In vivo proton magnetic resonance spectroscopy in polymyositis and dermatomyositis: a preliminary study.

The aim of the study is to determine whether biochemical abnormalities, such as lipid, creatine and choline metabolites, are observed in the more distal muscles of polymyositis (PM) and dermatomyositis (DM) patients. 12 patients suffering from chronic active PM/DM and 9 controls underwent a combined proton magnetic resonance (MR) imaging and proton MR spectroscopy study of the calf muscle. From a combination of T1-weighted MR images and corresponding fat suppressed images, fat infiltration into the muscle of both PM and DM patients was consistently observed. Muscular atrophy with a variable distribution was also noted in all patients. The biochemical profile of the localised proton MR spectra of soleus muscle showed reduction of both 'choline' to lipid and 'creatine' to lipid ratios in chronic PM and DM patients when compared with controls.