Normal urinary continence
Micturition may be defined as function of the lower urinary tract that encompasses both a storage phase and a voiding phase.
During the storage phase of micturition, the urinary bladder, acting as a low-pressure reservoir, is relaxed and fills with
urine. Even though pressure in the urinary bladder gradually increases, urine remains contained within the bladder lumen because
of resistance generated primarily by smooth muscle in the bladder neck and striated muscle in the urethra which function as
high-pressure, unidirectional valves.
Low pressure in the bladder lumen is maintained by activity in beta-adrenergic (sympathetic) receptors via the hypogastric
nerve and central inhibition of cholinergic (parasympathetic) activity. High pressure in the bladder neck and preprostatic
urethra is maintained primarily by activity of alpha-adrenergic (sympathetic) receptors via the hypogastric nerve.
High pressure in the postprostatic urethra is sustained primarily by skeletal (urethralis) muscle activated by the pudental
During the voiding phase of micturition, the parasympathetic innervation (via the pelvic nerve) of the bladder muscle (detrusor
muscle) is activated. As a result of contraction of the detrusor muscle, the bladder becomes a high-pressure pump, expelling
urine through the urethral lumen. Simultaneously, the urethra becomes a low-pressure conduit for urine being voided from the
bladder because of inhibition of alpha adrenergic innervation to smooth muscle of the bladder neck and urethra, and inhibition
of innervation to the striated urethralis muscle.
Urinary incontinence defined
Urinary incontinence is defined as involuntary leakage of urine. Therefore, it is different from behavioral periuria characterized by normal voluntary
elimination of urine in the wrong place (sites other than the litter box or outdoors) or the wrong time (nocturia) as defined
by the owner. There are a variety of types of urinary incontinence.
Urge incontinence is defined as frequent uncontrollable contraction of the detrusor muscle when the bladder is minimally distended with urine.
It is intermittent in nature, and is often associated with pollakiuria, dysuria and sometimes hematuria. It is typically associated
with inflammation of the lower urinary tract. Urge incontinence may also be associated with reduced bladder capacity secondary
to diffuse neoplasia of the bladder wall, chronic inflammatory fibrosis of the bladder wall or partial cystectomy. Refer to
the sections on bacteria UTI and neoplasia for additional information.
Urethral sphincter incompetence may result in urinary incontinence due to decreased urethral tone during the storage phase of micturition. Incontinence may
be more noticeable during periods of rest, or during events associated with increased abdominal pressure such as coughing.
It may also develop or become more evident if the patient develops polyuria. Incontinence due to urethral sphincter incompetence
is often an exclusion diagnosis.
Overflow incontinence is a type of neurogenic incontinence associated with impaired detrusor muscle function such that the bladder lumen continues
to fill until intravesicular pressure exceeds urethral resistance. With lower motor neuron disorders involving sphincters,
overflow of urine into the urethra occurs at low intravesicular pressures. In contrast, with upper motor neuron disorders,
incontinence occurs at higher intravesicular pressures due to reflex sphincter resistance.
Paradoxical incontinence occurs when mechanical (e.g. uroliths or urethral plug) or functional (e.g. reflex dyssynergia) obstruction of the urethra
impairs the voiding phase of micturition. When intravesicular pressure exceeds the pressure at the site(s) of urethral obstruction,
urine escapes around the obstruction through the remaining unobstructed portions of the urethra. The name paradoxical incontinence
is derived from the fact that incontinence occurs in association with obstruction.
Urinary incontinence diagnosis
Most causes of urinary incontinence may be classified as disorders of the storage phase of micturition. The exception is overflow
(including paradoxical) urinary incontinence, which is a disorder of the voiding phase of micturition. Urinary incontinence
may be: 1) congenital or acquired, 2) neurogenic or non-neurogenic, and 3) constant or intermittent.
See Table 1 for suggestions regarding the initial diagnostic evaluation of patients with urinary incontinence. In some patients,
a functional diagnosis may require urodynamic studies, including cystometry, urethral pressure measurements and electromyography.
Even then, the underlying cause may not be detected.
Drugs used for symptomatic treatment
Although frequently cited in textbooks, the safety and efficacy of many drugs commonly used to treat urinary incontinence
and other disorders of micturition in cats have not been evaluated by blinded controlled clinical trials using patients with
naturally occurring disease (Table 2, p. 8S). Many dosages have been extrapolated from recommendations derived for other species
and personal experience.
Therefore, they should be used only after informed consent of clients and with compassionate precautions. This includes review
of the manufacturer's description of indications, contraindications, adverse events and contacting the manufacturer for additional
information about unpublished studies in the feline species.
If significant side effects are associated with use of these drugs, then they may be minimized by reducing the dose and/or
frequency of administration. In this context client education is important. Undesirable side effects are often associated
with less frustration if clients can 1) anticipate them, 2) recognize the difference between nuisance side effects and significant
adverse reactions, and 3) be taught how to deal with them if they occur.