Conditions associated with tumours of the cerebellopontine angle, such as neurofibromatosis type 2, may cause a combination of:

1. Low frequency, large amplitude gaze evoked horizontal nystagmus looking ipsilaterally (towards the lesion), because of defective gaze holding dur to compression of brainstem structures
2. High frequency, small amplitude nystagmus on looking contralaterally because of vestibular imbalance (Bruns’ nystagmus) ¹.

Note that according to Alexander’s law, the nystagmus caused by a peripheral lesion is more intense when gaze is directed toward the side of the fast phase².

Similarly, asymmetric lesions affecting both the vestibular nucleus and nucleus prepositus hypoglossi can cause a combination of vestibular and gaze-evoked nystagmus respectively².

(vv)Brun.mp4(tt)

From: Pavlovic D. Brun's nystagmus. https://www.youtube.com/watch?v=C86JKb670iw

(vv)Brun2.mp4(tt)

From: Biswas SN, Ray S, Ball S, Chakraborty PP. Bruns nystagmus: an important clinical clue for cerebellopontine angle tumours. BMJ Case Rep. 2018;2018:bcr2017223378. Published 2018 Jan 17. doi:10.1136/bcr-2017-223378