An Update on the Effects and Complications of BoNT-A in the Management of Third, Fourth, and Sixth Nerve Palsies: A Narrative Review

Abstract

This review article explores the etiology of oculomotor palsies-including third, fourth, and sixth cranial nerve palsies-and addresses the application of botulinum toxin type A (BoNT-A) in the management of these conditions, along with its associated complications and side effects. The objective is to assess BoNT-A's potential efficacy and its role across various types of nerve palsies. A comprehensive analysis of relevant studies reveals that BoNT-A holds promise as a therapeutic option in managing these conditions. BoNT-A injection into the lateral rectus muscle proves to be an effective treatment for addressing post-traumatic third nerve palsy. This is achieved by providing symptom relief and diminishing the necessity for subsequent surgical interventions. In the context of fourth nerve palsy, BoNT-A injection into the inferior oblique or inferior rectus muscles presents potential benefits but is accompanied by certain limitations. Additionally, previous studies have shown that BoNT-A injection into the antagonist medial rectus muscle for treatment of sixth nerve palsy results in favorable outcomes, such as contributing to functional improvement. The literature highlights the importance of timing, dosage, and grade of muscle dysfunction when administering BoNT-A injections. BoNT-A injection is an effective option to manage different types of cranial nerve palsies and improve binocular function. Furthermore, it plays an integral role in preventing antagonist muscle contracture and, hence, the need for future surgical intervention.

Keywords: Cranial Nerve; Motor Nerve Palsy; Botulinum Toxin Type A.

Figure 1

A 32-year-old woman presented with right lateral rectus palsy and –4 abduction limitation (a–c). The patient experienced ptosis, exotropia, and adduction limitation 4 days following BoNT injection into the right medial rectus muscle (d–f). She achieved complete resolution of all symptoms one month after BoNT injection (g–i).^[63].