Management of Urinary Incontinence Managing Urinary Incontinence

Management of Urinary Incontinence
Sheri J. Ross, BSc, DVM, PhD, Dipl. ACVIM (Internal Medicine)
Managing Urinary Incontinence
Urinary incontinence is very prevalent among older animals. In this group of animals it is
important to consider the impact of non-urinary conditions as well. Correct identification
of the underlying cause and aggressive management may improve the quality of life for
both the patient and owner.
Micturition is the act of urination and includes both a storage phase and a voiding phase.
Animals presenting with urinary incontinence typically have one or more problems with
the storage phase of micturition, which can usually be categorized as; insufficient
urethral closure pressure; failure of the bladder to relax and accommodate urine; or
abnormal anatomy of the bladder, ureter(s) and/or urethra.
Pathophysiology
The main organs involved in urination are the bladder and the urethra. The smooth
muscle of the bladder, known as the detrusor muscle, is innervated by sympathetic
nerve fibers from the lumbar spinal cord and parasympathetic fibers from the sacral
spinal cord. The internal urethral sphincter consists of smooth muscle bundles that pass
on either side of the urethra. More distal along the urethra is the external urethral
sphincter which is composed of skeletal muscle and is innervated by the somatic
pudendal nerve which originates in Onuf's nucleus in the cord.
In healthy animals, the lower urinary tract has two discrete phases: the storage phase
and the voiding phase. The muscles controlling micturition are controlled by both the
autonomic and somatic nervous systems.
Storage phase
During the storage phase the internal urethral sphincter remains tense and the detrusor
muscle relaxed by sympathetic stimulation. The storage phase is controlled via
stimulation of beta receptors in the bladder wall; causing detrusor muscle relaxation and
alpha-1 receptors in the proximal urethra; causing urethral contraction. Sympathetic
(adrenergic) input from the hypogastric nerve regulates the stimulation of these
receptors. Skeletal muscle in the more distal urethra also contributes to urethral closure
pressure and continence. This skeletal muscle is under voluntary control and is
innervated by the somatic nervous system, principally through the pudendal nerve.
Stimulation of the pudendal nerve with the neurotransmitters norepinephrine (NE) and
serotonin (5-HT) results in contraction of the striated component of the urethral
sphincter.
Voiding phase
During voiding, parasympathetic stimulation causes the detrusor muscle to contract and
the internal urethral sphincter to relax. As the bladder fills, sensory receptors in the
bladder wall ascend the spinal cord to both the pontine micturition center and the
cerebrum transmit the need to urinate. Once the voluntary signal to begin voiding has
been issued, neurons in pontine micturition center fire maximally, causing excitation of
sacral preganglionic neurons. The firing of these neurons results in contraction of the
detrusor muscle and expulsion of urine from the bladder. The pontine micturition center
also causes inhibition of Onuf's nucleus, resulting in relaxation of the external urinary
sphincter. Under parasympathetic (cholinergic) control via the pelvic nerve, alphaadrenergic input to the bladder neck and proximal urethra is inhibited resulting in
relaxation.
Mechanism of storage and voiding reflexes. A. Storage reflexes. B. Voiding reflexes.
(From Chancellor MB, Yoshimura N: Physiology and pharmacology of the bladder and
urethra. In Walsh PC (ed): Campbell's Urology, pp 831–886. Philadelphia, Saunders,
2002).
Urethral sphincter mechanism incompetence
In canines, incontinence is most often a result of inadequate urethral closure pressure.
Urethral sphincter mechanism incompetence (USMI) is also known as "spay
incontinence" or "hormone responsive incontinence". USMI is very common occurring in
up to 30% of spayed dogs; most frequently in young to middle-aged, larger-breed dogs
that have been spayed in the past 4 years. Factors contributing to the development of
USMI may include an age related decline in collagenous support structures around the
urethra and/or a decrease in sensitivity of adrenergic receptors within the urethra. An
abnormally positioned bladder, obesity and anatomic abnormalities in the vagina and
vestibule may also contribute to the problem. Although much more common in females,
USMI may occur in males as well.
Medical Management of Incontinence
Alpha-Adrenergic Agonists - Alpha-adrenergic agonists are one of the more common
groups of drugs used in the management of canine urinary incontinence. These
medications increase urethral tone my acting on the muscle in the urethral wall. The
usual medication for canine use is phenylpropanolamine (Proin®) and is typically given
two or three times daily. Increased blood pressure and behavioural changes are the
most commonly observed side effects. Other side effects may include a decrease in
appetite and irritability. Most dogs tend to tolerate phenylpropanolamine quite well and
side effects are not common. It is important to monitor blood pressure periodically and to
use with caution in patients with heart disease.
There is a sustained release version of phenylpropanolamine available called
cystolamine. This medication maintains a more stable blood concentration that does
phenylpropanolamine and is thus more effective at controlling incontinence.
Unfortunately this medication has been on indefinite “back-order” in the United States
and Canada for the past 2 years.
Estrogens - Estrogens are used to manage incontinence in post-menopausal women as
well as dogs. Many dogs develop incontinence after being spayed due to the decrease
in estrogen in their systems. Estrogens have also been helpful in managing incontinence
from other causes as well. In dogs, DES (diethylstilbestrol) is the most common
estrogen used, though it is now only available through compounding pharmacies.
Typically, the patient is treated daily for 5 days and then the dosage is decreased to 1-2
times a week. Once continence has been attained, the frequency of dosing should be
reduced the lowest possible dosage that will control the clinical signs. Although much
less common with the newer estrogens such as DES, side effects are still possible and
include bone marrow blood problems and hair loss. Side effects are more common in
older animals and with high dosages. To monitor for any bone marrow problems, regular
bloodwork is recommended. Proin and DES are often used in combination, and seem to
be synergistic.
Non-medical treatments
Although medications or combinations of medications work for most patients to control
the incontinence, if the leaking is not controlled there are surgical options to consider:
colposuspension and/or urethropexy and collagen injections.
Colposuspension/Urethropexy: is the most commonly performed procedure in
females. Here, the vagina is tacked to the ventral wall entrapping and compressing the
urethra. Fibers from the urethral muscles can also be tacked down to increase the
tension and hopefully improve urethral tone. Medications listed above are used in
conjunction with surgery. After urethropexy, 56% of affected dogs were continent and
27% had improvement of incontinence. A similar success rate was observed after
colposuspension, with 53% of the female dogs continent and 38% with marked
improvement.
Hydraulic Occluder Cuff: Another option for controlling incontinence is the placement
of a hydrolic occlude cuff around the trigone and proximal urethral. This cuff is placed
surgically and, after the patient has healed from surgery, is inflated to an appropriate
pressure to prevent leakage, but still permitting conscious urination.
Urethral Collagen Injections: Another option for the management of refractory
incontinence is the injection of collagen into the urethra to decrease the luminal diameter
and thus decrease leaking. Collagen injections are also useful in managing incontinence
in cases where the patient can not be treated with the medications described above due
to other medical conditions. Due to technical and size limitations, the cystoscopic
method of collagen delivery is only appropriate for medium to larger female dogs. For
smaller females and males, the collagen must be delivered via surgery or laparoscopy
so that the urethra may be visualized. The most recent data suggest that approximately
68% of treated dogs will regain continence, although most still require medical therapy
as well. The average duration of continence following collagen injections is reported to
be 17 months with a range of 1-64 months. As the collagen tends to “flatten” with time,
the injections may need to be repeated. At present, there is no data describing the
success of repeated collagen injections, but we suspect that the success rate will be
slightly lower due to scarring and difficulty with placement of the new injections. Collagen
injection compares well to established surgical methods for treatment of refractory
incontinence and is much less invasive.
Table 1. Common Causes of Urinary Incontinence
Non-neurogenic causes
 Urethral sphincter mechanism incompetence
 Detrusor hyper/hypocontractility
 Inflammation of the bladder or urethra
 urinary tract infction
 uroliths
 neoplasia
 Anatomic abnormalities
 ectopic ureters
 pelvic bladder
 vestibulovaginal malformations
Neurogenic causes
 Trauma or spinal lesion
 FeLV (cats)
 Dysautonomia
 Increased urethral tone
 reflex dyssynergia
 upper motor neuron bladder
 Congenital (Manx cats)
Table 2. Some Useful Drugs in the Management of Canine Urinary Incontinence
Agent
Phenylpropanolamine
Classification
Alpha agonist
Recommended Dosage (Dogs)
1.5 mg/kg PO q 8 - 12 hrs
Cystolamine
(sustained release
phenylpropanolamine) – no longer
available in North America
Diethylstilbestrol (DES)
Imipramine
Oxybutynin
Alpha agonist
1-2 mg/kg PO q 24 hrs
Reproductive
hormone
Antimuscarinic,
alpha/beta agonist
Antimuscarinic
0.1 - 1.0 mg/dog PO q 24 hrs for 5 7 days, then weekly or as needed
5 - 15 mg PO q 12 hrs
0.2 mg/kg PO q 8 - 12 hrs
Cats/small dogs: 0.5-1.25 mg total
dose
Larger dogs: 2.5 – 3.75 mg total
dose