Video 4.7 Slow ipsiversive horizontal saccades in a brainstem syndrome due to paramedian pontine reticular formation (PPRF) involvement from Neuro-Ophthalmology and Neuro-Otology Textbook

: This is a 60-year-old man who presented for imbalance and oscillopsia 10 months after surgery and 8 months after radiation for Merkel cell carcinoma of the neck. He developed imbalance after surgery and diplopia and oscillopsia 6 months prior to our evaluation. MRI showed enhancement of both 6th nerves, as well as the left 9th, 10th, 11th and ascending portions of the 12th cranial nerve. There was a mild left lower motor neuron facial palsy as well. Exam demonstrated mild right adduction and bilateral abduction deficits, without clear evidence of a right partial 3rd nerve palsy otherwise. Convergence was relatively spared compared to adduction OD. Saccades to the left were very slow, seemingly out of proportion to his mild motility deficits. Pursuit appeared normal vertically and horizontally. There was a right hypertropia due to a skew deviation with a left head tilt, and ocular counterroll with top poles deviated toward the left ear (i.e., a leftward ocular tilt reaction). There was very mild vertical-torsionalpendular nystagmus OS>OD, seen best with the ophthalmoscope (unable to appreciate in this video because it was so subtle). ; To an optokinetic stimulus moved to the right, there were no leftward fast phases. With head impulse testing to the left, there was were abnormal catch-up saccades suggesting unilateral vestibular loss on the left. Given the fact that leftward saccades were so slow, with head impulses to the right, leftward movements were very normal appearing -if slow leftward saccades were due to nuclear(left 6th nucleus)/infranuclear motility deficits, leftward movements with the vestibulo-ocular reflex (VOR) should look just as slow. In this case, the VOR resulted in much faster movements, which strongly suggests a supranuclear mechanism (in addition to the fact that his right adduction deficit improved with convergence); therefore, it was felt that the left paramedian pontine reticular formation (PPRF) had been preferentially affected as well. Additionally, there was no impairment of smooth pursuit to the left. A left dorsal pontine localization was also supported by pendular nystagmus that had the appearance of oculopalatal tremor, which is commonly related to pathology in the vicinity of the descending central tegmental tract in the pons (in his case without palatal tremor or inferior olivary hypertrophy on MRI -perhaps full-blown ‘oculopalatal tremor' was evolving), and a left lower motor neuron (LMN) facial palsy, which if ‘central', would also support a left pontine localization. However, in his case, a left peripheral LMN facial palsy was entirely possible. The skew deviation (right hypertropia) could theoretically relate to damage just caudal to the decussation involving the utricule-ocular motor fibers at the left pontomedullary junction, although since his disease was so multi-focal and given otherwise unremarkable imaging of the cerebellum and brainstem, it was difficult to localize all of his deficits. - - : This is a patient with a complicated brainstem syndrome that developed following head and neck cancer diagnosis (status post surgery and radiation), that included left (lower motor neuron) 7th and 8th nerve palsies, in addition to slow saccades to the left with normal saccades in other directions. With an optokinetic stimulus moved to the right, there were no leftward fast phases. Leftward eye movements with pursuit and the head impulse test to the right (the vestibulo-ocular reflex is responsible for conjugate eye movements to the left) appeared to be of normal speed. This constellation of findings (i.e., normal pursuit and VOR, abnormal saccades) argued for a left PPRF lesion and against a left 6th nuclear lesion, although MRI did not demonstrate a discrete pontine lesion. (Video and legend created with the assistance of Dr. Tony Brune) https://collections.lib.utah.edu/ark:/87278/ s6n058z