Patterns of ocular oscillation in oculopalatal tremor - Imaging correlations

Objective: To determine patterns of nystagmus in oculopalatal tremor (OPT, also designated oculopalatal myoclonus) and correlate them with MRI changes in the inferior olivary nuclei (ION). Mixed torsional-vertical pendular nystagmus (PN) in OPT has been considered to signify unilateral brainstem damage and symmetric vertical nystagmus considered to indicate bilateral disease. Methods: Ocular oscillations were analyzed in 22 patients with OPT, 20 from focal brainstem lesions, with or without cerebellar lesions, and two from the progressive ataxia and palatal tremor syndrome. MRI was performed in all patients. Results: Patients had mainly vertical oscillations with varied combinations of torsional and horizontal components. Fourteen patients had binocular symmetry of PN and eight showed dissociated PN. MRI demonstrated ION signal change, unilateral in 14 and bilateral in eight. Unilateral olivary changes were associated with symmetric PN in six and with dissociated nystagmus in eight patients. Bilateral olivary changes were visible in eight patients with symmetric nystagmus. Dissociated PN was associated with MR pseudohypertrophy of ION on the side of the eye with greater vertical amplitude of oscillation. Notably, four patients never developed palatal tremor despite ION signal change. OPT resolved in one patient after 20 years and was markedly reduced in another patients after 6 years. Conclusions: Dissociated pendular nystagmus predicted asymmetric (unilateral) inferior olivary pseudohypertrophy on MRI with accuracy, but symmetric pendular nystagmus was associated with either unilateral or bilateral signal changes in the inferior olivary nucleus. Instability of eye velocity to position integration from damage to the paramedian tract projections and denervation of the dorsal cap of the inferior olive are proposed mechanisms of the pendular nystagmus.