Timothy C. Hain, MD Page last modified: January 5, 2008
Upbeating nystagmus describes an eye condition in which the eyes drift downward and make upward corrective movements (beats). Here we are mainly discussing upbeating nystagmus that occurs in persons who are sitting upright, and that have their eyes in the center (primary position).
For those who like to get to the meat quickly, there is usually not very much to learn from weak upbeating nystagmus, but strong upbeating nystagmus is usually caused by brainstem damage.
|Upbeating nystagmus is shown on the bottom panel of the figure to the left.|
Upbeat nystagmus is found in smokers as a side effect of nicotine, in persons with alcohol intoxication (Fetter et al, 1999) and as a side effect of medications. For example, some of the SSRI type antidepressents seem to be associated with upbeating nystagmus. Migraine can, of course, cause nearly any nystagmus. This type of UBN is generally suppressed by fixation. These benign associations are far more common than serious brainstem disease.
Common causes of UBN, usually suppressed by fixation, and usually of no significance:
Uncommon causes of UBN, which may be visible with fixation
Strong primary position upbeat nystagmus has been described in lesions of the medulla, the ventral tegmentum, the anterior vermis of the cerebellum, and the adjacent brachium conjunctivum and midbrain. UBN has been reported in association in specific disorders such as Wernicke's encephalopathy, multiple sclerosis, brainstem infarction and other lesions. In the author's experience with Wernicke's, the nystagmus has a peculiar increase on downgaze (one would expect the opposite). Presumably this would implicate the neural integrator which controls gaze holding.
Supplemental material on the site DVD: Video of upbeating nystagmus due to Wernicke's encephalopathy.
While UBN is generally caused by midline lesions, cases have been reported in unilateral medial midbrain lesions. Hirose and others (1998) have proposed that in this instance, UBN may be caused by a lesion in the nucleus intercalatus of Staderini, one of the three subnuclei of the perihypoglossal nucleus (others include the nucleus of Roller, the nucleus prepositus hypoglossi which performs neural integration for the horizontal oculomotor system).
Ranalli and Sharpe (1988) suggested that some forms of UBN were explained by disruption of the ventral tegmental pathway for the upward VOR (vestibulo-ocular reflex), causing imbalance in the vertical VOR.
Upbeat nystagmus can be modulated by convergence, changing into downbeat, when it occurs congenitally as well as when associated with Wernicke's. This has been reported by Cox and others (1981).