Evaluation of nanofibrillated cellulose as a urethral bulking agent in female dogs with acquired urethral sphincter mechanism incompetence: a prospective clinical study.

Urethral bulking agent (UBA) implantation is a minimally invasive, effective and safe alternative treatment for refractory urethral sphincter mechanism incompetence (USMI). However, repeated implantations are frequently needed to maintain continence. Therefore, a prospective interventional clinical study with eight client-owned neutered female dogs was designed to evaluate the clinical efficacy and 12-month outcome of nanofibrillated cellulose (NFC), a novel biomaterial as a UBA. Concurrent causes of urinary incontinence were excluded with clinical and neurological assessment, blood and urine sampling, magnetic resonance imaging (MRI), retrograde vaginourethrography, cystoscopy, and urodynamic testing. A continence score (CS) was assigned before and after treatment, and monthly thereafter. Furthermore, the dogs were followed with MRI, retrograde vaginouretrography, and urethroscopy at 1 and 12 months or at the time of euthanasia or recurrence. All dogs were continent (CS ≥ 8/10) at 1 month with a significant increase in mean CS (p < 0.0001, difference 5.4, 95% CI 4.1-6.6). Median duration of continence was 8 months (IQR 4 - not estimable). At 12 months, the treatment response was still significant (p = 0.0010) with (n=4/7) or without (n=3/7) medical intervention. The imaging and urethroscopy findings suggest that flattening of the deposits with or without mucosal ulceration may contribute to recurrence. Sporadic bacterial cystitis was diagnosed in two dogs and recurrent cystitis in one. In conclusion, NFC showed promising short-term effect and a low complication rate when used as a UBA. Urinary incontinence resolved after single NFC implantation in all dogs for a median of 8 months without adjunctive treatment.