Organic Convergence Spasm and Nystagmus in Posterior Fossa Lymphoma

This is a 20-year-old woman, who 9 months prior to this video, first experienced episodes of vertigo and vomiting occurring when lying down or rolling over in bed. Gastrointestinal work-up was unrevealing and MRI was performed which demonstrated "multifocal nodular enhancing lesions along the ependymal surfaces of fourth, third, and lateral ventricles". She underwent biopsy of one of these lesions which led to the diagnosis of B-cell lymphoma, at which time chemotherapy was initiated. Episodes became less severe with her initial vomiting and frank vertigo symptoms transitioning to mainly a sensation of oscillopsia. At the time of this video, triggers (which were all reproduced in clinic) included rolling from right or left to center in bed; extending the head back while seated; going from seated to supine with the head/neck in an extended position or in a neutral (non-extended) position; or with prolonged supine (head/neck neutral) position, episodes spontaneously come on. During her attacks, symptoms and signs were stereotyped and consisted of convergence, miosis, and rapid high frequency nystagmus (or possibly oscillations) with horizontal and vertical components lasting for about 5 seconds or so. Oscillopsia was present each time without nausea or dizziness/vertigo. Central positional vertigo/nystagmus (commonly due to lesions around the 4th ventricle, which she has) often cause downbeat nystagmus or apogeotropic nystagmus, which was not the case in her. Activation of the near triad during these attacks (convergence and miosis) was apparent, so it is possible that the spasm could relate to midbrain pathology. Given her neuroimaging (unfortunately, unavailable for review) and specific triggers, it seemed unlikely that these episodes were functional in origin. However, psychogenic convergence spasm can have a similar appearance, and voluntary ocular flutter-like movements can also be seen with functional spasm (these are usually purely horizontal). Additionally, with the slit lamp and ophthalmoscope, she had very subtle downbeat nystagmus OD and upbeat nystagmus OS with torsional nystagmus (with the top pole of each eye beating toward the right ear). Taken together, this is most consistent with a hemi-see saw pattern of nystagmus, which can be seen with central (usually brainstem) involvement of the semicircular canal and/or utricle pathways. There was also gaze-evoked nystagmus, another sign of posterior fossa dysfunction (cerebellum or its connections) which argued against her spasms being functional.