Dermatomyositis: correlative MR imaging and P-31 MR spectroscopy for quantitative characterization of inflammatory disease.

Magnetic resonance (MR) imaging and phosphorus-31 MR spectroscopy were used to examine four patients with dermatomyositis and five control subjects. T2-weighted images of the thigh muscles of patients showed increased signal intensity, with focal and inhomogeneous involvement predominantly in the vastus lateralis and secondarily in the vastus intermedius and vastus medialis. T1 and T2 values of the vastus lateralis in patients were significantly higher than those of the control subjects. T1 values of the rectus femoris and biceps femoris with more generalized inflammation were moderately elevated but still significantly higher than those of the control subjects. P-31 MR spectra of the quadriceps muscles were obtained during rest, during exercise at two graded levels, and in recovery. Concentrations of adenosine triphosphate and phosphocreatine (PCr) in the diseased muscles were 30% below normal values, and the inorganic phosphate/PCr ratios were increased in the patients' muscles at rest and throughout exercise. The T1 and T2 values as well as the P-31 metabolite data correlated with symptoms and clinical assessment.