On videonystagmography (VNG), a patient shows unidirectional horizontal nystagmus that increases with gaze in the direction of fast phase (Alexander's Law) and is inhibited by visual fixation. This pattern suggests:

• A Central vestibular lesion
• B Benign paroxysmal positional vertigo (BPPV)
• C Perilymph fistula
• D Peripheral vestibular lesion (unilateral hypofunction) ✓

Explanation

A peripheral vestibular lesion produces spontaneous nystagmus that follows Alexander's Law (intensity increases when gaze is in the direction of the fast component), is suppressed by visual fixation (cerebellum remains intact), and is unidirectional horizontal-torsional. Central lesions produce nystagmus that does not obey Alexander's Law, is not inhibited by fixation, may be direction-changing, and may be purely vertical or purely torsional. These features help differentiate peripheral from central vestibular pathology on VNG.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.