Square wave oscillations in Parkinsonism

This patient presented with complaints of imbalance, and had signs of Parkinsonism on examination (i.e., bradykinesia, postural instability, rigidity). While there were no clear ocular motor or neuroimaging signs to suggest progressive supranuclear palsy (e.g., vertical saccadic or gaze palsy) or multiple system atrophy (e.g., downbeat, gaze-evoked nystagmus, saccadic dysmetria), there were frequent asymptomatic square wave jerks (with an inter-saccadic interval) on his examination, which at times were continuous and consistent with square wave oscillations (SWO). Oscillations such as SWO and macrosaccadic oscillations (which are larger, straddle fixation, and are due to cerebellar disease with associated saccadic hypermetria) may exist on a continuum, with some patients displaying more than one intrusion or oscillation during a single visit. Or, a patient with resolving ocular flutter (where there is no inter-saccadic interval) may transition to another intrusion/oscillation as they recover.