Professor, University of Bristol, Department of Clinical Veterinary Science, Langford, Bristol, UK
In dogs referred for the investigation of urinary incontinence, urethral sphincter mechanism incompetence (USMI) is the commonest diagnosis made in adults and is second only to ureteral ectopia in juveniles, particularly in females1.
It can present as a congenital or acquired condition. Although urethral pressure profilometry can be used to demonstrate incompetence of the urethral sphincter mechanism2, this technique is not readily available in general practice and is predisposed to a number of artefacts which can make interpretation difficult. In general practice, therefore, the diagnosis is usually made on the basis of the breed, history and by the elimination of other possible diagnoses using imaging and laboratory techniques.
This presentation will concentrate on possible treatment options.
Approximately half of bitches with the congenital form of USMI become continent following their first oestrus and so should not be neutered until they have had at least one season. Those that do not may be candidates for medical or surgical management (see acquired USMI below). Oestrogens are contra-indicated in juvenile bitches with this condition because of possible adverse 'feed-back' effects on the pituitary but alpha-adrenergics such as phenylpropanolamine could be used, pending oestrus.
Acquired USMI usually (but not always) follows spaying in the bitch3,4. It is a multi-factorial problem and a variety of factors are known or suspected to contribute to its clinical manifestation of urinary incontinence. These factors include urethral tone, urethral length, bladder neck position, body size and breed, ovariohysterectomy, hormones and obesity.
The treatment of cases of sphincter mechanism incompetence may be difficult and most therapies correct only one of the above factors. It is highly unlikely, therefore, that any one form of treatment alone will cure 100% of cases in the long-term. The response may diminish over time5 and most therapies, medical or surgical, only cure approximately 50% of affected animals in the long term.
In theory, sympathomimetic or parasympatholytic agents should improve continence control by increasing urethral tone or reducing intravesical pressure respectively but the results of clinical trials are variable and possible long-term adverse systemic effects have not been evaluated. Currently, in the UK the most popular medical treatment is the alpha-adrenergic phenylpropanolamine . Affected spayed bitches sometimes respond to oestrogen therapy but in many animals the response ceases eventually, despite increasing the dosage of oestrogens, possibly due to desensitisation of oestrogen receptors. Oestrogens sensitise the urethral smooth muscle to alpha-adrenergic stimulation and so a combination of oestrogen and alpha-adrenergic (phenylpropanolamine) therapy may be useful and reduce the dose of each individual drug, lessening the chances of side effects
The main options for surgical treatment are to attempt to:
Increase urethral resistance--e.g., peri-urethral surgical slings6,7 or artificial sphincters8; intra-urethral injection of bulking agents5,9,10;
Increase urethral length, using bladder neck reconstruction techniques11;
Re-locate the bladder neck to an intra-abdominal position by means of colposuspension12,13, urethropexy14 or, in male dogs, vas deferentopexy15,16 or prostatopexy17.
The problem with techniques intended to increase urethral resistance is that they may increase the morbidity by making an incontinent animal dysuric. Similarly, increasing urethral length carries potentially serious surgical risks and, in the reviewer's view, should be reserved for animals with severe congenital urethral hypoplasia. In the reviewer's opinion, the technique least likely to lead to serious complications is to re-locate the bladder neck to an intra-abdominal position by means of colposuspension. The greater experiences of medical urologists treating incontinent women suggests that colposuspension provides firmer anchorage of the lower urogenital tract than urethropexy and avoids urethral trauma,. However, a review of urethropexy as a treatment for urethral sphincter mechanism incompetence in 100 bitches14 revealed similar results to colposuspension although the prevalence and severity of urethral complications was higher. The author believes that cystopexy is contra-indicated in these cases since it may result in detrusor instability, a further cause of urinary incontinence!
Colposuspension is intended to move the intrapelvic bladder neck of bitches with urethral sphincter mechanism incompetence to an intra-abdominal position so that increases in intra-abdominal pressure can act simultaneously on the bladder and urethra. A long-term evaluation of cases treated by the author13 indicates that a cure-rate of 53% can be expected with most of the remaining bitches improved. Ten percent of bitches fail to respond at all to colposuspension and the complication rate is low. In male dogs, the response to medical management is poor and the results of relocation of the intrapelvic bladder neck to an intra-abdominal position 15-17 are not as good as the response to bladder neck relocation in bitches.
References
1. Holt PE, Urinary incontinence in dogs and cats. Vet Rec 1990; 127: 347-350.
2. Holt PE, 'Simultaneous' urethral pressure profilometry: comparisons between continent and incontinent bitches. J Small Anim Pract 1988; 29: 761-769.
3. Holt PE, Thrusfield MV, Association in bitches between breed, size, neutering and docking, and acquired urinary incontinence due to incompetence of the urethral sphincter mechanism. Vet Rec 1993; 133: 177-180.
4. Thrusfield MV, Muirhead RH, Holt PE, Acquired urinary incontinence in bitches: its incidence and relationship to neutering practices. J Small Anim Pract 1998; 39: 559-566.
5. Barth A, Reichler IM, Hubler M, Hassig 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). J Am Vet Med Ass 2005; 226: 73-76.
6. Muir P, Goldsmid, SE, Bellenger CR, Management of urinary incontinence in five bitches with incompetence of the urethral sphincter mechanism by colposuspension and a modified sling urethroplasty. Vet Rec 1994; 134: 38-41.
7. Nickel RF, Wiegand U, Van Den Brom WE, Evaluation of a transpelvic sling procedure with and without colposuspension for treatment of femlae dogs with refractory urethral sphincter mechanism incompetence. Vet Surg 1998; 27: 94-104.
8. Dean PW, Novotny MJ, O'Brien DP, Prosthetic sphincter for urinary incontinence: results in three cases. J Am Anim Hosp Ass 1989; 25: 447-454.
9. Arnold S, Jager, P, Dibartola SP, Lott-STolz G, Hauser B, Hubler M, Fairburn A, Rusch P, Treatment of urinary incontinence in dogs by endoscopic injection of Teflon. J Am Vet Med Ass 1989; 195: 1369-1374.
10. Arnold S, Hubler M, Lott-Stolz G, Rusch P, Treatment of urinary incontinence in bitches by endoscopic injection of glutaraldehyde cross-linked collagen. J Small Anim Pract 1996; 37: 163-168.
11. Holt PE, Surgical management of congenital urethral sphincter mechanism incompetence in eight female cats and a bitch. Vet Surg 1993; 22: 98-104.
12. Holt PE, Urinary incontinence in the bitch due to sphincter mechanism incompetence: surgical treatment. J Small Anim Pract 1985; 26: 237-246.
13. 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.
14. White RN, Urethropexy for the management of urethral sphincter mechanism incompetence in the bitch. J Small Anim Pract 2001; 42: 481-486.
15. Weber UT., Arnold S, Hubler, M & Kupper, JR, Surgical treatment of male dogs with urinary incontinence due to urethral sphincter mechanism incompetence. Vet Surg 1997; 26: 51-56.
16. Salomon JF, Cotard JP & Viguier E, Management of urethral sphincter mechanism incompetence in a male dog with laparoscopic-guided deferentopexy. J small Anim Pract 2002; 43: 501-505.
17. Holt PE, Coe RJ & Hotston Moore A, Prostatopexy as a treatment for urethral sphincter mechanism incompetence in male dogs. J small Anim Pract 2005; 46: 567-570.