Urethral sphincter mechanism incompetence in spayed bitches: new insights into the pathophysiology and options for treatment.

Abstract

Incidence of USMI after ovariectomy Urinary incontinence is the involuntary loss of urine [1]. In intact bitches urinary incontinence is rare (0-1 %) [2], whereas in spayed bitches the incidence is up to 20% [3]. The underlying pathophysiological mechanism is mainly an acquired insuffi cient closure of the urethra after spaying [4]. Therefore urinary incontinence after spaying is called urethral sphincter mechanism incompetence (USMI). Within one year after spaying the urethral closure pressure is signifi cantly reduced. Because many bitches may only become incontinent years after surgery it took a long time until the causal relationship between ovariectomy and the occurrence of incontinence was proven [5]. In one study, 83 of 412 (20%) bitches became incontinent 3 to 10 years after surgery [3]. As long as 40 years ago urinary incontinence was described as a rare side effect of spaying [6]. However, it took 20 years to verify the causal relationship between the removal of the ovaries and urinary incontinence [5]. The triggering mechanism is still unclear. Neuronal damage can most likely be disregarded, as the risk of urinary incontinence is the same in ovariectomised and ovariohysterectomised bitches [3].