Quarterly Newsletter

2013-Oct-IVGNewsletter-InternalMedicine

The IVG Hospitals Quarterly Veterinary Newsletter features articles of interest to the veterinary medical community, written by veterinarians and veterinary specialists at our four locations.

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Urinary Incontinence URINARY INCONTINENCE (UI) OF A BELOVED, indoor pet can cause a significant amount of anxiety in a family due to soiling of carpeting and furniture. This condition can even lead to quality of life dilemmas for pet owners. Urinary incontinence is defined as loss of voluntary control of urination, resulting in leakage of urine from the urinary system to the exterior of the body. While UI has consequences for our clients' homes, it can also cause significant pathology to our patients. Timely diagnosis and control of this potentially chronic problem will help to ameliorate these concerns. PHYSIOLOGY OF MICTURITION A basic understanding of urinary bladder and urethral function can help to guide diagnosis and treatment for disorders of micturition, including UI. Urethral sphincter function is responsible for urine retention, and sphincter relaxation results in micturition. Dogs have a functional internal urethral sphincter, which is involuntary, and a true external urethral sphincter, which is under voluntary control. The muscles of the pelvic floor contribute to voluntary urine retention. During normal urine storage the sympathetic nervous system predominates. The hypogastric nerve relaxes the detrusor muscle via -adrenergic stimulation. While the urinary bladder is relaxed, urine is collected and stored against a contracted internal urethral sphincter. The internal urethral sphincter is made up of the contracted smooth muscle of the bladder neck and urethra, which undergoes α-adrenergic stimulation from the hypogastric nerve. Voluntary contraction of the external urethral sphincter contributes to increased urethral resistance and helps to maintain continence. During the voiding phase parasympathetic tone predominates. The stretch receptors of the urinary bladder send signals to the brain, which results in cholinergic stimulation of the detrusor muscle causing contraction with concomitant relaxation of the internal urethral sphincter. With voluntary Annalisa Prahl, DVM, DACVIM Annalisa Prahl, DVM, DACVIM practices at Bulger Veterinary Hospital in North Andover, MA. relaxation of the external urethral sphincter and the muscles of the pelvic floor, normal voiding occurs and the bladder returns to a relaxed state. APPROACH TO DIAGNOSIS AND ASSESSMENT OF URINARY INCONTINENCE The owner's impression and description of the micturition problem is the first step in a diagnosis of UI. Appropriate questions should be asked to ascertain when the urinary incontinence began, whether it occurs only when recumbent or sleeping or if the UI occurs during exercise and normal behavior. It is also important to determine if the UI occurs before or after voiding. The three most common differential diagnoses of UI include urethral incompetence, ectopic ureters, and neurologic disorders. Acquired Urethral Sphincter Mechanism Incompetence (USMI) is typically seen in medium to large breed dogs months to years after ovariohysterectomy. Incontinence often occurs at night or while recumbent and is only intermittent. The volume of urine lost can vary from small drops to large puddles. The exact cause of USMI is not completely understood. Theories include: aging, a relative lack of estrogen, which may affect the urethral responsiveness to adrenergic stimulation, decreases in the length of the urethra, and changes in concentration of gonadotropin releasing hormone. Congenital urethral incompetence is typically seen |1|

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