Urinary incontinence is a common adverse effect of spaying and is reported in 20% of spayed dogs (1). The cause is acquired incompetence of the urethral closure caused by spaying, called urethral sphincter mechanism incompetence USMI (2). The pathophysiologic mechanism leading to reduced urethral closure after spaying is still unknown.

According to the pathophysiology the medical and surgical treatments aim at improving the urethral closure. Alpha-adrenergic agonists such as phenylpropanolamine or ephedrine hydrochloride are treatments of choice for USMI. If medical treatment is unsatisfactory, or the effect diminishes over time, surgical procedures such as colposuspension (3), urethropexy (4) or endoscopic injection of collagen into the submucosa of the proximal portion of the urethra (5) may be used.

The endoscopic injection of collagen has been described (5). Via general anesthesia, the dogs are positioned in dorsal recumbency with the hind limbs extended cranially. A human cystoscope (Karl Storz GmbH & Co. KG, 78532 Tuttlingen, Germany; KARL STORZ Veterinary Endoscopy, Goleta, CA 93117) is passed into the urethra via the external orifice. Approximately 1.5 cm caudal to the neck of the bladder, 3 injections of collagen (Zyplast, Inamed, Santa Barbara, 93111 California, USA) are made into the urethral submucosa at 2:00, 6:00, and 10:00 o'clock positions. The deposits bulge into the urethral lumen and improve urethral closure at the site of the injections. The procedure is considered complete when, on viewing through the cystoscope, the urethral lumen is closed by the collagen deposits.

A retrospective study was recently performed to evaluate the long-term success of endoscopic injection of collagen as a treatment for USMI in 40 female dogs (6). Endoscopy was used for diagnosis and treatment with 3 urethral submucosal injections of collagen in the proximal portion of the urethra. In 5 dogs, it was not possible to pass the cystoscope into the urethra via the external orifice. Therefore, a laparotomy and cystotomy were performed for placement of the collagen. Dogs that had recurrence of urinary incontinence after surgery were either treated with phenylpropanolamine (1.5 mg/kg, q 8 h, Incontex, Dr. Gräub AG, 3018 Bern, Switzerland; Proin, PRN Pharmacal, Pensacola, FL 32514) or ephedrine hydrochloride (1.0 mg/kg, q 12 h, Caniphedrin, G. Streuli & Co. AG, 8730 Uznach, Switzerland) orally at the recommended dose or underwent a second collagen injection procedure.

With a follow-up period of 9 to 78 months (mean, 33 months), 27 (68%) dogs were continent for 1 to 64 months (mean, 17 months) after treatment. In 10 dogs, incontinence improved, and in 6 dogs, continence was achieved for 9 to 47 months (mean, 23 months) with additional treatment with alpha-adrenergic drugs. In 3 dogs, incontinence was unchanged.

As long as 12 months after treatment, there was a progressive deterioration in the results in 16 dogs, after which their condition stabilized (see table). Flattening of the deposits, rather than resorption, was likely the cause of reoccurrence of incontinence. Mild and transient adverse effects developed in 6 (15%) dogs. Long-term success was satisfactory. In most dogs, the final result was evident within the first 12 months after treatment.

The success rate in dogs was similar to that of polytef paste (7), but in contrast to polytef no foreign body reactions were observed after collagen injections. In dogs in which there is only a partial response to the collagen injection, continence may be achieved by additional use of phenylpropanolamine, ephedrine hydrochloride, or both, although these were ineffective before the injection. It appears that even in treatment-resistant cases, sympathomimetic substances have an effect on smooth muscle fibers of the urethra, which is not clinically apparent without the presence of collagen deposits.

The incidence of complications was 15%, which is comparable to that of women (8). However, in dogs the complications were mild and of short duration. Urinary retention is a dreaded complication and develops in from 1.9% to 18% of treated women (8, 9). In the present study this complication was not observed.

Collagen injection compares well to established surgical methods for treatment of canine USMI. After urethropexy, 56% of affected dogs were continent and 27% had improvement of incontinence (4). A similar success rate was observed after colposuspension, with 53% of the female dogs continent and 38% with marked improvement (10).

Collagen injection into the submucosa of the proximal portion of the urethra is a suitable method for treatment of urethral sphincter incompetence in female dogs because of the good success rate, minimally invasive nature of the procedure, and the risk of adverse effects. However, the initial result may deteriorate up to 12 months after the procedure and administration of alpha-adrenergic substances or re-treatment may be necessary.

Success rate of collagen injection in 40 bitches.

* At the time of death or end of the study
** were euthanized 3 months after injection

References

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2.  Rosin AE, Barsanti JA. Diagnosis of urinary incontinence in dogs: Role of the urethral pressure profile. J Am Vet Med Assoc. 1981; 178: 814-822.

3.  Holt PE. Urinary incontinence in the bitch due to sphincter mechanism incompetence: surgical treatment. J Small Anim Pract. 1985; 26: 237-246.

4.  White RN. Urethropexy for the management of urethral sphincter mechanism incompetence in the bitch. J Small Anim Pract. 2001; 42: 481-486.

5.  Arnold S, Hubler M, Lott-Stolz G, et al. Treatment of urinary incontinence in bitches by endoscopic injection of glutaraldehyde cross-linked collagen. J Small Anim Pract. 1996; 37: 163-168.

6.  Barth A, Reichler IM, Hubler M, Haessig M, Arnold S. Evaluation of long-term effects of endoscopic injection of collagen into the urethral submucosa for treatment of urethral sphincter incompetence in female dogs: 40 cases (1993-2000). JAVMA. 2005; 226: 73-76.

7.  Arnold S, Jäger P, Di Bartola SP, et al. Treatment of urinary incontinence in dogs by endoscopic injection of Teflon. J Am Vet Med Assoc. 1989; 195: 1369-1374.

8.  Stothers L, Goldenberg SL, Leone LF. Complications of periurethral collagen injection for stress urinary incontinence. J Urol. 1998; 159: 806-807.

9.  Gorton E, Stanton S, Monga A, et al. Periurethral collagen injection: a long-term follow-up study. BJU Int. 1999; 84: 966-971.

10. Holt PE. Long-term evaluation of colposuspension in the treatment of urinary incontinence due to incompetence of the urethral sphincter mechanism in the bitch. Vet Rec. 1990; 127: 537-542.