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Diagnosing Canine Urinary Incontinence (First of 2 Parts)

Stefano Romagnoli, DVM, MS, PhD, Diplomate ECAR, University of Padova, Italy

Urology & Nephrology

|November 2007|Peer Reviewed

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First of 2 Parts

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Definition
Urinary incontinence (UI) is the involuntary loss of urine during the filling phase of the bladder during recumbency and/or standing.

Signalment
• Dogs of any age or sex may present with UI but it is more prevalent in spayed females (accounting for about 80% of adult cases), female dogs spayed prior to 3 months of age, and tail-docked bitches.
• UI became more common in Europe and the United States during the second half of the last century as gonadectomy was more frequently used to control canine overpopulation.
• UI is sometimes observed in prepubertal dogs due to congenital conditions.

Causes
Adult Dogs
• Urethral sphincter mechanism incompetence (USMI)-a reduced urethral closure that commonly develops after spaying
• Bladder neoplasia
• Vaginal neoplasia
• Prostatic surgery
• Ureterovaginal fistula
• Acquired neurologic condition
• Chronic urine retention
• Detrusor instability

Prepubertal dogs
• Ureteral ectopia
• Congenital USMI
• Bladder hypoplasia
• Intersex condition
• Pervious urachus
• Congenital neurologic condition

Risk Factors
Previously continent animals
• Gonadectomy
• Prepubertal gonadectomy in females, especially if performed prior to 3 months of age
• Surgery to uterus, prostate, bladder, or urethra
• Tail docking in females

Pathophysiology
• Gonadectomy in female dogs causes a steady increase in pituitary secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH), as well as a progressive lowering of serum estrogen concentrations. The role of increased LH and FSH in UI is still not clear; however, decreased estrogen secretion can cause:
- Weakening of the canine external urethral sphincter (musculus urethralis), which lowers urethral pressure and the bladder-emptying pressure threshold
- Atrophy of the urethral mucosa
- Reduced blood flow to the urogenital system
- Reduced response of sympathetic α-1 adrenergic receptors (which are estrogen-sensitive) that mediate contraction of the canine external urethral sphincter.
• The action of the bladder center in S1 - S3 may be decreased by lower abdominal/pelvic trauma or surgery that can alter nerve supply to the urethra and also to the pelvic diaphragm, which provides periurethral support.
• Prostatic surgery is commonly associated with development of UI following prostatectomy (incidence of 95% to 100%) and less drastic procedures, such as placement of a penrose catether (incidence of 10% to 20%).
• In ovariohysterectomized (not ovariectomized) bitches, UI that develops shortly after surgery may be the result of an iatrogenic ureterovaginal fistula.
• In prepubertal animals, one or both ureters terminating at the apex of the bladder neck, the level of the urethra, or the cranial vagina can cause continuous dribbling of urine.
• Pathologic development of the urogenital system in intersex conditions can cause UI.

Signs
• History
- Loss of urine during sleep, while recumbent, and/or standing
- Presence of wet perineum, staining of perineal hair, urine scalding, urine odor
- Intermittent or constant dribbling after urination
• Physical examination
- Abdominal palpation to check for bladder neoplasia and to assess thickness, tone, and fullness of the bladder. Low urethral resistance to manual expression of urine during transabdominal palpation indicates a urine storage disorder.
- Rectal and vaginal palpation to assess thickness/tone of the urethral wall and rule out nonneurogenic causes of UI (eg, vulvovaginal strictures)
- Residual urine volume (RUV) calculation after voiding (normal is 0.2 to 0.4 ml/kg) using a urethral cathether or ultrasound
- Neurologic examination to check anal tone, perineal reflex, and bulbocavernosus reflex (all dependent on an intact sacral reflex arc and intact pudendal nerve)
- Radiographic assessment to determine whether the bladder is within the pelvis or in the abdominal cavity is not considered relevant to diagnosis or to choice of treatment.

Pain Index
• Pain is not generally associated with UI. However, a well trained dog may perceive that it is behaving abnormally and causing its owner disappointment, which may be stressful for the animal.
• Chronic UI can cause urogenital discomfort or pain due to urinary tract infection.
• Bladder/vaginal neoplasia can cause pain, although this is often difficult to assess.

Diagnosis

Definitive Diagnosis
• In adult spayed bitches, loss of urine-most commonly during sleep or while recumbent-is highly suggestive of USMI.
• The objective test to confirm USMI is a urethral pressure profile (UPP), which requires general anesthesia to introduce a bladder catheter equipped with a pressure sensor that is drawn out the urethra at a constant speed while recording pressure exerted by the urethral wall. Because UPP requires specialized equipment, commonly accepted methods to diagnose USMI include ruling out other causes of UI and treating for USMI and determining whether the patient responds.

Differential Diagnosis
• Assess behavior at micturition (see Table)
• Contrast radiographic studies of the urogenital tract are important to characterize the type of UI and are mandatory if surgery is considered as a treatment. Also, an excretory urography should be considered for:
- Young dogs (ureteral ectopia accounts for almost 50% of prepubertal cases)
- Adult male dogs, as ectopic ureters in males may go unnoticed for months or years before causing UI.
• Retrograde vaginography or urethral endoscopy may be helpful in bitches refractory to treatment to investigate possible anatomic modifications (eg, vaginal strictures), vaginal leiomyomas or leiomyosarcomas, or transitional carcinomas of the urethra (all reported as causes of canine UI).
• In cases where USMI is first in the list of differentials (such as a neutered adult bitch with a recent onset of UI only while recumbent), a treatment course with estriol or α-adrenergic drugs can be started prior to performing elaborate radiographic studies.

Gonadotropin-Releasing Hormone Agonist Stimulation Test
Collect a blood sample, then inject 50 µg of GnRH IV and collect a second sample 1 hour later; assay serum testosterone on both samples. Normal values for males are
0 ng/ml to 4 ng/ml in basal samples and 1 ng/ml to 4 ng/ml in the post-GnRH sample, while in bitches testosterone is generally very low (< 1ng/ml), especially on the
post-GnRH sample.

Laboratory Diagnosis
• Urinalysis is important because both cystitis (bacteria or inflammatory cells in the sediment) or polyuria (low urine specific weight), may cause or be a complicating factor for UI.
• Urine culture and antibiotic sensitivity tests can rule out a bacterial infection and identify which antibiotic to use if necessary.
• Hematology/serum biochemistry can identify/rule out conditions potentially responsible for polyuria.
• In cases of congenital UI, a karyotype should be performed, as UI has been reported in cases of XX-true hermaphroditism (ambiguous external genitalia) or female pseudohermaphroditism (male phenotype with XX karyotype). In bitches, even if the karytotype is normal (XX), a gonadotropin-releasing hormone agonist (GnRH) stimulation test (see Box) should be performed to rule out true hermaphroditism (presence of an ovotestis or 1 ovary and 1 testis) that might be responsible for congenital UI.

Postmortem Findings
• Gross necropsy findings may reveal ectopic ureters, bladder neoplasia, vaginal leiomyoma or leiomyosarcoma, transitional cell carcinoma of the urethra, persistent urachus, or an iatrogenic ureterovaginal fistula.
• In young animals or in congenital cases, ectopic ureters are most common, followed by anatomic abnormalities of the urogenital tract suggestive of an intersex condition (uterus masculinus, hypospadia, vaginal or vaginovestibular strictures, persistent hymen, ambiguous genitalia).
• Urethral mucosa may reveal atrophy in bitches with USMI, while bladder mucosa may reveal focal lymphocytic infiltration (lymphoid follicles) in chronic UTI.

Treatment

• Therapy of UI may be medical, surgical, or a combination of both.
Treatment of urinary incontinence will be discussed in Part 2 in an upcoming issue.

In General

Relative Cost
$ - $$$
The cost of diagnosing most UI cases is approximately $150 and includes complete physical examination, hematology and serum biochemistry values, and urinalysis. If further testing such as a UPP is performed, costs are increased (by $300 to $500).

Acknowledgement
The author wishes to thank Dr. Susi Arnold, University of Z¨urich, Switerland, for providing the figures in this article.


DIAGNOSING CANINE URINARY INCONTINENCE • Stefano Romagnoli

Suggested Reading
Association between urinary incontinence in bitches: Its incidence and relationship to neutering practices. Thrusfield MV. J Small Anim Pract 39:559-566, 1998.
Association in bitches between breed, size, neutering and docking, and acquired urinary incontinence due to incompetence of urethral sphincter mechanism. Holt PE, Thrusfield MV. Vet Rec 133:177-180, 1993.
Clinical and radiographic findings compared with urodynamic findings in neutered female dogs with refractory urinary incontinence. Nickel RF, Vink-Noteboom M, Van der Brom WE. Vet Rec 145:11-15, 1999.
Clinical response and urethral pressure profile changes after phenylpropanolamine in dogs with primary sphincter incompetence. Richter KP, Ling GV. JAVMA 187:605-611, 1985.
Colposuspension. Holt PE, Stone EA. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery, 4th ed-Philadelphia: Lippincott Williams & Wilkins, 1998, p 455.
Effect of a long acting GnRH analogue or placebo on plasma LH/FSH, urethral pressure profile and clinical signs of urinary incontinence due to sphincter mechanism incompetence in bitches. Reichler IM, Jochle W, Piché CA, et al. Theriogenology 66:1227-1236, 2006.
Evaluation of phenylpropanolamine in the treatment of urethral sphincter mechanism incompetence in the bitch. Scott L, Leddy M, Bernay F, et al. J Small Anim Pract 43:493-496, 2002.
Long-term risks and benefits of early-age gonadectomy in dogs. Spain CV, Scarlett JM, Houpt KA. JAVMA 224:380-387, 2004.
Pelvic bladder in dogs without urinary incontinence. Mahaffey MB, Barsanti JA, Barber DL, et al. JAVMA 184:1477-1479, 1984.
Pharmacokinetics of oestriol after repeated oral administration to dogs. Hoeijmakers M, Janszen B, Coert A, et al. Res Vet Sci 75:55-59, 2003.
Treatment of bitches with acquired urinary incontinence with estriol. Mandigers PJI, Nell T. Vet Rec 149:764-767, 2001.
Treatment of urethral sphincter mechanism incompetence in 11 bitches with a sustained-release formulation of phenylpropanolamine hydrochloride. Bacon NJ, Oni O, White RAS. Vet Rec 151:373-376, 2002.
Treatment of urinary incontinence in bitches by endoscopic injection of glutaraldehyde cross-linked collagen. Arnold S, Hubler M, Lott-Stolz GH, et al. J Small Anim Pract 37:163-168, 1996.
Urethral sphincter mechanism incompetence in male dogs: A retrospective analysis of 54 cases. Aaron A, Eggleton K, Power C, Holt PE. Vet Rec 139:542-546, 1996.
Urinary incontinence in the bitch due to sphincter mechanism incompetence: Prevalence in referred dogs and retrospective analysis of 60 cases. Holt PE. J Small Anim Pract 26:181-190, 1985.

Resources
www.icsoffice.org: The official site of the International Continence Society (a society for the study of human incontinence)

For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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