Session: Poster session A

Is botulinum toxin injection into the inferior oblique muscle an effective surgical simulation prior to inferior oblique myectomy? A retrospective review of 69 patients

Introduction: 

A surgical simulation using botulinum toxin (BTX) injected into the inferior oblique is useful to assess for postoperative results as inferior oblique myectomy (IOM) is considered irreversible. This study aims to evaluate BTX as a surgical simulation and compare the effect of BTX injection to IOM. To the best of our knowledge this is the largest series of patients reported to have undergone both BTX and IOM.



Methods: 

The medical records of 69 patients treated with BTX into the inferior oblique muscle as a surgical simulation were reviewed. Indications and deviations before and after treatment with BTX were recorded. For those patients that underwent IOM, deviations before and after surgery were recorded. All injections were delivered using electromyographic localisation.



Results:

49 out of 69 patients had a favourable outcome and had a significant reduction in their primary deviation. Of these 49 patients; 37 underwent IOM, 5 patients are awaiting IOM, 5 patients opted for repeat BTX despite IOM being offered and 2 patients resolved.

Of the 20 patients who were deemed unsuccessful following simulation with BTX; 10 had no improvement (despite repeat treatment with a higher dose), 5 patients were lost to follow up, 2 patients died and 3 patients developed intolerable diplopia which resolved.

Comparison was made between 31 patients who underwent both BTX and IOM. 6 patients were excluded due to missing data. A successful outcome was defined as a vertical angle of deviation less than half the preoperative angle or less than 5Δ. IOM showed a higher success rate than BTX (100% vs 93.5%). No patient treated with BTX reported diplopia following IOM. 84% of patients treated with IOM were discharged following resolution of symptoms. The remaining 16% showed improvement in vertical symptoms and have proceeded to have horizontal muscle surgery.



Conclusions:

BTX to the inferior oblique muscle is a useful predictor for surgical success prior to undergoing irreversible IOM.