Urethral Sphincter Mechanism Incompetence (USMI)

Critical history, blood tests and urinalysis: Urinary incontinence is a common reason for presentation, particularly in neutered bitches. It is however, important to distinguish incontinence from pollakiuria, polyuria and behavioural problems. This necessitates asking the client the right questions, performing a thorough physical examination, and sometimes checking urine specific gravity. It is useful to establish the timing of the episodes, volume of urine passed and events surrounding the leakage of urine. Animals with incontinence usually present with intermittent or continuous dribbling of urine but can void normally. Potential causes of urinary incontinence include urethral sphincter mechanism incompetence (USMI), ectopic ureters, neurological abnormalities, detrusor instability and genitourinary tract neoplasia. When incontinence is confirmed, a thorough history, physical examination, neurological examination, urinalysis and aerobic urine culture should be performed. Due to the high prevalence of USMI in adult, neutered bitches and the low cost and risk of treatment, if the results of these steps are consistent, alpha-agonists or estrodiol are frequently trialled prior to further investigations. If the presumptive diagnosis is correct, this treatment is often effective. If not or if the animal does not fit these criteria, further investigations including a complete blood count, biochemistry and abdominal imaging are required to establish the diagnosis.

Imaging the urogenital tract: what test when? Diagnostic imaging can be a very powerful tool in the investigation of urogenital disease, with the differing modalities having strengths and weaknesses for the different areas of the tract. Generally, ultrasound would be recommended as the most appropriate first-line investigation for most structures in the urogenital tract, allowing clear visualisation of the internal structure of the kidneys and reproductive structures (ovaries, uterus, prostate, testes). Radiography may allow diagnosis of altered shape or size of these structures but the changes seen are usually less specific than those that can be identified with ultrasound. Ultrasound and/or contrast radiography can be used for assessment of the bladder (with ultrasound usually being more convenient (and allowing guided cystocentesis if required), but care must be taken in interpretation of the bladder wall if the bladder is not particularly distended. For the ureters and urethra, positive contrast radiography (Intravenous urography, retrograde (vagino) urethrography) often allows clearer assessment of the length of these structures. If available, Computed Tomography can be particularly useful for the assessment of ureteric anatomy (e.g. for aberrant insertion/ectopia). In many cases, multi-modality imaging may be appropriate, particularly if investigation for changes in other body areas is required (e.g. metastatic spread from a neoplastic process).