Background and Purpose: This study was undertaken to examine vestibulo-ocular
reflex
(VOR) characteristics in myotonic dystrophy type 1 (DM1) and type 2 (DM2) using video
head impulse testing (vHIT).
Methods: VOR gain, refixation saccade prevalence, first saccade amplitude, onset latency,
peak velocity, and duration were compared in DM1, DM2, age-matched
normal
controls, and patients with peripheral and central vestibulopathies.
Results: Fifty percent of DM1 and 37.5% of DM2 patients demonstrated reduced VOR
gain. Refixation saccade prevalence for horizontal canal (HC) and posterior canal (PC) was
significantly higher in DM1 (101 ± 42%, 82 ± 47%) and DM2 (70 ± 45%, 61 ± 38%) compared
to controls (40 ± 28% and 43 ± 33%, p < 0.05). The first saccade amplitudes and
peak velocities were higher in HC and PC planes in DM1 and DM2 compared to controls
(p < 0.05). HC slow phase eye velocity profiles in DM1 showed delayed peaks. The asymmetry
ratio, which represents the percentage difference between the first and second
halves of the slow phase eye velocity response, was therefore negative (−22.5 ± 17%,
−2.3 ± 16%, and − 4.7 ± 8% in DM1, DM2, and controls). HC VOR gains were lower and
gain asymmetry ratio was larger and negative in patients with DM1 with moderate to severe
ptosis and a history of imbalance and falls compared to the remaining DM1 patients
(p < 0.05). In peripheral vestibulopathies, saccade amplitude was larger, peak velocity was
higher, and onset latency was shorter (p < 0.05) than in DM1. In central vestibulopathy
(posterior circulation strokes), saccade peak velocity was higher, but amplitude and onset
latency were not significantly different from DM1.
Conclusions: VOR impairment is common in DM1 and DM2. In DM1, refixation saccade
characteristics are closer to central than peripheral vestibulopathies. Delayed peaks in the
vHIT eye velocity profile observed in patients with DM1 may reflect extraocular muscle
weakness. VOR impairment and VOR asymmetry in DM1 are associated with imbalance
and falls.
