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Acute‐onset esotropia (ET) is a rare presentation of Chiari I malformation. The ET may resolve following neurosurgical decompression, although this is not usually immediate.1 Where neurosurgery is not undertaken, Kowal et al2 suggest prismatic correction or strabismus surgery. The latter may result in temporary correction of the strabismus, as the strabismus can recur and resolves only following decompression.3 Botulinum toxin (BT) has been reported as successful in one case where the ET did not resolve following neurosurgery.4 Despite BT being a common treatment for acute acquired concomitant ET,5 no previous case has been reported in which BT was used prior to neurosurgical decompression for Chiari I malformation.
A 16‐year‐old girl experienced diplopia during swimming, and presented to the A&E Department on the day of onset. She gave a history of occasional, brief diplopia. On examination, there was 16Δ ET at near and 20Δ ET at distance. The angle of deviation reduced on versions. Saccade to the right was possibly hypometric; no nystagmus was present. Over 2 weeks, the angle increased to 40Δ ET, saccades to the right became definitely hypometric and abducting nystagmus developed. MRI scan revealed Chiari I malformation with tonsillar descent to about 12 mm below the foramen magnum, with loss of cerebrospinal fluid (CSF) spaces indicating impaction of neural tissue (fig 11).). Neurosurgery was discussed, but delayed for 8 months.
Three months after onset, the angle had increased to 45Δ ET at near and distance. Four units of BTA were injected into the right medial rectus muscle with electromyographic guidance under topical anaesthesia. Initially there was an overcorrection (12ΔXT, 5ΔRHT, with –3½ limitation right adduction). Following recovery of medial rectus function, 6Δ exophoria at near and 4Δ esophoria at distance were present. Eight months following BT injection there had been no recurrence of strabismus and the patient underwent neurosurgical decompression. Currently the patient is orthophoric and shows hypometric saccades to the right and left, and fine pendular‐like nystagmus on right and left gaze.
BT restored binocular single vision (BSV) in a patient awaiting neurosurgical decompression for Chiari I malformation. Neurosurgery was delayed to fit in with the patient's education. BT was used in the expectation that repeat injections would be necessary as the aetiological cause had not been treated at this time. Following the BT, BSV was maintained for 8 months prior to decompression surgery. Recurrence of ET following strabismus surgery has occurred over a variety of time frames upwards from 3 months following strabismus surgery.6
Surgical decompression improves ocular manifestations such as nystagmus, but this may not be for several months.7 In our case, nystagmus and hypometria had not resolved 3 months following surgery.
BT should be considered as a treatment option to restore alignment in acute‐onset ET due to Chiari I malformation. Further case series are required to determine the effectiveness of BT compared with strabismus surgery.
Competing interests: None declared.