Ch 118 - USMI Flashcards

1
Q

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

A
  • 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)
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2
Q

What is the role of the pudendal nerve in continence?

A

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

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3
Q

List potential causes of congenital USMI?

A
  • Abnormally short or absent urethra (esp. cats)
  • Diverticula and dilations in juvenile male dogs
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4
Q

What factors are known or suspected to contribute to USMI?

A
  • 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
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5
Q

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

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

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

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6
Q

How does gonadectomy predispose to the development of USMI?

A
  • 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

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7
Q

How do hormones effect USMI?

A
  • 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
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8
Q

How is USMI diagnosed?

A

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

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9
Q

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

A

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

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10
Q

When are estrogens contraindicated in the treatment of USMI?

A

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

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11
Q

List the main surgical options for USMI:

A
  • Colposuspension
  • Urethropexy
  • Cystourethropexy
  • Bulking agents (submucosal bovine cross-linked collagen)
  • Transpelvic urethral sling
  • Transobturator vaginal tape
  • Artificial urethral sphincter
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12
Q

What vessels need to be identified and avoided during colposuspenstion?

A

External pudendal vessels

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13
Q

What is the prognosis after colposuspension?

A
  • 53-55% complete continence
  • Recurrence in approx 11%
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14
Q

What is the expected outcome with urethropexy?
Cystourethropexy?

A

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

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15
Q

What options are there for bulking agents?

A

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

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16
Q

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

A
  • 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
17
Q

What is the prognosis with a transpelvic urethral sling?

A
  • 6/13 fully continent long term
  • Combined with colposuspension - 7/12
18
Q

What is the reported outcome of transobturator vaginal tape?

A
  • 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
19
Q

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

A
  • Female: At least 2cm caudal to bladder neck to avoid impedence of the ureters
  • Male: 1cm caudal to prostate
20
Q

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

A
  • 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)
21
Q

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

A
  • 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%
22
Q

How does treatment of USMI in male dogs differ?

A
  • 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