lipid concentrations increased during this period. MRI serves to guide muscle biopsy and monitor progress of the disease state. MRS demonstrates the vasculopathy and provides noninvasive assessment of steroid therapy in juvenile dermatomyositis.