Upbeat Nystagmus and Cerebellar Atrophy in a Patient with Parkinson’s Disease

Abstract

　To the best of our knowledge, upbeat nystagmus (UBN) has not been reported before in patients with Parkinson's disease (PD). There are also very few reports of cerebellar atrophy in patients with PD. A-60-year-old woman with a 10-year history of PD visited our hospital for deep brain stimulation therapy for her camptocormia. Neurological examination revealed not only the core signs of PD (rigidity, resting tremor, postural instability), but also UBN. ¹²³I-metaiodobenzylguanidine (MIBG) myocardial scintigraphy revealed markedly diminished uptake of MIBG, strongly supporting the clinical diagnosis of PD. Brain MRI revealed prominent cerebellar atrophy, while the brainstem was preserved. ENG showed that the UBN was observed at the primary eye position and enhanced during upward gaze in the light, but not during downward gaze. In addition to UBN, several other abnormal ENG findings were also observed, including horizontal gaze-evoked nystagmus and rebound nystagmus. Secondly, both horizontal and vertical pursuits were disturbed and horizontal OKN was poorly induced. Lastly, the horizontal saccade was relatively hypometric, while the upward saccades were slight hypermetric. Although the pathogenesis of UBN in this patient still remains unclear, UBN is known to be mainly caused by dysfunction of the velocity-to-position integrator caused by pontomedullary lesions or pontomesencephalic lesions. Alternatively, cerebellar control over this integrator is presumably disrupted by lesions in the cerebellum itself or lesions in the cerebellar neural circuits. As for the pathogenesis of UBN in our case, pontomedullary lesion was first suspected, because, besides the abovementioned ENG findings, most cases of UBN reported in the literature are caused by medullary lesions, including lesions of both the medial vestibular and prepositus hypoglossi nuclei, which play an important role as the velocity-to-position integrator. In addition, dysfunction of the vestibular cerebellum was also suspected as a cause, judging from the cerebellar atrophy and other abnormal ENG findings. In conclusion, it is necessary to consider dysfunction of the vestibular cerebellum as a cause of abnormal eye movements in PD, not to mention dysfunction of the brainstem.