Ch 118 - USMI

Question 1

What are the (4) interacting mechanisms which are responsible for maintaining urinary continence?

Answer 1

• Urethral smooth muscle (most prevalent in the cranial 1/2 of the urethra)
• Striated muscle (urethral “sling” in caudal third of the urethra)
• Natural elasticity of the urethral wall
• Physical properties of the urethra (length and diameter, pelvic diaphragm muscle mass)

Question 2

What is the role of the pudendal nerve in continence?

Answer 2

Contracts striated muscle of the external urethral sphincter for voluntary control of micturition.

Question 3

List potential causes of congenital USMI?

Answer 3

• Abnormally short or absent urethra (esp. cats)
• Diverticula and dilations in juvenile male dogs

Question 4

What factors are known or suspected to contribute to USMI?

Answer 4

• Urethral tone
• Tail docking (through reduction in pelvic diaphragm mass)
• Urethral length
• Bladder neck position (changes in conveyance of abdominal pressure to the urethra)
• Body size and breed
• Gonadectomy
• Hormones

Question 5

What breeds are overrepresented with USMI?
How much more likely is USMI to occur in large/giant breeds?

Answer 5

• Old English Sheepdog
• Doberman
• Rottweiler
• Weimeraner
• Irish Setters

Large- and giant-breed dogs are 7x more likely to develop USMI

Question 6

How does gonadectomy predispose to the development of USMI?

Answer 6

• Results in significantly higher proportion of collagen and lower proportion of muscle in the lower urinary tract. (Female urethra is already about 75% collagen)
  -Possibly through urothelium/urethral lining atrophy from lack of estrogen

Risk of developing incontinence is 8x higher in spayed females

Question 7

How do hormones effect USMI?

Answer 7

• Lack of estrogen results in reduction of smooth muscle tone
• Gonadectomy may also reduce the numbers of muscle fibers of the striated urethralis muscle
• Increase in gonadotropins LH and FSH leads to lower expression of COX-2 and its m-RNA, leading to decreased prostaglandins in the lower urinary tract

Question 8

How is USMI diagnosed?

Answer 8

Mostly a diagnosis of exclusion. Need to rule out other causes of incontinence such as ectopic ureters or conformational abnormalities causing overflow (recessed vulva)

Question 9

List the (3) main options for medical management of USMI:
What is the rate of single-therapy resulting in cure of incontinence?

Answer 9

Phenylpropanolamine (Proin)- alpha adrenergic agonist
Estrogens (DES) - Improve smooth muscle contractility and sensitivity to alpha-adrenergic stimulation
GnRH analogs - decrease pituitary release of LH and FSH. Action suspected to be mainly on bladder function

50% of dogs will be cured with single therapy treatment

Question 10

When are estrogens contraindicated in the treatment of USMI?

Answer 10

Prior to the first estrus
- About 50% of dogs will have their incontinence resolve after the first estrus
- Contraindicated before due to potential adverse feedback on the pituitary

Question 11

List the main surgical options for USMI:

Answer 11

• Colposuspension
• Urethropexy
• Cystourethropexy
• Bulking agents (submucosal bovine cross-linked collagen)
• Transpelvic urethral sling
• Transobturator vaginal tape
• Artificial urethral sphincter

Question 12

What vessels need to be identified and avoided during colposuspenstion?

Answer 12

External pudendal vessels

Question 13

What is the prognosis after colposuspension?

Answer 13

• 53-55% complete continence
• Recurrence in approx 11%

Question 14

What is the expected outcome with urethropexy?
Cystourethropexy?

Answer 14

Urethropexy:
- 56% completely continent
- Of dogs whi failed to respond, an additional urethropext resulted in cure in 53%
- Combined with colposuspenstion - 70% cure

Cystourethropexy (6-10 horizontal mattress sutures)
- 2/10 completely cures, and additional 2 improved

Question 15

What options are there for bulking agents?

Answer 15

Teflon
- original materail described, 77% success
- Assoc with peritoneal granuloma formation

Bovine cross-linked collagen
- now the preferred material but only 53% success

Polyethylene glycol carboxymethyl cellulose hydrogel
- Resulted in granulomatous, FB reaction, significantly greater inflammation and mucosal erosions in some dogs

Question 16

What location is recommended for injection of bovine cross-linked collagen?

Answer 16

• Immediately below the mucosa, 1.5-2cm caudal to the vesicourethral junction
• Repeated circumferentially until injection sites appose one another - most dogs need three injections

Question 17

What is the prognosis with a transpelvic urethral sling?

Answer 17

• 6/13 fully continent long term
• Combined with colposuspension - 7/12

Question 18

What is the reported outcome of transobturator vaginal tape?

Answer 18

• complete continent in 92-100% in short term
• Long term: 3/12 completely continent, 3/12 improved, 3/12 incontinent episodes 1+ times a month

Question 19

Where is the recommended location of an artificial urethral sphincter in female and male dogs?

Answer 19

• Female: At least 2cm caudal to bladder neck to avoid impedence of the ureters
• Male: 1cm caudal to prostate

Question 20

How do you measure for sizing of a artifical urethral sphincter?

Answer 20

• Meaure the circumference of the urethra in surgery with suture or a penrose drain.
• Appropriate sphincter size estimated to be 50% of the circumference
• Most commonly used sized are 8,10,12mm (6-16mm available) with a cuff width of 14mm (available in 11 or 14mm)

Question 21

What % or dogs are expected to be continent without inflation of the artifical sphincter?
What are the general rules of cuff inflation?

Answer 21

• 33-45% continent with uninflated cuff
• Must wait 6 weeks prior to inflation to allow resolution of inflammation and revascularisation of dissected urethra
• Inj 0.05-0.2ml sterile saline at weekly or monthly intervals
• Complete continence 36-56%
• Obstruction in 7-17%

Question 22

How does treatment of USMI in male dogs differ?

Answer 22

• Less responsive to medical management
• Most responsive to alpha-adrenergics
• Vas deferensopexy and prostatopext have been reported
• Artificial sphincter placement in three dogs and appears to be effective