Optokinetic After-Nystagmus: A Marker for Migraine? A Prospective Observational Study.

INTRODUCTION

Vestibular migraine (VM), particularly its chronic variant, poses a diagnostic challenge. Patients suffering from VM may not have the characteristic headaches associated with the dizziness. In these cases, a marker for migraine pathology in general could help appropriately diagnose certain types of dizziness as migrainous despite these patients not meeting current diagnostic criteria for VM. Migraine patients in general (headache and vestibular) are known to share a tendency toward intolerance of certain stimuli, including busy visual stimuli. True optokinetic stimulation, measured by the production of optokinetic after-nystagmus (OKAN) simulates these busy visual stimuli.

METHODS

Prospective observational study comparing response to optokinetic stimulation between migraine patients and controls. Questionnaires regarding general sensitivities to busy visual stimuli were completed prior to beginning the study. Both subjective and objective markers of stress were measured before and after exposure to the stimulus. Initial slow-phase velocity, slow cumulative eye position, and adjusted time constant of OKAN were compared between the 2 groups.

RESULTS

The groups differed only with regard to sensitivity to blinking lights and history of motion sickness on initial questionnaire. Regarding subjective symptoms of discomfort, migraine patients tended to report higher scores than controls both before and after testing, but there was no significant difference from before to after stimulus in each group's scores. There were no statistically-significant differences between initial slow-phase velocity, slow cumulative eye position, and adjusted time constant of OKAN between groups.

CONCLUSIONS

In this study, OKAN measurements were not useful in differentiating migraine patients at large from control subjects. We hypothesize that there may be a distinct subgroup of migraine patients that are more sensitive to visually-disturbing situations that may differ from other migraine sufferers. Future studies will aim to identify such patients and compare them to controls.