Metabolic disturbances during short exercises in dermatomyositis revealed by real-time functional 31P magnetic resonance spectroscopy.

OBJECTIVE (31)P magnetic resonance spectroscopy (MRS) is useful for evaluating metabolic disturbances in dermatomyositis (DM). However, short-term alterations of metabolic parameters such as Pi/PCr (inorganic phosphate/phosphocreatine) have not been assessed in detail, although they may reveal insights into the origin of the known long-term changes. We therefore performed real-time functional (31)P MRS to find out if there are characteristic short-term alterations of metabolic dynamics during muscular exercise and if they are of diagnostic relevance. METHODS MRS measurements were performed on lower calf muscles of 10 DM patients and 18 healthy subjects throughout five short (1 min) cycles of submaximal exercise (50% maximum voluntary contraction). RESULTS Pi/PCr ratios during exercise increased in patients and controls. They rapidly returned to baseline values in the controls, but both Pi and PCr remained above baseline values in patients and resulted in irregular Pi/PCr ratios. This was true for each individual patient, but resulted in broad variation in individual Pi/PCr values. To compare groups with limited patient numbers, it was therefore more appropriate to use a recovery index, i.e. the quotient of the Pi/PCr ratio during and after exercise, which was independent of individual parameters, such as age and the work/energy cost ratio. CONCLUSION Evaluation of short-term changes by real-time functional (31)P MRS provides insight into alterations of Pi/PCr ratios and could improve diagnostic parameters in DM.