From the Guidelines
Lateral nystagmus is typically diagnosed using the supine roll test, which is the preferred maneuver to diagnose lateral canal BPPV, as recommended by the 2017 clinical practice guideline update 1. The supine roll test is performed by initially positioning the patient supine with the head in neutral position followed by quickly rotating the head 90 degrees to one side with the clinician observing the patient’s eyes for nystagmus. After the nystagmus subsides (or if no nystagmus is elicited), the head is then returned to the straight faceup supine position. Some key points to consider when evaluating lateral nystagmus include:
- The direction, frequency, and amplitude of nystagmus provide important diagnostic clues - jerk nystagmus (quick movement in one direction, slow return) suggests peripheral vestibular issues, while pendular nystagmus (equal velocity in both directions) often indicates central nervous system disorders.
- Lateral canal BPPV accounts for 5% to 15% of BPPV cases, and the etiology is also felt to be due to the presence of abnormal debris within the lateral canal, but the pathophysiology is not as well understood as that of posterior canal BPPV, as noted in the 2017 guideline update 1.
- The 2017 clinical practice guideline update recommends that clinicians should diagnose lateral semicircular canal BPPV when vertigo associated with horizontal nystagmus is provoked by the supine roll test, as stated in the guideline 1.
- Patients experiencing lateral nystagmus should seek medical evaluation promptly as it may indicate serious neurological conditions, and clinicians should reassess patients within 1 month after an initial period of observation or treatment to document resolution or persistence of symptoms, as recommended in the 2017 guideline update 1. The most recent and highest quality study, the 2017 clinical practice guideline update 1, provides the best evidence for the diagnosis and management of lateral nystagmus.
From the Research
Definition and Types of Nystagmus
- Nystagmus is defined as rhythmic, most often involuntary eye movements, consisting of a slow drift of the eyes followed by a fast central compensatory movement back to the primary position (refixation saccade) 2.
- The direction of nystagmus is reported according to the fast phase.
- There are two major categories of nystagmus: spontaneous nystagmus (e.g., upbeat or downbeat nystagmus) and nystagmus induced or modified by certain factors (e.g., gaze-evoked nystagmus, head-shaking nystagmus, positional nystagmus) 2.
Lateral Nystagmus
- Lateral nystagmus is not explicitly defined in the provided studies, but it can be inferred to be a type of nystagmus where the fast phase is directed laterally.
- Gaze-evoked nystagmus, which can be lateral, is mentioned as a type of nystagmus that occurs when the eyes are moved from the primary position 2, 3.
Diagnosis and Treatment
- The diagnosis of nystagmus involves characterizing the type of nystagmus and its visual effects 3.
- Treatment options for nystagmus include pharmacological, optical, and surgical approaches 4, 5.
- For example, acquired periodic alternating nystagmus can be treated with baclofen, and downbeat nystagmus can be treated with aminopyridines 4, 6.
- In some cases, treatment with gabapentin, memantine, or base-out prisms can be helpful in reducing nystagmus and improving visual acuity 4, 5.