Autonomic instability, as measured by pupillary unrest is not associated with multiple sclerosis fatigue severity

Multiple sclerosis (MS) fatigue is one of the most common symptoms in MS, but its pathophysiology is still not understood. Sympathovagal imbalance was suggested as a reason for fatigue in chronic fatigue syndrome. We examined the role of an imbalance in the central autonomic nervous system (ANS) as a cause of MS fatigue in 51 MS patients and a control group of 22 healthy volunteers. Fatigue was assessed with the revised MS Fatigue Severity Scale (FSS) and the Modified Fatigue Impact Scale (MFIS). Depression was evaluated with the Beck Depression Inventory (BDI). Disintegration of the central ANS expressed by pupillary fatigue waves was measured with pupillography and documented in the pupillary unrest index (PUI). All subjects had less than five points on the seven-point Stanford Sleepiness Scale and were therefore not sleepy. MS patients had significant higher mean FSS scores (p = 0.001) and mean MFIS scores (p = 0.003) than our control group. Mean BDI scores were significant higher (p = 0.001) in the MS group, but were in the lowest score range (0-10 points) in both groups. Surprisingly, we found a statistically significant inverse correlation between PUI values and either FSS scores (p = 0.001; r = -0.521) or MFIS scores (p = 0.002; r = -0.423) in the MS group, but not in healthy participants. We therefore conclude that autonomic instability, as measured by pupillary unrest is not associated with MS fatigue severity.