Intravesical botulinum toxin injection is commonly performed under local anaesthesia for refractory overactive bladder and bladder pain syndromes. Procedural discomfort remains a key limitation, particularly in office-based settings. Bladder distension may influence nociceptive activation and urgency, yet the impact of bladder filling status on procedural pain has not been systematically evaluated in routine clinical practice.

To determine whether lower bladder filling reduces procedural pain, and to model the continuous association between bladder volume and clinically relevant symptom burden

prospective cohort, 112 consecutive adults undergoing intravesical onabotulinumtoxinA injection under local anaesthesia were studied. Bladder volume at the start of injection was recorded as a continuous exposure and also analysed in prespecified low-volume (100-150 mL; n=56) and high-volume (250-350 mL; n=56) groups. The primary endpoint was immediate post-procedural pain on a 10-point visual analogue scale. Secondary endpoints were high pain (VAS at least 5), immediate urgency/LUTS flare, procedure duration, and completion. Multivariable linear and logistic regression adjusted for age, sex, diagnosis, first versus repeat treatment, injection number, and baseline LUTS burden.

Across the full cohort (n=112), higher bladder volume was independently associated with greater pain (adjusted beta 0.54 VAS points per 50 mL increase, 95% CI 0.45 to 0.63, p<0.001). Patients in the high-volume group had higher mean pain scores than the low-volume group (4.8 +/- 0.9 vs 2.9 +/- 1.0; mean difference 1.90, 95% CI 1.52 to 2.29, p<0.001).

Each 50 mL volume increase was associated with higher odds of clinically important pain (adjusted OR 4.47, 95% CI 2.17 to 9.21, p<0.001) and immediate urgency/LUTS flare (adjusted OR 2.10, 95% CI 1.55 to 2.86, p<0.001). First treatment and IC/BPS were additional independent predictors of higher pain, whereas procedure duration remained similar across volume strata.

Lower bladder filling appears to improve tolerability during intravesical botulinum toxin injection without compromising procedural efficiency. Modelling bladder volume as a continuous exposure, rather than a simple binary comparison, strengthens the biological signal and supports prospective protocol optimisation in office-based Botox pathways.

Continence 19S (2026) 102483
DOI: 10.1016/j.cont.2026.102483