Positional nystagmus testing determines whether a change of position of the patient’s vestibular systems in space provokes nystagmus. Some nystagmus is only evident with changes in head position with respect to gravity. Both central and peripheral vestibular lesions can cause positional nystagmus and vertigo, and the examination focuses on distinguishing the two.
Most central positional nystagmus is static, in that the nystagmus persists as long as the head is kept in the provoking position. Nystagmus produced as a result of benign paroxysmal positional vertigo (BPPV), a peripheral vestibular pathology, is usually transient. Observations of the direction, latency and fatigability of nystagmus are important diagnostically.
“I am going to place goggles over your eyes. I will then assist you in moving into different positions. It is important to keep your eyes open at all times so that the cameras can record your eye movement. I will also ask you some questions to help keep you alert during the test.”
Used to rule out spontaneous nystagmus. The patient is in the seated position on the table with vision denied.
The patient is lying on the table, vision denied, while his head is supported by the examiner and elevated at approximately 30º (the approximate position of the head relative to the body in its natural state).
Begin with the patient in the supine position described above. Gently guide the patient’s head to one side. Allow adequate time for nystagmus to occur (approximately 15 seconds). If no nystagmus occurs, return the patient’s head to the center, and then turn the patient’s head in the opposite direction and repeat procedure. If nystagmus is noted in either the head right or head left positions, immediately ask the patient to roll onto his shoulder toward the side of the affected ear.
If the patient does not have any form of positional nystagmus, the tracing will result in essentially a flat line for each position. The bar graphs for left and right beating nystagmus and down and up beating nystagmus will display as zero for all conditions (Figures 1a-c).
If positional nystagmus is present, nystagmus will be present in the horizontal and/or vertical channels. The nystagmus is represented by the triangles or green segments in the tracing and the averaged values for the strongest 10 seconds are shown in the bar graphs to the right of the tracing for each position (Figures 2a-c and 3).
Nystagmus that persists as long as the provoking position is maintained can occur with either central or peripheral vestibular lesions. Review of the waveforms is helpful. Pure downbeat nystagmus from central lesions is often accentuated in the reclining position, and sometimes may only be noted with this position. The lack of a torsional component differentiates this from anterior canal BPPV. Pure upbeat nystagmus can be positional. Positional torsional nystagmus has been reported with lateral medullary infarction.
Other features that indicate central disease are lack of latency, lack of fatigability, and the inability to suppress nystagmus with vision. Patients with static positional nystagmus without prior evidence of more typical BPPV should be investigated for central disease. Lesions of the cerebellar vermis are especially associated with static positional nystagmus.
Alcohol can induce a static positional vertigo and horizontal nystagmus. Nystagmus beating towards the floor when the patient’s head is lying flat on its side emerges within 30 minutes of ingestion, peaking at 2 hours. As the blood alcohol level falls, 4 to 5 hours later, the nystagmus recurs in the opposite direction, and may last up to 12 hours. It is attributed to more rapid diffusion of alcohol into the cupula than the endolymph. The resulting difference in specific gravity temporarily imparts an abnormal sensitivity to linear acceleration, such as gravity.
For a complete discussion of positional testing and protocols, refer to:
Jacobson, GP, and Shepard, NT. Balance Functional Assessment and Management, 2nd Ed. San Diego; Plural Publishing, 2015
*NOTE: This is intended only as a guide, official diagnosis should be deferred to the patient’s physician.