If we are assessing a patient with a vestibular dysfunction, and we perform the hall-pike dix test and the patient has nystagmus present on both the L and R that is unidirectional, is it a peripheral dysfunction? If they had nystagmus that was bi-directional at both the L or R would this be central? I am having trouble deciphering if peripheral is strictially positional and both those scenarios would make the answer peripheral where as central the nystagmus would not be altered.

Nystagmus can be defined as a repetitive, involuntary, to-and-fro oscillation of the eyes. It may be physiological or pathological and may be congenital or acquired. Nystagmus may be described as symmetrical, asymmetrical, bilateral or unilateral (this is rare and is usually actually asymmetrical but more evident on one side). It may be conjugate (both eyes move together) or disconjugate (the eyes appear to move independently of each other). [1]

Patients with peripheral vestibular nystagmus typically present with a sudden, sometimes dramatic, onset of dysequilibrium with vertigo, nausea, and vomiting. Patients often recognize that their symptoms are worsened by particular head movements or postures. Oscillopsia, tinnitus, and hearing loss may also occur. After the acute phase of peripheral vestibular loss, which typically lasts days, patients experience a slow period (weeks to months) of gradually waning symptoms. Even patients who become asymptomatic may experience discomfort months to years later, when their vestibular system is challenged, as when riding in a fast-moving car or boat.

Peripheral vestibular nystagmus occurs in patients with dysfunction of the end organ (semicircular canals, otolithic structures, vestibular nerve). End-organ damage, which is usually unilateral disrupts the otherwise symmetric vestibular afferent inputs to the brain which stabilizes eye position in eccentric locations. This loss of tonic symmetry produces a directional bias in eye position. A reduction in input from a left-sided vestibular lesion, for instance, produces a leftward bias, which then induces a corrective saccade away from the side of the lesion. Thus, a left-sided lesion would produce leftward slow phases and right jerk nystagmus. [2]

Central nystagmus occurs as a result of either normal or abnormal processes not related to the vestibular organ. For example, lesions of the midbrain or cerebellum can result in up- and down-beat nystagmus. Nystagmus is occasionally associated with vertigo. [3]

The Dix–Hallpike test is a diagnostic maneuver used to identify benign paroxysmal positional vertigo (BPPV). Patients are lowered quickly to a supine position, with the neck extended by the clinician performing the maneuver. A positive test is indicated by patient report of a reproduction of vertigo and clinician observation of nystagmus (either unidirectional or bidirectional or in either 1 or both eyes). A positive test is typically indicative of a peripheral nystagmus. If the test is negative, it makes benign positional vertigo a less likely diagnosis and central nervous system involvement should be considered for the complaints of nystagmus. [4]

Reference 1, Reference 2, Reference 3, Reference 4