An evaluation of 30 years’ experience in the use of botulinum toxin injections in the management of sixth nerve palsies

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ABSTRACT Intrroduction Sixth nerve palsy is the most common type of extraocular muscle palsy. The therapy options in sixth nerve palsies include monitoring with or without conservative treatment, botulinum toxin injections or strabismus surgery. The aim of this retrospective study was to compare botulinum toxin (BT) injections into the medial rectus to conservative treatment in sixth nerve palsies. The rate of patients improved after intervention and treatment outcomes for the two treatment options were be evaluated at a German tertiary referral center. Methods A service evaluation was conducted on adult patients with sixth nerve palsy. Patient files were reviewed and data including abduction deficit and size of deviation were collected retrospectively. Patients which presented between January 1987 and April 2022 were considered. Patients were allocated into two treatment groups: BT injected into medial rectus or conservative treatment, which included observation, providing occlusion and Fresnel prisms. Inclusion criteria were attendance of two visits with orthoptic assessment. Exclusion criteria included presence of further oculomotor palsies, strabismus, strabismus surgery and suppression. Non-parametric statistical analysis was conducted using IBM® SPSS Statistics. Results A total of 606 adult patients with unilateral or bilateral sixth nerve palsy attended during the named period. A total of 137 adult patients met the inclusion criteria. Of which, 36 had a bilateral palsy, 101 had a unilateral palsy. 45.26% (n = 62) were treated with BT injections and 54.75% (n = 75) were treated conservatively. The median initial abduction deficit was greater in the BT group, (−4 to −5 after Scott and Kraft) than in the conservative treatment group (−1). The initial angle of deviation at distance was significantly larger in the BT group than in the conservative treatment group (p = <0.001). The rate of improvement in the BT group was 24.19% (n = 15) and 20% (n = 15) in the conservative treatment group. When excluding longstanding palsies rates of improvement in both groups increased to 28.85%. The improvement of the angle of deviation at distance in all patients was greater in the BT group (p = <.001). The improvement of abduction in bilateral palsies were greater in the BT group (p = .016), but in unilateral palsies, there was no significant difference in abduction improvement in the two treatment groups (OD p = .3, OS p = .406). Conclusion This service evaluation found that BT injection into medial rectus in unilateral and bilateral sixth nerve palsies did not increase the rate of improvement compared to conservative treatment. But BT injections reduced the angle of deviation to a greater extent than conservative treatment. Additionally, BT was able to improve abduction in bilateral palsies to a greater extent than conservative treatment. It is recommended a BT injection is considered in symptomatic bilateral sixth nerve palsies to enable fixation and improved ocular motility. More research is needed to verify reliable clinical guidelines for the use of BT in sixth nerve palsies.