The mechanism by which they suppress downbeat nystagmus is unclear, although they might work by altering the firing of cerebellar Purkinje cells. Both drugs are well tolerated, although they can cause seizures (usually in patients with a predisposition to epilepsy who are given high dosages) and cardiac arrhythmias in patients with QT interval prolongation. 4-aminopyridine appears to be more effective than 3,4-diaminopyridine. 3,4-diaminopyridine and 4-aminopyridine have been shown to suppress downbeat nystagmus, although they are more effective in patients with cerebellar degenerations and less effective in those with focal cerebellar lesions. ![]() Recent trials have demonstrated that the aminopyridine potassium channel blockers are effective for downbeat nystagmus. However, a prospective double-masked trial showed that trihexyphenidyl produced only a modest improvement with significant side-effects. Anticholinergics have been suggested as a potential treatment. Gabapentin, now thought to act as an α2δ-1 calcium channel antagonist and N-methyl-D-aspartate (NMDA) receptor antagonist, did not consistently improve downbeat nystagmus in the same trial. Baclofen, a GABAB-agonist, was thought to suppress downbeat nystagmus, but did not produce a consistent benefit in a double-masked trial. Clonazepam, a GABAA-agonist, has been shown to improve downbeat nystagmus in two uncontrolled trials. Peripheral Vestibular Nystagmus Downbeat Nystagmusĭownbeat nystagmus is common and often causes disabling visual symptoms (e.g., vertical oscillopsia). Consequently, the patient is best managed with treatments directed towards the underlying disorder. The associated vertigo, nausea, and vomiting are often more distressing to the patient than are the visual symptoms from the nystagmus. In most cases, the nystagmus is short-lived or intermittent. Nystagmus can result from peripheral vestibular diseases, such as vestibular neuritis, Ménière’s disease, and benign paroxysmal positional vertigo. ![]() Table 2: Drug Treatments for Acquired NystagmusĪbbreviations: bid, twice daily MS, multiple sclerosis OPT, oculopalatal tremor qid, four times daily tid, three times daily Nystagmus Type
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