Urinary Incontinence in Dogs

Normal urination (micturition) depends on the coordinated action between the sympathetic, parasympathetic and somatic nervous systems and central control centers. Urinary incontinence is the involuntary action that results in urine leakage. Causes of urinary in continence includes lower urinary tract infections, kidney disease (congenital or acquired), neurologic disease, and anatomic disease congenital or acquired.

Small Bladder Incontinence

The anatomic causes of urinary incontinence are more common and result in small bladders.

Ectopic ureters (EUs) are the most common cause of urinary incontinence in young dogs. An ectopic ureter is defined as a ureteral opening in any area other than the normal position in the trigone of the bladder. Urinary incontinence is the most common clinical sign in dogs with EUs and is usually diagnosed in dogs prior to one year of age; however, EUs should be considered in any dog with urinary incontinence, particularly when the history is unknown.

A diagnosis of ectopic ureters can be made by abdominal ultrasound, cystoscopy, helical computed tomography (CT) or a combination of these diagnostic procedures. The latter two appear to be the diagnostics of choice based on two recent studies. Cystoscopy is a minimally invasive tool that allows easy access to the lower urinary tract and visualization of the abnormality. If necessary, contrast can be injected through the scope to provide further imaging studies. Urine cultures should always be performed in dogs with suspected ectopic ureters because urinary tract infections appear to be quite common with this disorder. The treatment for ectopic ureters is laser ablation.

Urinary Tract Infection: The inflammation associated with a urinary tract infection can cause a sensory hyperreflexia in the bladder, leading to involuntary hypercontractility. Other signs of urinary tract infection, including pollakiuria and stranguria are usually present.

Infiltrative Bladder Disease: Lesions that affect and irritate the bladder wall, like chronic cystitis, neoplasia, urolithiasis, can cause urinary incontinence. As with a UTI, others signs of lower urinary tract disease like pollakiuria, hematuria, stranguria, and dysuria are usually present.

Prostatic Disease: Because the internal urethral sphincter is located within the prostate, any sort of prostatic disease can lead to incontinence.

Large Bladder Incontinence

Lower Motor Neuron Disease: A lesion of the sacral spinal cord, sacral nerve roots, or pudendal nerve can affect the parasympathetic innervation of the bladder, impairing detrusor muscle contraction. Internal sphincter tone can remain intact since the hypogastric nerve originates from the lumbar segments. As the bladder distends, the intravesicular pressure becomes great enough to overcome the sphincter pressure, and overflow incontinence results. Because the sensory component of the urethral innvervation is disrupted by sacral lesions, the internal sphincter does not respond to increased bladder pressure. The bladder tends to be distended and flaccid but easily expressed. Other signs of sacral lesions (i.e., paraparesis or paralysis, decreased anal tone and perineal reflexes, fecal incontinence, and loss of tail tone) are usually present.

Upper Motor Neuron Disease: Lesions of the thoracolumbar region or higher can result in urinary dysfunction characterized by a distended, firm bladder that is difficult to express. Loss of inhibition of pudendal nerve activity causes a urethral sphincter hyperreflexivity. Bladder function is lost. If the pelvic and pudendal nerves are intact, reflex detrusor contraction occurs but may not be coordinated with sphincter relaxation, resulting in interrupted, incomplete urination and urine retention. Other signs of thoracolumbar disease (proprioceptive deficits, paraparesis or tetraparesis, ataxia, and hyperreflexia) may be present.

Brain Stem Lesions: Brain stem lesions cause bladder signs similar to an upper motor neuron disorder. Other signs of brain stem disease, like change in mental status, gait, posture, and cranial nerve deficits may be present. Lesions higher than the pons affect voluntary urination. Unconscious urination, nocturia, and urination in inappropriate places are common signs.

Detrusor Atony: A distended flaccid bladder that is easily expressed is the characteristic of detrusor atony. Dogs may posture to urinate and apply abdominal press yet fail to produce an adequate urine stream. As the bladder becomes distended, overflow incontinence results. Causes of detrusor atony include neurologic disease or obstruction. With neurologic disease, there is a failure to initiate contraction. With obstruction, which can be acute or chronic, and complete or partial, the overdistension of the bladder stretches the detrusor muscle, damaging the tight junctions, rendering it incapable of contraction. This condition may also be seen with dysautonomia, a very rare condition that affect the autonomic nervous system.

Diagnostic Tests

A thorough history and description of the pattern of urination helps select appropriate differential diagnoses for a micturition disorder. This frequently involves careful questioning of the owner or caretaker. Bladder size on physical examination helps divide cases of incontinence into large bladder or small bladder. Other information to gather by physical examination includes neurologic function, particularly evaluating for proprioception, anal tone, perineal reflex, and tail tone. A wet perineum, perineal staining, or urine scalding is evidence of incontinence. Rectal palpation detects prostatic disorders and urethral thickening that may suggest neoplastic or granulomatous infiltration. A digital vaginal exam may reveal strictures or mass-like lesions.

For patients with a large bladder on presentation, manual expression of the bladder gives an indication of urethral resistance. Measurement of residual urine volume after voluntary voiding helps localize the lesion. Easy of urinary catheterization can sometimes localize a lesion or establish that the lesion is functional, not structural.

Urinalysis provides indications of urinary tract infection or inflammation. A urine culture will reveal urinary tract infections that may be causing the incontinence or may be a result of the incontinence. A serum chemistry panel will help evaluate for renal damage from urinary obstruction.

Unless radioopaque calculi are present, survey abdominal radiographs are unlikely to reveal the cause of the incontinence. However, because uroliths are a common disorder, radiographs are a prudent screening tool. It is important to include the entire urethra in the view to avoid overlooking a lesion. Ultrasonography is a non-invasive method of structural evaluation the lower urinary tract that can visualize bladder neoplasia, bladder wall thickness, and intraluminal structures such as calculi. It cannot evaluate the urethra. Cystoscopy can be a valuable tool in evaluating incontinent dogs and possibly cats.

Treatment

Correction of any structural disorders identified with the diagnostic work-up will likely be necessary to cure the incontinence (e.g., cystotomy for cystic or urethral calculi). In many cases, however, correction is not possible (e.g., extensive infiltrative urethral neoplasia) or does not result in complete resolution of the incontinence (e.g., sphincter damage secondary to ectopic ureter despite reimplantation into the bladder). Incontinence caused by inflammation secondary to urinary tract infection should resolve as the UTI is controlled. With many neurologic disorders, supportive care is paramount to managing the bladder and avoiding complications. Chronic urine retention leads to detrusor atony, which can be a permanent disorder that persists even after improvement of the primary neurologic lesion. Chronic urine retention also leads to recurrent infection, which can become resistant if inappropriate or inadequate antimicrobial therapy is used. Many patients with chronic urine retention develop resistant infections despite appropriate therapy.

Medical management can be used for certain functional disorders, as an adjunct to supportive care or surgical correction, or for palliation for cases where there is no effective therapy for the underlying cause.

Conclusion

Canine incontinence can be extremely frustrating and urine-stained carpets, sofas, and bedding can quickly lead to aggravation with both the pet and veterinarian. The most common causes of incon­tinence can be easily diagnosed and, in most cases, adequately treated with medication, although some cases may be difficult to discern.