USMI Flashcards
What are the (4) interacting mechanisms which are responsible for maintaining urinary continence?
- 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)
What is the role of the pudendal nerve in continence?
Contracts striated muscle of the external urethral sphincter for voluntary control of micturition.
List potential causes of congenital USMI?
- Abnormally short or absent urethra (esp. cats)
- Diverticula and dilations in juvenile male dogs
What factors are known or suspected to contribute to USMI?
- 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
What breeds are overrepresented with USMI?
How much more likely is USMI to occur in large/giant breeds?
- Old English Sheepdog
- Doberman
- Rottweiler
- Weimeraner
- Irish Setters
Large- and giant-breed dogs are 7x more likely to develop USMI
How does gonadectomy predispose to the development of USMI?
- 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
How do hormones effect USMI?
- 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
How is USMI diagnosed?
Mostly a diagnosis of exclusion. Need to rule out other causes of incontinence such as ectopic ureters or conformational abnormalities causing overflow (recessed vulva)
List the (3) main options for medical management of USMI:
What is the rate of single-therapy resulting in cure of incontinence?
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
When are estrogens contraindicated in the treatment of USMI?
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
List the main surgical options for USMI:
- Colposuspension
- Urethropexy
- Cystourethropexy
- Bulking agents (submucosal bovine cross-linked collagen)
- Transpelvic urethral sling
- Transobturator vaginal tape
- Artificial urethral sphincter
What vessels need to be identified and avoided during colposuspenstion?
External pudendal vessels
What is the prognosis after colposuspension?
- 53-55% complete continence
- Recurrence in approx 11%
What is the expected outcome with urethropexy?
Cystourethropexy?
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
What options are there for bulking agents?
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
What location is recommended for injection of bovine cross-linked collagen?
- 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
What is the prognosis with a transpelvic urethral sling?
- 6/13 fully continent long term
- Combined with colposuspension - 7/12
What is the reported outcome of transobturator vaginal tape?
- 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
Where is the recommended location of an artificial urethral sphincter in female and male dogs?
- Female: At least 2cm caudal to bladder neck to avoid impedence of the ureters
- Male: 1cm caudal to prostate
How do you measure for sizing of a artifical urethral sphincter?
- 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)
What % or dogs are expected to be continent without inflation of the artifical sphincter?
What are the general rules of cuff inflation?
- 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%
How does treatment of USMI in male dogs differ?
- 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
