Expert Guide: How I approach Canine Urinary Incontinence

Published 26/09/2019

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Urinary incontinence is a common presentation to the small animal clinician; Rafael Nickel shares his thoughts on how to approach such cases and discusses some of the newer techniques available for treatment.

How I approach…. Canine urinary incontinence

Key Points

Successful diagnosis of urinary incontinence starts with careful questioning of the owner, followed by urinalysis and ultrasound scans of the patient.

Urethral sphincter mechanism incompetence (USMI) is the most common cause of urinary incontinence, and can usually be successfully treated with long-term medication.

Ectopic ureter, the most common cause of urinary incontinence in juvenile dogs, is often associated with USMI, which means that surgical correction alone is only successful in some cases.

Bladder malfunction and injury leading to urinary incontinence are rarely amenable to successful medical therapy but in selected cases a suprapubic permanent catheter can offer a good quality of life.

Introduction

Urinary incontinence is generally considered as a symptom, presenting as a passive, unconscious dribble of urine from the urogenital tract. There should be no discernible behavioral patterns typical of urination, and a micturition reflex is usually absent. Identification of true incontinence should narrow down the possible causes and pathophysiology, and assist in the diagnosis and assessment of potential treatments, thus allowing a standardized approach to the problem.

How do I proceed?

I tend to start with specific questions to the owner to help with classification and definition, e.g.:

Is it really a passive urine loss?
Does it occur repeatedly, only at rest or when sleeping, daily or only occasionally, or immediately after a walk? A scoring system is helpful here.
Did it first occur at a young age or only after sexual maturity?
Did it occur after neutering, deslorelin implant or similar?
Are there any issues with conscious urination?
Is there anything strange about the dog’s drinking behavior, e.g., is it polyuric/polydipsic (PU/PD)?
Is the urine light in color (especially if the dog is PU/PD), or does it have a strong smell (which can indicate urinary retention or infection)?
Are there signs of neurological deficits (e.g., locomotor disorder or weakness, impaired defecation, etc.)?

Diagnostic investigations

With the information collected, I can plan a more targeted approach and make the list of differential diagnoses more manageable. This can be rather long, as shown in (Table 1), but in order to identify the majority of possible causes quickly, easily and cheaply, in the interests of the pet and the owner, I recommend performing a minimum database, as follows:

Diagnosis	Juvenile dogs		Adult dogs		Total
	female	male	female	male
Sphincter deficiency (USMI)	64	12	235	9	320
Ectopic ureter (EU)	90	10	12	4	116
No diagnosis	6	5	12	10	33
USMI + EU	15	0	2	0	17
Prostate disease	0	0	0	12	12
USMI + detrusor instability	8	1	3	0	12
Detrusor instability (DI)**	2	0	4	5	11
Neoplasia of the bladder	0	0	5	5	10
Neurological cause	0	0	3	6	9
Cystitis	2	0	5	1	8
Pseudo-/Hermaphroditismus	5	1	1	0	7
Fistula (ureterovaginal/vesicovaginal)	0	0	4	0	4
Vaginal neoplasia	0	0	2	0	2
Pelvic abscess	0	0	1	0	1
Perineal rupture	0	0	0	1	1
Totals	192	29	289	53	563

Table 1. A survey of 563 dogs diagnosed with urinary incontinence at Bristol University *.

Urine test

A comprehensive analysis and bacteriological examination of urine from a cystocentesis sample is ideal. If the urine specific gravity (USG) is < 1.020, further tests for all causes that can lead to PU/PD should be carried out. Remember that healthy dogs will have a natural daily variation in the USG, and repeated urine samples should be taken as necessary. Although rarely the cause of incontinence, any urinary infection is significant, as it can increase the severity of the clinical signs and may adversely affect the response to treatment for the incontinence.

Ultrasound examination

Ultrasound is non-invasive, relatively cheap and commonly available. It is possible to detect structural changes to the kidneys, the course of the ureters, the size, position and contents of the bladder, and the prostate, as well as the emptying function. It is therefore useful to examine the patient with a full bladder and then again after urination. If possible, spontaneous urination should also be observed.

Ultrasound allows assessment of the amount of urine remaining in the bladder after micturition, the so-called residual urine volume. Measurement of the bladder in 3 planes (longitudinal, transversal and sagittal), multiplied by a correction factor of 0.625 and then divided by bodyweight allows for precise volume determination***. Residual amounts of urine > 4 mL/kg body weight have been shown to be associated with neurological or obstructive disease 1.

Ultrasound also allows determination of the bladder position within the abdomen. A caudally located bladder, often pear-shaped, or with an abnormal angle between the bladder neck and the proximal urethra, is a common finding in bitches with urethral sphincter mechanism incompetence (USMI). 80-87% of bitches with proven urinary dysfunction present with this condition 2. Ultrasound imaging can identify the degree of hypermobility of the bladder and urethra 3 (Figure 1).

The most common cause of incontinence in juvenile dogs is an ectopic ureter, and this can be identified sonographically in the vast majority of cases 4. Noticeable ultrasonic findings may include a ureter which follows an intramural course in the bladder wall (Figure 2), a dilated ureter and renal pelvis, and a divergent or absent “jet phenomenon”.

Figure 1. A longitudinal sonographic scan of the caudal abdomen with the hypoechogenic contents of the urinary bladder visible. The typical trough-like shape of the bladder neck cannot be identified because the pubic bone interferes with the intrapelvic image, indicating caudal positioning of the bladder or urethral hypermobility. © Rafael Nickel

Figure 2. A longitudinal sonographic scan of the caudal abdomen of a dog showing the bladder and bladder neck; the intramural course of an ectopic ureter is clearly visible within the dorsal wall of the bladder neck. © Rafael Nickel

The “jet phenomenon” describes the normal entrance of urine into the bladder from the ureters, and can often be detected on ultrasound scan. Sufficient ureteric peristalsis from concomitant urine production is necessary, and in puppies and some adult dogs it may be sufficient to offer the patient a drink before performing a scan. Alternatively, furosemide (1-2 mg/kg SC or IV) can be used to stimulate urine production. Following the injection (within a minute if given IV, or approximately 10 minutes if given SC) a longitudinal bladder scan should show a normal jet of urine in a ventrocaudal direction; in a transverse scan, the urine jet is arched, sometimes described as resembling a curved sword (Figure 3a) (Figure 3b).

Figure 3a. A sonographic scan using color Doppler mode in the area of the bladder neck. A colored jet of urine enters the bladder lumen dorsally through the uretero-vesical junction in a caudal-ventral direction, indicating normal anatomy and function. © Rafael Nickel

Figure 3b. In the transverse scan the normal jets have a “sword-like" appearance. © Rafael Nickel

Not all incontinent patients will have such findings on ultrasound examination, and other possibilities, such as uroliths, tumors, diverticula and unusual abnormalities (e.g., malformations of the urogenital tract, such as pseudohermaphroditism) may be identified.

When do I recommend further investigation?

A definitive diagnosis of urethral sphincter mechanism incompetence (USMI) cannot be confirmed by any method, including computer tomography, magnetic resonance imaging, endoscopy or with urodynamic examination techniques 2. If the history and clinical signs suggest USMI, it may therefore be appropriate to try “diagnostic therapy” as detailed below, using sympathomimetics or hormones (only in neutered dogs), as such drugs will be ineffective if the urinary incontinence is due to other causes. However, a lack of effect does not exclude USMI.

To confirm or rule out an ectopic ureter (EU), computer tomography is recommended 5 although some clinicians report cystourethroscopy is just as effective 6. Personally I only use this latter technique if ultrasound examination gives doubtful results, or if I suspect a combined EU and USMI 7, and to decide which treatment is appropriate.

If endoscopy is unavailable, I would consider retrograde contrast radiography, particularly for cases of juvenile urinary incontinence. Urethrography (in male dogs) and vaginourethrography (in female dogs) (Figure 4a) (Figure 4b) can be very helpful for detecting anatomical changes to the urethra. Urodynamic examination methods are only available in a small number of university clinics and are not a routine diagnostic option.

Figure 4a. A retrograde contrast radiograph of the lower urinary tract (urethrography) in a male dog with a urethral diverticulum. © Rafael Nickel

Figure 4b. A retrograde contrast radiograph of the vagina, urethra and bladder (vaginourethrography) in a female dog with a ureterovaginal fistula. © Rafael Nickel

Drug therapy options for USMI

In view of the high success rate and the rare side effects, sympathomimetics and estrogens are almost always my first choice for treating USMI. The drugs work by optimizing the passive resistance of the urethra during the bladder’s filling phase, and the efficacy has been assessed using urodynamic examination 8 9 10.

Phenylpropanolamine and ephedrine hydrochloride are sympathomimetics licensed for use in dogs in many European countries. Various retrospective studies have shown phenylpropanolamine to be successful in treating urinary incontinence in 75-97% of cases and ephedrine in 74-93% of cases 11 12. In a comparison with phenylpropanolamine, pseudoephredine, a diastereomer of ephedrine used in the USA and Australia, resulted in more side effects and was less effective 8. Side effects described for sympathomimetics include hypertension, restlessness, anxiety, agitation and tachycardia 8 9 10 11 12. A personal retrospective analysis of patients by Utrecht University between 1990 and 1996 showed such side effects in 24% of cases given ephedrine and in 9% of cases given phenylpropanolamine (unpublished data).

Phenylpropanolamine is dosed at 1-1.5 mg/kg q8-24h PO and ephedrine is dosed at 1-4 mg/kg q8-12h PO. One study noted that while there was no difference between a single dose slow-release formulation and repeated daily use of phenylpropanolamine 12, there was a decrease in the urethral resistance measurements after one week of treatment with the daily dosing protocol 9. A reduction in the receptor sensitivity is suspected with long-term use, but in a personal retrospective analysis, no reduction in effect was observed over a two-year period using phenylpropanolamine at 1.5 mg/kg q12h. Both drugs are less effective in male dogs than in bitches.

Estriol is authorized for the treatment of urinary incontinence in bitches in most European countries, and – in contrast to other estrogens (e.g., estradiol, diethylstilbestrol, which have a longer receptor binding time) – its use at the recommended dose has not resulted in any bone marrow depression being described to date 13. Note that estriol is only authorized for the treatment of neutered bitches, with a recommended dose of 1 mg per animal q24h PO. However, the effective dose can vary greatly between individual animals, but higher doses may result in unwanted side effects similar to a bitch in heat (i.e., attractiveness to male dogs, vulval swelling and discharge) 14. As demonstrated by urodynamic testing 10 15, the onset of efficacy is longer than that of sympathomimetics; the success rate in one clinical study was 61%, but only after some weeks of use 14.

Estrogen has an effect on the receptor binding of sympathomimetics and can therefore achieve a synergistic effect 16. Personal experience confirms the effect of combination therapy in dogs where sympathomimetics alone are no longer effective, but in one study urodynamic measurements showed that the maximal urethral occlusion pressure decreased after a week on combination therapy when compared to estriol alone 15.

In view of the high success rate and the fact that side effects are rare, sympathomimetics and estrogens are almost always my first choice for treating urethral sphincter mechanism incompetence.

Rafael Nickel

Gonadotropin Releasing Hormone (GnRH) and its analogues, such as buserelin, have been investigated for dogs with USMI 17. One study showed that 7 out of 11 bitches were continent when treated with a GnRH analogue 17. However, urodynamic examinations did not show any effect on urethral occlusion pressure and the drug was less effective than phenylpropanolamine. Interestingly, some bitches in the placebo control group also became continent. Anecdotal reports on the use of deslorelin implants (which is licensed in some countries for chemical castration of dogs) suggest it is also effective in some neutered bitches and dogs 18.

Endoscopic and surgical options for USMI

In bitches that do not respond to drug treatment, or where therapy efficacy decreases over time, or there is intolerance to medication, it may be necessary to consider mechanical methods to increase urethral resistance.

For many owners, an attractive option is endoscopic injection of bioimplants into the urethral mucosa (Figure 5a) (Figure 5b). Under general anesthesia three to four deposits of an injectable implant material (collagen or polymer) are inserted in a circular fashion, approximately 1.5 cm distal to the trigone via cystoscopy. The reported success rate is variable, although a long-term study noted 27 out of 40 bitches (68%) showed a good response over an effective period of 1-64 months (an average of 17 months). Side effects, in the form of hematuria and transient stranguria, are generally rare and moderate 19. Various bioimplants have been employed, including collagen; this is no longer available so I have used dextranomer copolymer with hyaluronic acid since 2012. A retrospective analysis of 50 bitches showed no significant difference in progression and effect between the two materials, although numerically the replacement preparation had a lower success rate at 58% 20.

Figure 5a. An endoscopic image of the mid-urethral region in a female dog with USMI which had not responded to medical management; a cystoscopic needle (5 Fr) is inserted into the urethral submucosa. © Rafael Nickel

Figure 5b. Three injections of dextranomer co-polymer and hyaluronic acid (each approximately 0.3-0.8 mL) have been placed in the submucosal layer to attain urethral “bulking”. © Rafael Nickel

Currently the most popular surgical intervention is implantation of an artificial urethral sphincter (AUS). This is a silicone collar which is inserted around the urethra to partially occlude it 21. The collar is connected to a catheter which leads to a subcutaneous port; this allows the resistance to be adjusted according to the individual needs of the patient by injection of small amounts of sterile saline solution (Figure 6). Again success rates vary, with some bitches being fully continent following the procedure, whilst others show a significant reduction in symptoms. Complications include dysuria, hematuria and urinary tract infection, and success may depend on the compliance of the owners in using the port. In one study of 27 bitches, complications led to the removal of the collar in two animals, but high owner satisfaction was reported with 22 of the animals 21. Personal experience with AUS in more than 40 female and 25 male dogs over a period of more than four years has given similar results and complications. The worst complication is if stenosis or stricture develops at the site of the collar, which requires removal. In these situations, other options such as endoscopic bioimplant injection or (less frequently) techniques such as colposuspension and/or urethropexy or vasopexy may be considered 22 23.

Figure 6. A peri-operative image during surgical placement of an artificial urethral sphincter (AUS) around the cranial urethra. The small silicone tube will be tunneled to connect to a subcutaneous port and saline can be injected via the port to allow subsequent adjustment of the pressure on the urethra. © Rafael Nickel

Detrusor instability treatment options

Urinary incontinence may sometimes result from detrusor hyperreflexia, whereby hyperactivity of the detrusor muscle during the bladder’s filling phase without an appropriate response from the urethra causes urine leakage. A definitive diagnosis requires the use of simultaneous urethrocystometry 10. In a small number of cases, dogs that do not respond to the drug therapy suggested above for USMI may respond to oxybutynin, a product indicated for use in humans suffering from detrusor instability. In dogs it is effective at a dose of 0.3 mg/kg q8h, although long-term use may cause constipation and reduced tear production.

Ectopic ureter treatment options

Evidence of an ectopic ureter in incontinent animals by imaging or endoscopy does not always mean that surgical correction will lead to continence. This is probably due to the fact that many affected bitches also have USMI 7 24. The success rate for surgical intervention can be increased significantly if the following criteria are identified 7:

The abnormal ureteral opening is situated caudal to the bladder neck or the proximal urethra.
The opening of the ureter or the associated renal pelvis is dilated.
The bladder is in a normal position.

If these criteria are not met, the likelihood of USMI is substantially higher. In such cases, phenylpropanolamine can be used on a trial basis, even in puppies. I therefore recommend drug treatment is continued until sexual maturity before further intervention. If there is an unsatisfactory outcome I will then perform endoscopic laser ablation (see below) and, if necessary, bioimplant injections into the urethral submucosa.

Endoscopic-assisted laser ablation (Figure 7) is an attractive technique for treating EU but the results are only satisfactory in male dogs 25. The technique involves transecting the medial wall of the ectopic ureter with a laser so that it opens into the bladder lumen. In bitches, where there is usually a long intramural ureter, the sphincter muscle mechanism may be compromised, which means the success rate is lower than with surgical techniques 26. Extramural ectopic ureters (which are rare) cannot be corrected using this method.

Figure 7. An endoscopic image showing ectopic ureters entering the cranial urethra. Treatment was via laser ablation. © Rafael Nickel

The classic surgical method for treating EU is ureteroneocystostomy, in which the ectopic section of the ureter is ligated or partially removed and the normal ureter portion inserted and sutured within the bladder mucosa 26. The exact implantation site is not significant, but using spatulation and special stitching techniques can largely avoid the risk of post-operative stenosis at the anastomosis site (Figure 8). An antegrade catheter inserted to ensure constant urine flow during the first 24 hours post-surgery significantly reduces the risk of complications such as dehiscence and uroabdomen. Using this method, 72% of dogs in one study became continent 26 and my own retrospective study of 20 bitches gave a success rate of 80% 27.

Figure 8. A peri-operative image during surgical correction of an ectopic ureter (ureteroneocystostomy). The abnormal section of the ureter has been ligated and dissected, and the remainder of the ureter is pulled through a stab incision in the bladder wall and anchored to the mucosa with simple interrupted sutures using 4-0 or 6-0 USP monofilament resorbable material. © Rafael Nickel

Bladder dysfunction treatment options

Inadequate emptying of the bladder often leads to urinary incontinence, with the classic form known as overflow incontinence. However, sometimes a dog can appear able to urinate, with partial emptying of the bladder, due to increased intra-abdominal pressure. Some of the underlying causes, such as intervertebral disc disease and spinal cord trauma, are reversible, but prolonged overstretching of the bladder, which can occur with both functional and mechanical obstruction, can result in irreversible damage to the detrusor muscle. Idiopathic paralysis of the bladder is also a possibility.

Regardless of the cause and the prognosis, management of these cases requires the bladder to be emptied at least once a day. In contrast to cats, physical expression is unsuccessful in the majority of dogs, and it is necessary to use either intermittent catheterization or implant a permanent indwelling catheter. Intermittent catheterization can present technical and logistical problems; it may be possible for a pet owner to catheterize a male dog, but it can be much more difficult in small bitches. In addition, long-term intermittent catheters can cause many animals to develop infections which can lead to death or euthanasia 28.

A suprapubic catheter technique has proven to be a relatively uncomplicated method to treat this condition and is generally well accepted by owners. Surgery involves making a very small incision to place a Foley catheter within the bladder, exteriorizing the catheter via a subcutaneous tunnel. Typically I use a catheter 30 cm in length, with about 20 cm retained within the patient. Regardless of the size of the animal, I prefer to site the catheter exit cranial to the umbilicus wherever possible (Figure 9). The long subcutaneous route acts as a barrier to ascending infection and allows a better passive closure. The connective tissue canal formed around the catheter becomes fibrous over time, which assists with the subsequent replacement of the catheter. I routinely recommend this is done after 3 months for aseptic and technical reasons, and if a large diameter catheter (e.g., > 12 Charr./Fr.) is used this makes removal or replacement easier. The balloon at the catheter tip holds the catheter in position within the bladder and is inflated using isotonic saline, usually between 3-15 mL. Management requires careful handling of the tube and drainage of the bladder several times a day. Complications include accidental catheter removal or damage (in ~15% of cases) and infection (in ~20% of patients) 29. Over a 5-year period I have successfully performed 35 such operations, 14 of them for neurological causes and 21 with obstructive neoplasia of the urethra.

Figure 9. Surgical placement of a Foley catheter in the bladder with a subcutaneous tunnel to the exterior for long-term management of bladder paralysis in a male dog. © Rafael Nickel

* Holt PE. Urinary incontinence in dogs and cats. Vet Rec 1990;127:347-350.
** Suspected diagnosis or as a result of cystometry investigations.
*** Lisciandro GR, Fosgate GT. Use of AFAST Cysto-Colic View urinary bladder measurements to estimate urinary bladder volume in dogs and cats. J Vet Emerg Crit Care 2017;27(6):713-717.

Canine urinary incontinence is a significant problem which affects the quality of life for both the animal and the owner. It can lead to serious health problems and it is not uncommon for affected dogs to be rehomed or euthanized. Initial ultrasound examination allows many causes to be recognized and treated in a targeted manner, and for the commonest causes of incontinence there are a multitude of treatment options with acceptable success rates and few serious complications.

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Rafael Nickel

Professor Nickel qualified from Hannover Veterinary School in 1983 and his career has spanned research, small animal practice and academia. Read more