What is the cause of horizontal nystagmus (abnormal involuntary eye movements)?

From the Guidelines

Horizontal nystagmus is most commonly associated with benign paroxysmal positional vertigo (BPPV), particularly the lateral semicircular canal type, and can be diagnosed using the supine roll test, as recommended by the 2017 clinical practice guideline update 1. The evaluation of horizontal nystagmus should include a thorough neurological examination, with attention to other eye movements and balance testing. Diagnostic workup may require further testing, but according to the guideline, radiographic imaging and vestibular testing are not recommended unless the diagnosis is uncertain or there are additional symptoms or signs unrelated to BPPV that warrant testing 2, 3. The treatment of horizontal nystagmus targets the underlying cause, and for vestibular causes, canalith repositioning procedures (CRPs) are recommended as the initial therapy for posterior canal BPPV, while observation or vestibular rehabilitation may be considered for lateral canal BPPV 4, 5. Some key points to consider in the management of horizontal nystagmus include:

• Differentiating BPPV from other causes of imbalance, dizziness, and vertigo
• Assessing patients for factors that modify management, such as impaired mobility or balance, central nervous system disorders, lack of home support, and increased risk for falling
• Reassessing patients within 1 month after an initial period of observation or treatment to confirm symptom resolution
• Evaluating patients with persistent symptoms for unresolved BPPV or underlying peripheral vestibular or central nervous system disorders
• Counseling patients regarding the impact of BPPV on their safety, the potential for disease recurrence, and the importance of follow-up. The direction, speed, and other characteristics of the nystagmus often provide valuable diagnostic clues about the location and nature of the underlying problem, and the 2017 guideline update provides a comprehensive approach to the diagnosis and management of BPPV, including horizontal nystagmus 1, 2.

From the Research

Horizontal Nystagmus

• Horizontal nystagmus can be observed in various central and peripheral vestibular disorders, including canalolithiasis, cupulolithiasis, and other vestibulopathies 6
• The temporal and intensity profile of horizontal positional nystagmus can be helpful in separating these entities 6
• Direction-changing horizontal positional nystagmus can be observed in a variety of central and peripheral vestibular disorders 6
• Persistent geotropic or apogeotropic horizontal nystagmus can be seen in patients with vestibular migraine (VM) 6
• Horizontal nystagmus can also be associated with other conditions, such as Meniere's disease, vestibular schwannoma, and unilateral or bilateral peripheral vestibular loss 6

Diagnosis and Characteristics

• The diagnosis of horizontal nystagmus involves a thorough clinical evaluation, including a structured description of the nystagmus, its three-dimensional beating direction, trigger factors, and duration 7
• The HINTS (head impulse, nystagmus, and test of skew) examination can be used to determine the cause of acute vestibular syndrome, with good sensitivity and reasonable specificity for diagnosing a central cause 8
• The HINTS Plus examination, which includes an additional assessment of auditory function, can also be used to diagnose central causes of acute vestibular syndrome 8

Treatment and Management

• The treatment of horizontal nystagmus depends on the underlying cause, and may involve disease-specific therapies, pharmacotherapy, strabismus surgery, or prisms to shift null points 9
• Medical management with aminopyridines has become first-line therapy for downbeat nystagmus, in addition to disease-specific therapies 9
• Behavioural changes and general therapeutic options, such as enhancing Purkinje cell function, can also be used to manage horizontal nystagmus 9