Introduction
Urinary incontinence can be a significant problem in many dogs, particularly in the spayed female. Urinary incontinence has been reported to develop in more than 20% of all spayed female dogs and 30% of spayed females in dogs weighing more than 20 kg. The incidence of incontinence also increases with age.
Urinary incontinence can lead to a severe disruption to normal lifestyle, especially if the dog normally lives within the household. Even small amounts of urine leakage onto bedding, carpets or other household items can be distressing and intolerable for the owner.
Interpretation and misconceptions
Successful management of the incontinent dog requires a clear understanding of the problem. Very often the term ‘incontinence’ is used to describe any change in urinary pattern or when urine spots are noted around the house or in the dogs bedding. In reality, ‘incontinence’ can have many different clinical presentations and are caused by a variety of aetiologies. Sphincteric weakness in the female dog is perhaps the most common cause of urinary incontinence in the older dog, but the role of exacerbating factors (e.g. polyuria/polydipsia, obesity, urinary tract infection) must not be ignored. Other dogs are incontinent because of bladder “over-flow” caused by either neurological deficits or as a consequence of outflow obstruction. Prostatic disease (in any of its various forms) can disrupt normal urinary control. Ectopic ureters are a most common congenital cause of incontinence, but other anatomical and functional defects can exist to cause incontinence in the puppy. Finally, urinary tract infection can create an irritable bladder, which can induce an urge incontinence.
Appropriate treatment requires proper diagnosis of the type and cause of incontinence. In almost all cases, careful history taking allows precise elucidation of the nature of the apparent ‘incontinence’. The following terminology is useful to allow clear communication of disorders to micturition.
| Haematuria | presence of blood or red blood cells in the urine |
| Dysuria | difficulty in passing urine, often associated with pain |
| Pollakiuria | abnormally frequent passage of urine |
| Stranguria | excessive straining or unproductive attempts to pass urine |
| Polyuria | increased volumes of urine. Usually associated with a primary or obligatory polydipsia |
| Urge incontinence | Inappropriate urination associated with irritation/reduced storage capacity of the bladder |
| Stress incontinence | Inappropriate urination associated with periods of increased abdominal pressure |
Diagnostic procedures must evaluate both structure and function of the urinary system in a diagnostic approach based upon the clinical signs.
Types of conditions
1. Anatomic causes
Failure of normal ureteric implantation into the bladder represents one of the more common anatomical causes of incontinence in the dog. Ectopic ureters may be unilateral or bilateral, and either intramural or extramural. Extramural ectopic ureters bypass the trigone and directly enter the lower urinary tract distally. Intramural ectopic ureters enter the serosa of the bladder at the normal trigone location and then travel within the wall of the trigone and urethra until it enters the urethral lumen distal to the bladder neck. Various other malformations of the ureteric stoma may be seen occasionally (e.g. ectopic ureteral trough, ureterocoele). Failure of the urachus to close following birth can lead to various sized defects in the mucosal lining about the bladder apex. Disruption to normal micturition may be seen if the urachal remnant remains patent with the lumen of the bladder. Other abnormalities include vestibulovaginal anomalies.
2. Sphincteric incontinence
The ‘classical’ stress incontinence occurs due to failure of the urethral sphincter to oppose increases in bladder pressure. Urine floods passively from the urethra whenever pressure in the bladder exceeds effective closure pressures of the urethra. Nearly all dogs affected with this condition will be described as dribbling during sleep or when recumbent. Because up to 75% of incontinent dogs developed their condition within 3 years of ovariohysterectomy, the surgery itself is often blamed directly for the condition. Incontinence is associated with incompetence of the urethral sphincter, but the clinical manifestation of the condition is almost certainly multi-factorial in nature. Some anatomical predispositions have been recognised in the dog. (e.g. the presence of the bladder neck within the pelvic cavity and shorter urethral lengths).
3. Urinary bladder storage dysfunctions
Disruption to detrusor function can manifest clinically as either an inability to fully contract the bladder (i.e. high residual bladder volume after attempts to urinate, a so-called Full Bladder Incontinence, or overflow incontinence) or as increased bladder irritability (so called empty bladder incontinence). In this latter instance, the apparent incontinence should be more accurately interpreted as pollakiuria (conscious frequent effort to pass small amounts of urine).
Full-bladder incontinence is perhaps more commonly associated with spinal cord disease. Dogs with upper motor neuron deficits often have an inability to detect, coordinate, and initiate bladder contraction. Urethral tone is probably high, increasing the challenge of bladder contraction to produce a high enough pressure to overcome urethral resistance. Animals with lower motor neuron deficits can have a flaccid, over-distended bladder with weak urethral resistance. Both types of neurological dysfunction produces full bladders and over-flow incontinence. Usually, significant other neurological deficits to the hind limbs accompany the urinary signs.
‘Full bladder incontinence’ can also develop without the presence of obvious neurological deficits in other body systems. This may develop as a result of increased outflow resistance (e.g. transitional cell carcinoma, prostatic disease) which leads to a chronically distended bladder that fails to contract normally even after relief of the outflow obstruction. A few dogs are thought to have an idiopathic detrusor failure. Some of these are assumed to be the result of an undiagnosed neurological problem (perhaps a focal neuropathy), or as a consequence of a transient over-distention of the bladder which causes disruption to normal tight junctions within the detrusor muscle.
Empty-bladder incontinence (or urge incontinence) typically occurs with inflammatory disease affecting the bladder or urethra. Pain, discomfort, or reduced elasticity of the bladder limits its role as a storage organ. The animal is therefore observed to pass small volumes of urine (or strain unproductively) on a regular basis. On physical examination, the bladder is not palpable.
Diagnosis of incontinence
History & clinical examination
Thorough history taking and physical examination are essential to develop the initial diagnostic plan. In almost all cases, an understanding of the nature of the incontinence can be elucidated from the history and description of the apparent incontinent episodes.
Historical questions should include the age and time of onset, the progression of signs, related health changes, time of incontinence (at rest, continually, when stressed, prior to urination, following urination), whether the animal consciously attempts to void, adequacy of faecal control, history of urinary tract infections, reproductive status, history of medication, and diet (especially any recent changes in formulation (e.g. moist to dry). Specific questions regarding water intake (amount, recent changes etc) are also very important. These questions provide significant clues to whether the problem is likely to be a functional or structural in nature, and whether there could be any systemic factors which may be exacerbating the condition. Ideally, micturition should be directly observed by the clinician.
A full physical examination should be performed, prior to performing a specific examination of all elements of the urogenital tract. An important aspect of the physical examination is an evaluation of bladder size, especially after the animal has attempted to void. Digital pressure should also be applied to the bladder to determine the capacity for the urethra to resist increases in detrusor pressure. Documentation of residual volume by catheterisation or by imaging techniques should be performed, especially if overflow incontinence is suspected from the history. Consistently empty bladders are more typical of a low urethral sphincter tone, ectopic ureters, or an unstable bladder due to cystitis. Rectal examination should always be performed to allow digital evaluation of the urethra, prostate and vagina. If possible, digital and visual inspection of the vulva and vagina should also be performed.
Laboratory testing
A urinalysis must be performed as standard in the investigation of all incontinent dogs. Estimation of urine specific gravity will provide clues to the possibility of underlying systemic disease (e.g. endocrine polyuria). A sediment examination will permit detection of inflammatory disease, crystalluria and possible renal involvement. Ideally, urine culture and sensitivity should be done even in those dogs without a diagnosis of urinary tract inflammation based on sediment examination. The preferred method for urine collection is cystocentesis, but this should be performed with care in animals with overdistended bladders as persistent leakage can occur. A routine blood screen (biochemistry and haematology) should also be performed, especially if abnormalities are detected on urinalysis, if physical examination reveals the possibility of systemic disease or in all dogs over 8 years of age presenting with a recent onset of incontinence.
Imaging studies
In almost all cases of incontinence, radiographic evaluation of urinary tract anatomy forms an essential component of case management. Considerations of the type of radiographic evaluation, and when it should be performed in the sequence of diagnostic investigations will vary depending on the individual case and client circumstances. Radiographic evaluation should certainly be considered if symptomatic medical management of the incontinence is ineffective.
A variety of structural and functional defects can cause incontinence, and the presenting signs for many of them may be very similar. It is therefore essential that, once a decision has been made to perform a radiographic investigation, the clinician perform a complete radiographic evaluation of the affected region. Contrast studies are essential, as plain radiographs alone are usually insufficient to provide an adequate explanation for the animal’s complaint. For example, radiographic evaluation of bladder masses is improved when either positive or negative contrast is added. Double contrast may be required to outline soft tissue lesions. Urethral lesions are best evaluated by positive contrast studies of urethrogram in the male and a retrograde vaginourethrogram in the female. Excretory urograms and retrograde vaginourethrograms are useful for ectopic ureter diagnosis.
Ultrasonography
Ultrasonography is a very useful imaging technique for detecting abnormalities in the structure of the kidneys, bladder, prostate, and urethra. Although it can be very effective at detecting obvious structural defects (renal morphology, ectopic ureter, calculi, neoplastic lesions, prostatic diseases, etc) it should be considered as complementary (rather than superscedant) to the radiographic evaluations already described. The accuracy of ultrasound investigation is very operator dependant, and false-negative (and false-positive) diagnosis can be obtained by inexperienced operators. Ultrasonography can be used to help increase the diagnostic accuracy of fine-needle aspiration and biopsy by aiding in the localisation of specific lesions.
Urodynamic studies
Urodynamic studies that have been investigated in the dog include urethral pressure profilometry (resting and stressed), cystometry, and electromyography. Cystometry has been used in small animal medicine for 30 years and urethral pressure profilometry for over 20 years. The cystometrogram aids in determining if the bladder responds with a micturition reflex. Dogs with an irritable bladder may have multiple, brief contractions that frequently fail to produce voiding. Such patients frequently present with either urge incontinence or pollakiuria. Urethral pressure profile (UPP) is most useful to evaluate urethral sphincter tone in the dog. When performed in dogs with prostatic disease in male dogs, or in female dogs with ectopic ureter a low maximal urethral pressure on the UPP can predict postoperative incontinence.
Urodymanic studies improve our understanding of functional causes of urinary incontinence, and can be used to demonstrate the site of abnormal function of the lower urinary tract and (in theory) should enable more precise diagnosis of the (functional) cause of incontinence. However, because the testing is associated with a variety of variations and artefacts, many experienced operators consider urodynamic studies to be of academic interest only. It is generally considered that the results of a urodynamic study are unlikely to change selected clinical treatments that have been decided from the results methods of patient evaluation described above.
Endoscopy
Urethrocystoscopy can be used to visualize, and to biopsy, lesions of the urethra and bladder, to identify ectopic ureters, and to catheterize the ureters for individual collection of urine samples. The usefulness of this procedure, however, is somewhat limited because specialised equipment is necessary. However, it is possibly the ‘gold standard’ in terms of diagnosis of ectopic ureters and can assist greatly with the diagnosis of a variety of other disorders that other modalities are unable to resolve.