Role of clonazepam in the treatment of idiopathic downbeat nystagmus.

OBJECTIVE/HYPOTHESIS: Downbeat nystagmus is defined as spontaneous nystagmus present with fixation in the primary position or lateral gaze. Those who have downbeat nystagmus but negative magnetic resonance imaging results are termed as idiopathic. Patients with idiopathic downbeat nystagmus, although unconcerned with their etiology, have visual symptoms such as oscillopsia, diplopia, or blurred vision. The purpose of this study is to evaluate the efficacy of clonazepam in treating idiopathic downbeat nystagmus.
METHODS: Patients with downbeat nystagmus were rechecked by electronystagmography (ENG); then 0.5 mg clonazepam was administered orally. One hour later, follow-up ENG was performed again to evaluate the evolution of the downbeat nystagmus. If the test was effective, then 1.0 mg clonazepam twice daily was administered to the patients.
RESULTS: Seven cases had downbeat nystagmus, including idiopathic in five, cerebellar degeneration in one, and cerebellopontine angle tumor in one. The efficacy rate for the clonazepam test was 100% in five cases of idiopathic downbeat nystagmus, whereas it was ineffective in the case of cerebellar degeneration. After long-term therapy with clonazepam, all patients with idiopathic downbeat nystagmus experienced elimination of oscillopsia, relief of diplopia, and improvement of visual acuity. Although temporary relief of downbeat nystagmus was observed 1 hour after the clonazepam test, downbeat nystagmus was not eliminated permanently.
CONCLUSION: We recommend long-term therapy by clonazepam with a dosage of 1.0 mg twice daily in cases of idiopathic downbeat nystagmus. Reducing the downbeat nystagmus as well as eliminating the oscillopsia can be anticipated.