Acquired Synergistic Divergence: Contrary to Current Literature.

Current literature reports synergistic divergence as a rare, congenital ocular motility pattern associated with adduction palsy. Its mechanism has been likened to Duane's syndrome, and some suggest it be referred to as Duane's Type 4 (Gupta et al. 2010; Schliesser et al. 2016; Wilcox et al. 1981; Khan et al. 2016). There are no published reports of synergistic divergence as an acquired condition, making this case report seemingly the first of its kind. This case report describes an 18-year-old female who presented to clinic in 2013 with symptoms of diplopia and left eye turning outwards. Orthoptic assessment and MRI confirmed a third nerve palsy secondary to cavernous sinus schwannoma. Further monitoring showed progression of the cranial nerve palsy but a stable schwannoma and no aberrant regeneration noted in five years of follow up. The patient was treated with multiple botulinum toxin injections and had squint correction surgery in 2017. Seven months later, synergistic divergence was first noted and remained stable in all following assessments. While the aetiology of acquired synergistic divergence in this case is unclear, we can be confident it is unlikely to be of congenital origin as it was not noted until adulthood and after five years of investigations. This report will discuss possible aetiologies of acquired synergistic divergence and, contrary to current literature, suggest clinicians should consider the possibility that synergistic divergence can be acquired, though is likely to be even rarer than its congenital form.