Alcohol Intoxication is the Most Likely Cause of the Nystagmus
The repetitive horizontal eye movements (gaze-evoked nystagmus) in this patient are most likely caused by alcohol intoxication, given his consumption of 10 beers daily and alcohol on breath at presentation. 1
Pathophysiology of Alcohol-Induced Nystagmus
Alcohol causes gaze-evoked nystagmus (GEN) by inducing transient cerebellar dysfunction, resulting in a two-fold increase in centripetal eye-drift velocity at eccentric gaze positions. 1
The mechanism involves alcohol rendering the cupula lighter than endolymph (buoyancy hypothesis), making it sensitive to gravity and producing positional alcohol nystagmus with characteristic horizontal components. 2
Alcohol at blood concentrations of 0.05-0.1% significantly impairs the slow eye movement system, producing horizontal gaze nystagmus that is the basis for field sobriety testing. 3, 4
Why the Other Options Are Less Likely
Ear Infection (Option 2)
While acute otitis media with serous labyrinthitis can cause nystagmus, the most common pattern is direction-fixed irritative-type nystagmus (in 8 of 9 cases), not simple horizontal gaze-evoked nystagmus. 5
Labyrinthitis-associated nystagmus typically presents with vertigo as a prominent feature and may show direction-changing positional patterns in supine head-roll testing. 5
The clinical context of heavy daily alcohol consumption with alcohol on breath makes this a less parsimonious explanation. 1
Dehydration (Option 3)
Dehydration causes dry mucous membranes but does not directly produce gaze-evoked nystagmus through any established pathophysiologic mechanism. 6
While dehydration may be present (evidenced by dry mucous membranes), it does not explain the specific ocular motor finding of horizontal nystagmus. 6
Sinusitis (Option 4)
Upper respiratory infections and sinusitis do not cause gaze-evoked nystagmus through direct mechanisms.
There is no established pathophysiologic link between sinusitis and the cerebellar/vestibular dysfunction required to produce GEN. 7
Clinical Recognition Pattern
Gaze-evoked nystagmus is definitively a central form of nystagmus indicating brainstem or cerebellar pathology, and alcohol is a well-established cause of transient cerebellar dysfunction. 7
The nystagmus pattern from alcohol intoxication matches that seen in patients with cerebellar degeneration, characterized by increased centripetal eye-drift with centrifugal correcting saccades at eccentric gaze. 1
Central nystagmus (including alcohol-induced GEN) typically does not fatigue and is not easily suppressed by visual fixation, distinguishing it from peripheral vestibular causes. 7
Critical Clinical Caveat
While alcohol is the most likely cause in this specific clinical scenario, if the nystagmus persists after alcohol metabolism or if other neurological signs develop, neuroimaging (preferably MRI) should be obtained to evaluate for structural brainstem or cerebellar lesions. 7, 8