Gabapentin and memantine increases randomness of oscillatory waveform in ocular palatal tremor

A 6-month trial of memantine for nystagmus and associated phenomena in oculopalatal tremor

“…Such factors might include memantine's “unwanted” effect on the PN waveform randomness (i.e., increase in waveform shape heterogeneity), coexisting ocular motor deficits also impairing vision (e.g., internuclear ophthalmoplegia, gaze palsies, vestibular deficits, etc. ), and/or the presence of distinct/opposite effects of memantine on OPT-related nystagmus planes (i.e., horizontal, vertical and/or torsional) as shown in the present study ( 5 , 7 , 8 ). In addition, it must also be stressed that while NEI-VFQ-25 has been used before to evaluate OPT patients, this tool has not been specifically designed to assess the functional consequences of nystagmus ( 5 ).…”

“…Whether such selective effect of memantine on fibers carrying signals for horizontal eye movements could be dosage-dependent, i.e., particularly seen when using lower dosages of memantine is highly speculative and lacks clinical and experimental evidence. Another non-mutually exclusive explanation for distinct/opposite responses to memantine depending on nystagmus plane is an increase in the nystagmus waveform randomness (i.e., nystagmus waveform shape from trial to trial) after memantine use, which might influence final/mean nystagmus velocity/amplitude waveform in different planes ( 8 ). Importantly, one cannot exclude that, particularly in patients with mild nystagmus, the aforementioned changes in nystagmus over time might reflect natural fluctuations.…”

“…Given the previously reported disparity between amplitude reduction of the dominant plane of PN and the relatively mild or unpredictable subjective visual improvement in OPT patients, in this work, we asked if there are distinctive effects of memantine on horizontal and vertical components of nystagmus (including PN, and associated jerk nystagmus, if present) in individual patients, which could also help to explain the idiosyncratic subjective visual response seen in OPT ( 8 ). In addition, as data are sparse regarding long-term outcomes for memantine response in OPT, we evaluated the effect of memantine 20 mg per day in OPT patients during a 6-month period, focusing on several aspects of the outcome, including nystagmus intensity in each plane, visual acuity, SVV, PT and facial movements frequency, and quality of life measurements.…”

“…There is anecdotal data showing that memantine, an N-methyl- D -aspartate (NMDA) receptor antagonist, might reduce PN amplitude, velocity and frequency variability, and improve visual acuity and distance oscillopsia in some but not all patients with OPT-related PN ( 5 – 7 ). An additional increase in PN waveform randomness (i.e., waveform heterogeneity and visible differences in their shapes) may account for the idiosyncratic subjective visual response, often not correlating with an objective reduction of PN ( 6 , 8 ). Jerk nystagmus has also been shown to improve with memantine ( 6 ).…”

“…Jerk nystagmus has also been shown to improve with memantine ( 6 ). Importantly, all the above studies were small (4–6 OPT patients), with a short follow-up (15–21 days), frequently using memantine 40 mg per day, and usually only providing data from the dominant plane of PN (i.e., the plane [horizontal, vertical, or torsional] with the more regular and/or the largest amplitude of eye oscillation in each eye) as an outcome for therapeutic response ( 5 – 8 ). Almost all patients in the above series had at least one side effect while taking memantine 40 mg per day, including lethargy, drowsiness, maniac episode/confusional state, increased emotionality, irritability and anxiety, ataxia, and neuropathic pain ( 5 – 8 ).…”