Dynamics of saccade parameters in multiple sclerosis patients with fatigue

Fatigue is one of the most frequent and disabling symptoms in multiple sclerosis (MS). Its pathophysiology remains poorly understood and objective measures to quantify fatigue are unavailable to date. To investigate whether analysis of ocular motor movements can provide diagnostic information in MS patients with fatigue, 37 MS patients (21 female, age 44 ± 9 years) and 20 age- and gender-matched healthy controls were prospectively recruited. Fatigue was assessed with the fatigue severity scale (FSS). Twenty-five MS patients were fatigued (defined as FSS ≥ 4) and 12 MS patients were not. Subjects performed a saccadic fatigue task that required execution of uniform saccades over a period of 10 min. Saccadic amplitude, latency and peak velocities during the task were analysed and selected parameters were tested in a receiver operating characteristic (ROC) analysis. Fatigued patients showed a significantly larger decrease of saccadic peak velocity and amplitude when compared to patients without fatigue and healthy controls. Furthermore, fatigued patients showed significantly longer latencies compared to non-fatigued patients and healthy controls. Peak velocity change over time and latencies correlated with FSS scores. The best parameter to discriminate between fatigued and non-fatigued patients was peak velocity change over time (ROC; area under the curve = 0.857). Assessment of peak velocity, amplitude and latency in a saccade fatigue task is a promising approach for quantifying fatigue in MS patients.