Acquired Esotropia in Cerebellar Disease: A Case Series Illustrating Misdiagnosis as Isolated Lateral Rectus Paresis and Progression Over Time

We highlight an under-recognised cause of acquired esotropia with this prospective observational case series of adults with diplopia secondary to cerebellar dysfunction. We also show deterioration of cerebellar esotropia over time, which has not been previously described. Seven adults (four women) developed diplopia at a median age of 63 years (range: 31-75 years), as the initial manifestation of the underlying cerebellar disorder. Causes of cerebellar dysfunction were familial cerebellar ataxia of unknown mutation (two patients), idiopathic cerebellar ataxia (four patients), and spinocerebellar ataxia 3 (one patient). At onset, three patients had unilateral and four had bilateral lateral rectus under-action. These were initially diagnosed as lateral rectus paresis, but the diagnosis was revised, as our examination showed no slowing of abducting saccades assessed clinically and full abduction with gaze-evoked nystagmus. Esotropia was concomitant and worse for distance, although at onset one patient's esotropia was equal for near and distance. There was a trend of worsening esotropia over time, following a median interval follow-up of 4 years (range: 1-18). All patients were first observed to have cerebellar eye signs after a median interval of 5 years (range: 1-30) from presentation, i.e., impaired pursuit (7/7 patients), gaze-evoked nystagmus (7/7), hypometric saccades (3/7), downbeat nystagmus (2/7), and skew deviation (4/7). Only two patients have not developed non-ocular cerebellar eye signs, after 5 and 8 years from diplopia onset, respectively; the other five patients had gait ataxia, which could be mild. The patients were successfully treated with prisms (7/7), botulinum toxin injections (1/7), and strabismus surgery (1/7).