Clinical presentation of pseudo-abducens palsy

Pseudo-abducens palsy is a neurologic limitation in abduction with an intact abducens nerve. This rare condition can be observed when voluntary eye movements show impairment in lateral gaze, yet the vestibulo-ocular reflex (VOR) demonstrates full abduction. The intact VOR indicates the integrity of the infranuclear abducens nerve, thus suggesting that a pseudo-abducens palsy is likely caused by supranuclear pathology.

A 63-year-old African American man presented with sudden-onset, binocular, horizontal diplopia. Extraocular motilities revealed a complete restriction of abduction OS on pursuits with intermittent spasm of the right medial rectus that was most evident in primary and left gazes. No cyclodeviation or vertical deviation was found. Doll's head maneuver was used to stimulate the VOR, which facilitated complete abduction OS, despite its gross limitation on pursuits. The intact VOR and impaired abduction on pursuits, coupled with contralateral esotropia, yielded a diagnosis of pseudo-abducens palsy.

Although considered to be a rare condition, it is important for the clinician to differentiate pseudo-abducens palsy from a classic abducens infranuclear palsy. Presented is a case displaying the typical features of a pseudo-abducens palsy, in conjunction with contralateral esotropia, which further supports the theory of a dysfunctional supranuclear vergence pathway.