両側前庭障害のためCANVASと鑑別を要したSCA6の一例

抄録

The present case report documents the case of an 83-year-old female patient who was diagnosed as having spinocerebellar ataxia type 6 (SCA6). The patient was initially suspected as having cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS) due to the severe bilateral vestibular disorder. She had experienced unsteadiness and slurred speech for years. During the neurologist consultation, it was determined that she was exhibiting symptoms of cerebellar ataxia. The patient had a negative family history of cerebellar ataxia. A comprehensive clinical evaluation revealed the presence of gaze-evoked nystagmus, saccadic pursuit, and diminished vibration sense in the lower limbs. No spontaneous, positional, or positioning nystagmus was observed. The hearing test revealed only age-appropriate sensorineural hearing loss. Brain MRI revealed mild cerebellar atrophy. The video head impulse test (vHIT) showed decreased vestibulo-ocular reflex (VOR) gain in all semicircular canals on both sides. As the findings were possibly suggestive of CANVAS, genetic testing was performed, which revealed that the diagnosis was not CANVAS, but rather SCA6.

In cases of SCA6, cerebellar ataxia and any type of nystagmus are common, as seen in the CANVAS study, but bilateral vestibular disorder has never been reported. Our case underscores the need to bear in mind the possibility of vestibular disorders even in patients with SCA6.