Bruns’ Nystagmus and Positive Head Impulse Tests in Platybasia

Platybasia, flattening of the skull base, causes upward displacements of the odontoid process through the foramen magnum (basilar invagination), which reduces the space of the posterior fossa.1 Platybasia mostly produces headaches induced by coughing, lower cranial nerve palsies, pyramidal signs, syringomyelia, and hydrocephalus.1 Despite about a quarter of patients with platybasia experiencing vertigo,2 detailed descriptions on the neuro-otologic findings are not available in the literature. [...]our patient shows that those findings can be observed in other lesions that may cause both vestibular imbalance and integration failure.3 The spontaneous nystagmus from unilateral vestibular deficits has a linear slow phase, and usually follows Alexander’s law, which makes the nystagmus increase with gaze into the contralesional side. Whereas unilateral peripheral vestibular lesion usually produces a positive head impulse response to the lesion side, our patient showed bilaterally decreased gains of the vestibulo-ocular reflex during head impulses in the presence of normal caloric responses.