Are most sixth nerve palsies really paralytic?

Etiology and date of palsy are two important parameters that affect the treatment protocol of sixth nerve palsies. This study evaluated the treatment protocols and outcomes of treatment in sixth nerve palsies.

Thirty-four patients who had sixth nerve palsy were included. Botulinum toxin A (BTX) injection was performed on patients with acute sixth nerve palsy and paresis (BTX group), whereas chronic cases received only horizontal surgery (surgery group). All patients in the BTX group received a BTX injection into the ipsilateral medial rectus muscle. Patients in the surgery group underwent either ipsilateral medial rectus recession or recession combined with lateral rectus resection without the transposition procedure.

Fifteen patients were treated with a BTX injection to the medial rectus muscle. One patient underwent ipsilateral medial rectus muscle recession and 6 patients received both medial rectus recession and lateral rectus resection in the same session. Measurement of esotropia was 24.9 prism diopters (PD) (range: 18 to 35 PD) before treatment in the BTX group. The recovery rate was 86.6% (13 of 15) without any residual deviation. In the surgery group, the mean preoperative deviation was 35.1 PD (range: 14 to 75 PD), which decreased to mean 2.57 PD (range: 0 to 10 PD) postoperatively. The achievement of orthotropia rate was 85.7%.

BTX injection was found to be an effective treatment because it prevented medial rectus contraction in acute sixth nerve palsies. Correction of deviation with the recession of contracted medial rectus muscles and resection of lateral rectus muscles without the need of transposition in chronic sixth nerve palsy testified that most sixth nerve palsies involve partial paralysis rather than complete paralysis.