USE OF MAGNETIC-RESONANCE-IMAGING AND P-31 MAGNETIC-RESONANCE SPECTROSCOPY TO DETECT AND QUANTIFY MUSCLE DYSFUNCTION IN THE AMYOPATHIC AND MYOPATHIC VARIANTS OF DERMATOMYOSITIS

Objective. To investigate the use of magnetic resonance imaging (MRI) and P-31 magnetic resonance spectroscopy (MRS) in characterizing the m etabolic and functional status of muscles in patients with amyopathic dermatomyositis (DM) and to compare the findings with those in patient s with classic myopathic DM. Methods. Nine patients with amyopathic DM , 11 patients with myopathic DM, and 11 normal individuals were studie d. MRI images of thigh muscles were obtained, and T1 and T2 relaxation times were calculated. Biochemical status was quantitated with P-31 M RS, by determining concentrations of phosphate metabolites during rest and exercise. Results. Patients with amyopathic DM showed no muscle i nflammation, and MRS data obtained during rest were normal, During exe rcise at 25% and 50% maximum voluntary contractile force, the MRS data revealed significant differences between amyopathic DM patients and c ontrol subjects indicating inefficient metabolism, In contrast, muscle s of patients with myopathic DM showed inflammation and metabolic abno rmalities even during rest. Conclusion. Metabolic deficiencies in pati ents with amyopathic DM were unmasked by exercise, suggesting that the 2 DM syndromes may share muscle abnormalities, MRI/MRS may be useful in diagnosis and optimization of treatment,