Urinary incontinence in dogs -- diagnosis and treatment (Proceedings)


Urinary incontinence in dogs -- diagnosis and treatment (Proceedings)

Primary sphincter mechanism incompetence (PSMI)

PSMI (idiopathic incontinence, hormone-responsive incontinence) is the most common and important acquired cause of incontinence in dogs. It largely is a condition of spayed female dogs, but in some breeds incontinence may precede ovariohysterectomy (OHE). Decreases in maximal urethral closure pressure and functional urethral length predictably occur during the first 12 to 18 months after spaying, resulting in a caudal shift of the urethral profile, and a deterioration of urethral closure function. It is speculated that this decline in urethral closure pressure continues with advancing age.

Approximately 20% of female dogs will develop PSMI a mean of 2.9 years after OHE performed after their first heat (immediately to 12 years later). Dogs greater than 20 kg (31%) are more likely to develop PSMI than are those less than 20 kg (9.3%). Incontinence is about one-half as frequent in bitches that undergo OHE before their first heat, but episodes of incontinence are worse. In one study, early-age gonadectomy was associated with an increased rate of urinary incontinence prompting the recommendation that gonadectomy should be delayed until at least 3 months of age. In another study, female dogs neutered at 7 weeks of age did not have increased urinary incontinence compared to those neutered at 7 months of age. Boxers in Europe comprise 65% of cases whereas Dobermans and Giant Schnauzers predominate in the USA. Confirmation of the diagnosis of PSMI is made by finding low maximal urethral closure pressure and decreased functional profile length during urethral pressure studies.

Phenylpropanolamine (PPA) at 1.0 to 1.5 mg/kg PO BID to TID effectively controls incontinence in about 74 to 92% of dogs with PSMI by stimulating alpha-adrenoreceptors in the urethra and increasing urethral tone. Of those not completely continent following PPA, many will have some improvement in their {Kyles, 1998 #6}continence. OVER HALF of dogs treated with regular PPA that failed to respond, became continent when treated with sustained release PPA. The effect of PPA to control continence becomes less over time in some dogs. PPA sometimes must be given two to three times per day to control incontinence. Not all alpha agonists have the same effect as PPA had a greater effect than pseudoephedrine in a recent study. If incontinence only occurs during the sleeping hours, the highest dose can be given before bedtime. Rarely, some dogs display restlessness and mild behavioral changes on PPA which makes its use less attractive. The beneficial effect of alpha-adrenoreceptor stimulation appears to be greatest in dogs that were older and had OHE performed long before incontinence started. Dogs with systemic hypertension should not be treated with alpha-adrenergic agents that could aggravate their systemic hypertension. Similarly, dogs with clinically relevant cardiac or renal disease should not be treated with alpha-adrenergic agonists. Systemic blood pressure should be measured at baseline, one week, 1 month and at 3 months to ensure that hypertension is not emerging. Twice yearly measurements of systemic blood pressure are recommended thereafter.