The efficacy of botulinum neurotoxin A for the treatment of complete and partially recovered chronic sixth nerve palsy.

Esotropia from chronic sixth nerve palsy or paresis usually requires surgery. Chemodenervation of the antagonist medial rectus muscle, while popular for the treatment of acute sixth nerve palsies and pareses, has not been used extensively for chronic cases. In this study, 22 patients with sixth nerve palsies or partially recovered palsies of greater than 5 months duration were treated with chemodenervation. The etiologies of the sixth nerve palsies were trauma (n = 7), tumor (n = 4), infection/inflammation (n = 3), nerve compression from aneurysm or increased intracranial pressure (n = 4), congenital (n = 1), ischemia (n = 2), and idiopathic (n = 1). The mean preinjection deviation was 41 prism diopters. A total of 38 injections were administered (mean, 1.7 per patient). Each patient received an injection of 2.5 to 7.5 units (mean, 4.1) of botulinum neurotoxin A to the ipsilateral medial rectus muscle. Treatment success was assessed 6 months after the last injection. A course of chemodenervation significantly improved the alignment of 9 of the 22 patients (41%). The mean postinjection deviation was 8 delta. Seven patients (32%) had single binocular vision in primary position restored. These patients had a mean horizontal binocular field of 70 degrees (range, 40 degrees to 100 degrees). Thirteen patients (59%) had only modest improvement and required surgery. The data suggest that injection of botulinum neurotoxin A is a useful treatment for some patients with chronic sixth nerve weakness. A course of chemodenervation therapy compares less favorably with transposition surgery with concomitant neurotoxin injection for the treatment of these difficult problems.