Correlation between symptom fatigue and muscular fatigue in multiple sclerosis

The symptom of fatigue is a frequent complaint in multiple sclerosis (MS) patients. Signs of fatigability have been documented in these patients as well. However, correlation with signs of objective fatigue had not been clarified in MS. The aim of this study was to ascertain the existence of muscular fatigue in multiple sclerosis patients, and to find out if there is a correlation between the subjective symptom of fatigue and muscular fatigue. Fifty MS patients and 50 age and sex matched volunteers were studied using isometric and isotonic tests using the dominant hand. Strength was studied in the baseline condition and also after recovery of either an isotonic (experiment A) or isometric effort (experiment B), Maximum strength, strength in relationship to weight, slope of fatigability in 11 consecutive contractions, and strength and duration of a maximum effort were calculated. Fatigue as a symptom was measured using the Fatigue Severity Scale (FSS) and the Fatigue Descriptive Scale (FDS). Non-parametric techniques were used for the statistical analysis. Patients with MS had less isometric and isotonic strength, but the recovery was the same as recovery in the control group. There was a negative linear correlation between the symptom of fatigue and the baseline strength. In conclusion, this study supports the existence of signs of muscular fatigue in MS patients. However, the recovery after exercise is normal. The correlation between the baseline scores in strength and the symptom of fatigue suggest that the same cause (probably pyramidal deficits) may be involved in both of them. Eur J Neurol 5:579-585 (C) 1998 Lippincott Williams & Wilkins.