77 巻 (2018) 2 号 p. 77-87
An 82-year-old man was referred to our hospital complaining of postural instability leading to early unexplainable falls. Neurological examinations revealed horizontal gaze nystagmus, impairment of vertical gaze, abnormal eye movements such as square wave jerks and slow saccade, remarkable nuchal rigidity, mild rigidity of all four limbs, akinesia, dysarthria, slight dysphagia, and dementia. MRI/CT findings showed remarkable symmetrical atrophy of the frontal and temporal lobes, remarkable dilation of both lateral ventricles and the third ventricle. Atrophy of the posterior vermis in the cerebellum was also noticed. SPECT (123I-IMP single photo emission CT) findings revealed reduction of the blood flow to both the frontal and temporal lobes. From these findings, he was diagnosed as having frontotemporal dementia (FTD) caused by progressive supranuclear palsy (PSP). The characteristic electronystagmography (ENG) findings were as follows: (1) abnormal eye movements such as square wave jerks were recognized in the light; (2) transitory alternating saccade (TAS) in the dark: in other words, like a sine wave curve, the eye position deviated rhythmically to either lateral side with a periodicity of 0.2-0.3 Hz. Associated with this deviation was 2-8 saccades (about 2°) with each oscillation; (3) complete impairment of vertical smooth pursuit, while the horizontal pursuit was intermingled with back-up saccade (cogwheel-pursuit); (4) Either horizontal or vertical OKN were scarcely induced; Finally, (5) Vestibular caloric nystagmus was poorly induced bilaterally. Visual suppression of caloric nystagmus deteriorated remarkably bilaterally. On the contrary, caloric nystagmus was enhanced during fixation in light.
To the best of our knowledge, there are no clinical reports in the literature on TAS in a case with FTD-PSP. Although the definite mechanism of TAS still remains unclear, the impairments to the vestibulocerebellar function (posterior vermis or fastigial nucleus) could be apparently responsible for these abnormal eye movements.