Mitochondrial encephalomyopathy: correlation of P-31 exercise MR spectroscopy with clinical findings

To evaluate the sensitivity of standardized exercise phosphorus-31 magnetic resonance (MR) spectroscopy in screening for subclinical muscle involvement in mitochondrial encephalomyopathy and to estimate if changes seen at biopsy have functional consequences.

Exercise MR spectroscopy was performed in 52 examinations of 18 healthy volunteers and 14 patients with defects of mitochondrial respiratory chain enzymes. Calculation and kinetic analysis of the phosphocreatine (PCr) index and pH time courses were standardized with a microcomputer program.

PCr index scores and conventional test scores matched in 10 of 14 cases. No obvious correlation existed between pH parameters and clinical score. Muscle affection, according to pH parameter score, was rated moderate (n = 3), severe (n = 1), or maximum (n = 2) in six of 14 cases in which clinical test scores showed only mild affection.

Exercise MR spectroscopic PCr index parameters provide diagnostic information on skeletal muscle involvement in patients with mitochondrial encephalopathy. The sensitivity of the PCr index parameter seems equal or superior to that of conventional diagnostic tests. The role of pH parameters, however, has yet to be defined.