Urinary incontinence is a common problem, occurring with an incidence of 10-20% of female dogs after ovariohysterectomy.
Complete diagnostic evaluation of urinary incontinence involves imaging studies to rule out anatomic abnormalities and functional studies to rule out sphincter mechanism incompetence.
Medical therapy with alpha adrenergic agonists is successful in approximately 70% of dogs with urinary incontinence. Current methods for surgical therapy are highly successful in the short term, but longterm success has been unsatisfactory.
Urinary incontinence occurs with alarming frequency in dogs, particularly in spayed females. Retrospective studies have reported that the incidence of urinary incontinence in dogs following ovariohysterectomy ranges from 13.6% to 20.1%. The significance of urinary incontinence in an indoor pet cannot be underestimated, as the problem can often lead to euthanasia due to repeated house soiling. Thus, urinary incontinence is a common problem with serious consequences; it is the responsibility of veterinarians to be familiar with its diagnosis and treatment.
It is also important to differentiate the loss of voluntary control from behavioural changes or recent onset of polyuria and polydipsia. Previous response to (or lack of response to) antibiotics or anti-inflammatory drugs may suggest the nature of an underlying condition. It is helpful for diagnostic direction and assessment to characterize the animal’s ability to initiate a urine stream, the diameter of the stream, any interruptions of the stream, and any apparent pain.
Causes for urinary incontinence
The causes of urinary incontinence may be divided into two categories: anatomical abnormalities and functional abnormalities. The anatomical abnormality that is most often associated with urinary incontinence is ureteral ectopia. Suspicion of the ectopic ureter is highly dependent upon history and physical examination of the animal, as this problem occurs almost exclusively in female dogs and is characterised by constant dribbling of urine since birth.
An early none-intrusive test can be conducted with this piece of kit.
Functional abnormalities causing urinary incontinence may be congenital or acquired, but most commonly involve urethral sphincter mechanism incompetence (USMI), otherwise known as “hormone responsive incontinence”. In contrast to ureteral ectopia, USMI typically occurs in middle-aged spayed female dogs and is characterised by intermittent incontinence during recumbency and sleep. Other factors such as polyuria/polydipsia, urinary tract infections and vaginal strictures can exacerbate pre-existing incontinence but are rarely primary causes.
One purportedly simple method of diagnosing USMI is by the response to treatment (typically with phenylpropanolamine). This method is not as simple as it seems, because a lack of response to treatment does not rule out USMI- up to 30% of dogs do not respond to pharmacologic therapy. In addition, many dogs require dosage adjustments and up to 4 weeks of drug therapy before a response is noted.
Diagnostic evaluation of urinary incontinence is focused primarily on identifying these anatomical or functional anomalies. Anatomic abnormalities may be identified through a number of imaging techniques. Initial screening examination is typically performed by use of survey radiography or abdominal ultrasonography.
Abdominal ultrasound findings consistent with ureteral ectopia include hydronephrosis or hydroureter on the affected side. In chronic cases, parenchymal and renal pelvic changes may be suggestive of pyelonephritis. Intravenous contrast urography is the classic method for identification of ectopic ureters. However, the technique is time-consuming and can be difficult to interpret.
Many vets have switched to the use of computerised tomography (CT) after intravenous contrast administration. This technique is less labour intensive than performing staged radiographs, does not require removal of faeces from the colon and allows specific localisation of the entry point of ectopic ureters. Disadvantages of CT excretory urography are that it has limited availability, adds to client expense and requires general anaesthesia.
A final method for definitive identification of ectopic ureters is direct visualisation via cystoscopic evaluation. This technique is considered the “gold standard” and has high sensitivity and specificity, but requires expensive equipment and a high skill level to obtain a complete examination of the urinary tract.