Objective: The diagnosis of central paroxysmal positional nystagmus (CPPN) is challenging, and the mechanisms require further elucidation. This study aimed to determine the characteristics and mechanisms of CPPN. Methods: Seventeen patients with CPPN were subjected to analyses of their clinical findings, MRI lesions, and oculographic data on spontaneous and positional nystagmus. Results: The direction of CPPN was mostly aligned with that of the head motion during the positioning, and 3 types of CPPN were identified: downbeat nystagmus on straight-head hanging, upbeat nystagmus on uprighting, and apogeotropic nystagmus during supine head roll test. The direction of CPPN was aligned with the vector sum of the rotational axes of the semicircular canals that were normally inhibited during the positioning. The intensity of evoked nystagmus was at its peak initially and then decreased exponentially over time. The time constants (TC) of the vertical CPPN ranged from 3 to 8 seconds, which corresponds to the TC of the vertical rotational vestibulo-ocular reflex. Sixteen patients (94.1%) showed more than one type of CPPN. Furthermore, persistent downbeat or apogeotropic positional nystagmus was associated in 11 patients (64.7%). Most patients with CPPN from a circumscribed brain lesion showed an involvement of the cerebellar nodulus or uvula. Conclusion: CPPN may be ascribed to enhanced responses of the vestibular afferents due to lesions involving the nodulus and uvula. CPPN could be differentiated from benign paroxysmal positional nystagmus by positional nystagmus induced in multiple planes, temporal patterns of nystagmus intensity, and associated neurologic findings suggestive of central pathologies.

Background: Vestibular symptoms/signs frequently coexist with migraine, but the mechanisms of migraine-related vestibular dysfunction remain to be elucidated. This study aimed to determine altered brain metabolism in vestibular migraine. Methods: Two patients with vestibular migraine underwent ¹⁸F-fluorodeoxy glucose (FDG) positron-emission tomography (PET) during and between attacks of vestibular migraine in addition to detailed neurotological evaluation. We analyzed the regional brain metabolism of the patients in comparison with that of age-matched healthy controls in each patient. We also compared ictal with interictal FDG PET using a subtraction method. Results: During the attacks, both patients showed an activation of the bilateral cerebellum and frontal cortices, and deactivation of the bilateral posterior parietal and occipitotemporal areas. One patient also showed hypermetabolism in the dorsal pons and midbrain, right posterior insula, and right temporal cortex while the other patient had an additional activation of the left temporal cortex. Compared with interictal images, ictal PET showed increased metabolism in the bilateral cerebellum, frontal cortices, temporal cortex, posterior insula, and thalami. Conclusion: During the attacks of vestibular migraine, the increased metabolism in the temporo-parieto-insular areas and bilateral thalami indicates activation of the vestibulo-thalamo-cortical pathway, and decreased metabolism in the occipital cortex may represent reciprocal inhibition between the visual and vestibular systems.

Lee SH, et al. J Clin Neurol. 2010 Jun;6(2):51-63. http://dx.doi.org/10.3988/jcn.2010.6.2.51