The Floccular Syndrome: Dynamic Changes in Eye Movements and Vestibulo-ocular Reflex in Isolated Infarction of the Cerebellar Flocculus

The cerebellar flocculus is a critical structure involved in the control of eye movements. Both static and dynamic abnormalities of the vestibulo-ocular reflex (VOR) have been described in animals with experimental lesions of the flocculus/paraflocculus complex. In humans, lesions restricted to the flocculus are rare so they can become an exceptional model to contrast with the clinical features in experimental animals or in patients with more generalized cerebellar diseases. Here, we examined a 67-year-old patient with an acute vestibular syndrome due to an isolated infarct of the right flocculus. We evaluated him multiple times over 6 months-to follow the changes in eye movements and vestibular function-with caloric testing, video-oculography and head-impulse testing, and the anatomical changes on imaging. Acutely, he had an ipsilateral-beating spontaneous nystagmus, bilateral gaze-evoked nystagmus, borderline impaired smooth pursuit, and a complete contraversive ocular tilt reaction. The VOR gain was reduced for head impulses directed contralateral to the lesion, and there was also an ipsilesional caloric weakness. All abnormalities progressively improved at follow-up visits but with a considerable reduction in volume of the affected flocculus on imaging. The vestibular and ocular motor findings, qualitatively similar to a previously reported patient, further clarify the "acute floccular syndrome" in humans. We also add new information about the pattern of recovery from such a lesion with corresponding changes in the size of the affected flocculus on imaging.