Autonomic involvement in multiple sclerosis: a pupillometric study.

To study pupillary autonomic function in multiple sclerosis (MS), we examined 36 subjects with low disability, preserved visual acuity and no recent history (2 years) of optic neuritis or actual visual complaints. Compared to controls, MS patients showed a greater dilatator reaction with darkness and, for the light reflex, a lower amplitude and contraction rate and a greater recovery of pupillary diameter 5 s after the stimulus. Within the MS group, no difference was found comparing patients with or without the following characteristics: nuclear magnetic resonance imaging evidence of midbrain lesions; increased visual evoked potential P100 latency; and a previous history of optic neuritis. No correlation was found between P100 latency, duration of disease and pupillometric parameters. Our results indicate that in MS patients there is autonomic dysfunction with a reduction of parasympathetic tone and a relative increase in sympathetic dilatator tone to the pupils. We suggest that pupillary abnormalities could be due to non-specific impairment of the central pathways subserving pupil functions.