MUSCLE ENERGY METABOLISM IN MULTIPLE SCLEROSIS MEASURED BY IN VIVO 31P MRS 476

Excessive fatigue defined as loss of function and lassitude is a common feature of multiple sclerosis (MS) patients. Our previous work employed in vivo 31PMRS to study muscle energy metabolism with respect to fatigue and paresis in MS patients using stimulated muscle exercise. In the present study we improved the technique with proton double resonance 31PMRS(31P{1H}). The purpose of this project was to evaluate changes in phosphocreatine (PCr) and pH in the flexor carpi radialis during and after voluntary grip exercise. PCr and pH were recorded constantly during a protocol including 1 min baseline, 3 min exercise and 5 min recovery. The generated force was assessed simultaneously and normalized to the maximum. The time when half of the maximum force was reached (T 1/2) was calculated. Subjects included 7 MS patients and 6 controls. Data were functionally categorized as follows: controls (group A); MS, normal arm function (group B); MS, arm weak but functional (group C); MS, arm weak, function compromised (group D). For group D, PCr and pH changed minimally in response to lack of exercise ability. Their force data indicated significantly lower force output and fast decline(T 1/2=4s) compared to all other groups (A=50s, B and C =30s). For group C the rate of PCr depletion and resynthesis was similar to group A, but delayed recovery of pH was observed. Maximal force in group C was slightly lower than group A and declined at a faster rate. The PCr and pH changes and force profile for group B were similar to group A, but the force dropped slightly faster. These results suggest that failure to activate motor pathways(as in group D) leads to significant deterioration of muscle function and metabolism. With partial activation and some paresis (group C), a degree of muscle fitness can be maintained with exercise and normal use. In the cases in which muscle activation is not compromised (group B), force and muscle metabolism appear normal. Thus, it appears that the degree of central activation compromise largely determines peripheral muscle characteristics.