medwireNews: Botulinum toxin (BTX) is noninferior to traditional strabismus surgery for the long-term treatment of acute acquired comitant esotropia (AACE) in children, according to the results of a North American study.
At 6 months, treatment success, defined as a total horizontal deviation of 10 prism diopters (PD) or less together with evidence of binocular single vision and no need for retreatment, occurred in significantly more patients given BTX than those who underwent surgery (89 vs 59%).
However, the primary outcome measure of the study was to assess for noninferiority at 36 months of follow-up, at which time the treatment success rates in the BTX and surgical arms were 72% and 56%, a nonsignificant difference. The lower limit of the 95% confidence interval was –5%, and therefore within the –10% predetermined threshold set to support the noninferiority of BTX to surgery.
“Our results provide, to the best of our knowledge, the longest follow-up period for patients treated with botulinum toxin for AACE,” Ryan Gise (Boston Children's Hospital, Massachusetts, USA) and co-authors write in the American Journal of Ophthalmology.
To evaluate the longer-term effectiveness of the two approaches, the team studied the outcomes of 76 children with AACE who had been treated with BTX or surgery between 2000 and 2020 at either Boston Children's Hospital or the Hospital for Sick Children in Toronto, Ontario, Canada.
The children were aged between 2 and 10 years at the onset of their esotropia and they had at least 36 months of follow-up data available after treatment. The mean age of esotropia onset was 3.4 and 3.1 years in the BTX and surgery groups, respectively, and the median preoperative distance deviation was 35 PD in both groups.
Children in the BTX group were treated with a median 5 units of onabotulinumtoxin A, which was injected into both medial rectus muscles under general anesthesia without electromyographic guidance and without conjunctival incision.
In the surgery group, the median bilateral medial rectus muscle recession was 5.0 mm, ranging from 3.5 to 6.0 mm.
Other results showed no significant differences between the BTX and surgery groups in terms of the angle of deviation (0 vs 2 PD) or stereoacuity (40 arcsecs in both groups). But compared with surgery, BTX resulted in a significantly shorter mean duration of anesthesia (6 vs 71 min), and time in the post-anesthesia care unit (40 vs 95 min).
Overall, there were no serious or permanent complications with either treatment, and no new or worsening cases of amblyopia. Common postoperative side effects of BTX included ptosis in 45% of patients “despite efforts to minimize this complication,” the researchers say, while exotropia occurred in 48% of cases, “which is unavoidable and may even be desirable,” they write. These two side effects were transient, however, and generally resolved within a median of 5–6 weeks.
“We also found that longer delay from esotropia onset to treatment was an independent risk factor for worse sensorimotor outcomes irrespective of the type of treatment,” say Gise et al.
At 6 months, the median time from esotropia onset to intervention was 3.0 months for patients with successful treatment versus 7.0 months in those with unsuccessful treatment, and the corresponding durations at 36 months were 4.0 and 6.5 months.
“We therefore recommend minimizing any delay in the treatment of these patients,” the authors say.
They conclude: “Given that botulinum toxin is also less invasive, easier to access, and has a lower cost than strabismus surgery, it remains a viable alternative in the long-term treatment of AACE in children.”
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