Convergent-Divergent Nystagmus as a Manifestation of Oculopalatal Tremor

摘要

Palatal tremor is a condition that develops following a lesion causing damage to the fibre tracts within the Mollaret triangle. Palatal tremor is typically associated with a vertical pendular nystagmus. When both palatal tremor and pendular nystagmus are present in a patient, they are referred to as oculopalatal tremor. We present a patient who developed an unusual case of oculopalatal tremor months after suffering a pontine haemorrhage. The oculopalatal tremor consisted of a horizontal nystagmus demonstrating 180° phase shift coupling of between the two eyes (convergent-divergent pendular nystagmus). To our knowledge, no case of this rare type of oculopalatal tremor has been previously published. Magnetic resonance imaging revealed a central pontine lesion that extended bilaterally in our patient. In addition to damaging the central tegmentum in the pons (the main fibre tract of the Mollaret triangle), this lesion affected other anatomical structures, including the nucleus reticularis tegmenti pontis, which is located in the pons, near the paramedian pontine reticular formation. This nucleus is involved in the control of the horizontal vergence system. Thus, any change in its ability to function could lead to the emergence of convergent-divergent nystagmus. Our patient partially recovered after gabapentin treatment, exhibiting reduced nystagmus amplitude, improved visual acuity, and subjective decrease of oscillopsia.