Downbeat nystagmus and other characteristic ENG findings in a case with paraneoplastic cerebellar degeneration (PCD)

A-60-year-old woman presented with a 6-month history of progressive coordination imbalance with gait disturbance, until she became obliged to use a cane for walking. Neurological examination revealed a cerebellar syndrome with limb, trunk and gait ataxia and downbeat nystagmus (DBN). MRI showed cerebellar atrophy, especially of the cerebellar vermis. CSF examination was negative for both oligoclonal bands and myelin basic protein. Serology for anti-YO antibodies was positive, which led us to make the diagnosis of paraneoplastic cerebellar degeneration (PCD). Eventually, abdominal ultrasonography revealed left ovarian cancer. After total hysterectomy, bilateral oophorectomy, partial omentectomy, and periaortic lymphadenectomy, the patient became able to walk again without assistance. The characteristic ENG findings were as follows: (1) In the light/dark, DBN was observed mainly during rightward gaze, and less prominently at the primary position and during leftward gaze. (2) However, when the patient lay in the supine posture, the DBN totally disappeared, even during rightward gaze. (3) Both horizontal and vertical pursuits revealed saccadic pursuit. (4) The peak slow-phase velocities and frequency of horizontal OKN were markedly reduced. (5) The horizontal OKAN disappeared bilaterally. (6) Hypermetric saccades, overshoot, were observed in both the horizontal and vertical directions. (7) Caloric nystagmus was well-induced bilaterally, although the visual suppression (VS) ratio was markedly reduced bilaterally. The above ENG findings suggest mainly impairment of the cerebellar systems, but also some dysfunction of the velocity storage systems. Presumably, impairment of smooth pursuit was derived from a lesion of the flocculus/paraflocculus, vermis and cerebellar hemispheres. As for dysfunction of the velocity storage systems, it is considered that the velocity storage integrators themselves in the brainstem were still intact. Rather, conceivably, the visual-vestibular interaction could not function well in the velocity storage systems because of insufficient supply of visual inputs from the impaired vestibular cerebellum.