Update on urinary incontinence and alternative therapies (Proceedings)

Urinary incontinence is a common problem affecting up to 20% of spayed female dogs and 30% of those > 20 kg. In most of these patients it occurs within 3 years of spaying, although in many it may not become a major problem until later in life when it can be complicated by diseases that increase water intake and urine production. The few studies that have evaluated age of neutering and risk of incontinence indicate that dogs neutered after the first estrus may be at greater risk of developing urinary incontinence than those neutered before the first estrus. Among the most common breeds affected are the Old English sheepdog, Doberman pinscher, Boxer, German Shepherd Dog, and Weimeraner. There are several reasons for urinary incontinence, including ureteral ectopia and detrusor hyperreflexia (over-active bladder), but the most common in the dog is urethral sphincter mechanism incompetence (USMI).

History

A careful history must be taken when discussing incontinence with pet owners. It must be distinguished from behavioral problems, polyuria, or pollakiuria (small frequent urinations which are usually indicative of inflammation/infection in the lower urinary tract), and it is important to establish that the animal is unconscious of the passage of urine. Patients whose incontinence has developed along with an increase in water intake should be further evaluated for disorders causing polyuria and polydipsia.

Clinical Examination

Most dogs with USMI (both male and female) have no difficulty urinating and appear otherwise healthy. It may be of benefit to observe the patient urinating and to palpate the bladder after voiding to determine if it has been completely emptied. If it is still full, it is worth passing a urinary catheter to measure residual urine volume (normal is < 0.4 ml/kg). This may indicate a neurologic or obstructive problem and overflow incontinence. Careful neurologic evaluation of the perineal region and rectal examination and palpation of the urethra are also important in ruling out problems such as sacral spinal cord lesions, neoplasia, and proliferative urethritis.

Diagnosis

All patients with urinary incontinence should receive a urinalysis with sediment examination and a urine culture. While the leakage of urine may be exacerbated by a urinary tract infection, the incontinence itself may predispose the patient to a UTI. Bloodwork is indicated if the patient has decreased urine concentration, particularly in the face of dehydration. Imaging should be considered to determine if the dog has a "pelvic bladder" which is shifted caudally, preventing normal abdominal pressures from reaching the proximal urethra. Imaging or urethrocystoscopy is also of value to rule out ectopic ureters as the cause for incontinence.

Treatment Plan

Medical Therapy

In the majority of urinary incontinence cases, otherwise healthy patients are treated initially with either alpha-agonist medications such as phenylpropanolamine (PPA) or estrogen compounds like DES or Premarin. Alpha-agonists increase the stimulation of the adrenergic receptors on the internal urethral sphincter while estrogens may up-regulate the expression of such receptors. There is some evidence that the two drugs in combination may be synergistic and benefit patients who do not respond to either drug alone. We strongly recommend performing a baseline systolic blood pressure before starting PPA and do not use it in patients with hypertension, renal disease, or cardiac disease. Hypertension is a potential side effect of alpha agonist therapy. Other adverse effects include restlessness, aggression, decreased appetite, and insomnia. Side effects of estrogen therapy primarily are related to bone marrow suppression. Patients receiving either of these medications should be closely monitored for these side effects.

There are several new medical therapies that have the potential to benefit dogs with USMI. These include selective serotonin reuptake inhibitors (duloxetine) and gonadotropin-releasing hormone analogues. Further evaluation of these is ongoing and may increase the therapeutic options for these patients.

Male dogs with urinary incontinence pose a more difficult challenge. Less than 50% of male dogs respond to medical therapy, and the most successful treatment is PPA. Testosterone cypionate has had some anecdotal use and may provide some improvement.

Dogs who are not responding to appropriate medical therapy should be evaluated for other lower urinary tract disease via imaging including abdominal ultrasound and/or contrast radiography. We routinely perform cystoscopy in patients with urinary incontinence to rule out anatomic abnormalities which may be contributing to clinical signs. Urodynamic evaluation can be performed to rule out over-active bladder and confirm the diagnosis of USMI.

Non-medical/Surgical Intervention

Patients who cannot tolerate or do not respond to medical therapy may be candidates for urethral collagen injections. This cystoscopic procedure involves placing small blebs of collagen under the urothelium, effectively narrowing the urethral diameter. Previous retrospective evaluation of the procedure has shown it to be effective for improving incontinence in 55 – 75% of female dogs for an average of 15 months. It has also been used with success in male dogs and in patients who are incontinent after ectopic ureter correction. Urethral collagen injections may be performed in males antegrade through a cystotomy incision, however, there has not been formal evaluation of this procedure and its overall success rate is unknown. In the next year, bovine cross-linked collagen is expected to be phased out and replaced with one of several other injectable agents currently on the human urology market. There is little data on these agents in veterinary clinical cases now, however several studies are in process and we expect to see published results soon.

Surgical therapy of urinary incontinence has previously focused on increasing the transmission of intraabdominal pressure to the proximal urethra and improving the stability and pressure within the urethra. Colposuspension, which attaches the uterine remnant to the pelvic ligament and thus draws the bladder neck and proximal urethra further into the abdomen, has been found to have variable success (~50%) and has a high failure rate due to breakdown of the attachment to the pelvic ligament.

Recently, the development of a new surgical technique which uses an adjustable vascular occluder has given us another option for both male dogs (who respond poorly to medical therapy overall) and females who fail medical therapy. One study showed improvement in 11/11 dogs treated with this device and complete continence in 7/11 (67%). The long term outcome and durability of this procedure has yet to be determined, but it is promising and is becoming more widely available.

On the horizon are potentials for adapting one of the most commonly used surgical techniques in women to the female dog to correct urethral incompetence. In human urology, there are several variations on the transobturator vaginal tape (TVT) procedure which is designed to pull the vagina anteriorly to the pelvis, increasing the pressure in the urethra which sits between the two. Last year the results of 7 dogs treated with the TVT procedure were published with promising results. It is hoped that this procedure may also provide another option for patients which fail medical therapy.

Urinary Incontinence Algorithm

References

Adin CA, Farese JP, Cross AR et al. Urodynamic effects of a percutaneously controlled static hydraulic urethral sphincter in canine cadavers. American Journal of Veterinary Research. (2004) 65:283-288.

Berent A, Weisse C, Adan C, Todd K. The use of a percutaneously controlled hydraulic occlude for the treatment of urethral sphincter mechanism incompetence in 11 dogs and 1 cat. Abstract. Proceedings of the ACVIM Forum. Montreal, Canada (2009) page 686.

Claeys S, de Leval J, Hamaide A. Transobturator vaginal tape inside out for treatment of urethral sphincter mechanism incompetence: preliminary results in 7 female dogs. Veterinary Surgery. (2010) 39:969-979.