Anticholinergics form the first-line treatment for the neurogenic detrusor overactivity (NDO) in SCI patients. However majority of patients do not achieve satisfactory outcome with the standard dose therapy. Further treatment strategy includes increasing the dose of or using combination of anticholinergics up to the best tolerable doses (1). Intravesical botulinumtoxinA injection has been the regulator approved second line treatment option in SCI patients with suboptimal response to anticholinergics (2). 
However, with the recent availability of mirabegron, it has become another option frequently added to the anticholinergic regimen, with the potential summation of their beneficial effects on the bladder(3). Given its ease of administration and low cost, the oral combination regimen of mirabegron and anticholinergic has the potential to be the preferred choice ahead of injectable botulinum therapy. However it is still not clear if the oral combination treatment including the mirabegron provides satisfactory control of NDO at par with botulinumtoxinA in these patients.

We retrospectively reviewed the records of 30 SCI patients, who had earlier been referred from other institutions to our department for doing their urodynamic study. From their treatment charts we separated patients into two groups. Fifteen SCI patients who had anticholinergic refractory NDO and were given add-on mirabegron, at 25 mg per day, and were continuously on combination treatment for at least 3 months were included in group A. Another fifteen SCI patients who had received intravesical botulinumtoxinA (200units), for the management of their refractory NDO, at least 3 months earlier and not later than 6 months, were included in Group B. 
We noted their ICIQ-SF charts that were provided at the time of Urodynamic testing. We noted and compared their urodynamic findings including the ice-water test response.

Both groups of SCI patients were similar in having NDO that was refractory to the standard dose anticholinergics, with the difference of being treated along two differing lines of management.
In group A, of the 15 patients treated with the combination of mirabegron and an anticholinergic drug, six  patients (40%) were dry while another 3 patients (20%) observed more than 50% improvement after the addition of mirabegron. Urodynamics showed complete suppression of NDO in 6 patients (40%). High pressure storage, NDO with detrusor pressure more than 40 cm. and reduced compliance of less than 10 ml / cm. were noted in 9 patients (60%). Ice-water test was still positive in 10 patients (66% ) in this group.
Of the fifteen patients in group B, who had received botulinumtoxinA at least 3 months earlier, 12 patients (80%) were dry at the time of assessment. Another 2 patients noted more than 50% improvement in their symptoms after the injection treatment. Urodynamics showed complete suppression of NDO in 12 patients (80%). In another 2 patients, only low magnitude NDO (detrusor pressure <40cm.) were seen. Ice-water test became negative in 12 patients (80%) after botulinumtoxinA.

Patients in group B having received Botox for the control of refractory NDO seemed to enjoy greater degree of symptomatic improvement. Extent of urodynamic improvement was also greater and more comprehensive in terms of more complete suppression of NDO and negative ice water test in patients after botulinumtoxinA.

Initial experience suggests that more favorable response in SCI patients with refractory NDO may be obtained after botulinumtoxinA than after oral anticholinergic and mirabegron combination therapy. This was an indirect and retrospective assessment, only indicating a potential trend of efficacy of two different treatment options. However, larger prospective randomized studies are needed to clarify the issue.

Neurogenic Bladder: from Diagnosis to Management. Ellen Goldmark, Benjamin Niver, David A. Ginsberg. Current Urology Reports, 2014, Volume 15, Number 10, Page 1
Phase 3 efficacy and tolerability study of onabotulinumtoxinA for urinary incontinence from neurogenic detrusor overactivity. Ginsberg D, Gousse A, Keppenne V, Sievert KD, Thompson C, Lam W, Brin MF, Jenkins B, Haag-Molkenteller C. J Urol. 2012;187:2131–2139.
Initial experience with the treatment of neurogenic detrusor overactivity with a new ß-3 agonist (mirabegron) in patients with spinal cord injury.  Wollner J., Pannek J.  (2016)  Spinal Cord, 54  (1) , pp. 78-82.