Page 764 - Small Animal Internal Medicine, 6th Edition

736 PART V Urinary Tract Disorders

urethral stents if needed (Video 45.5). If no mechanical urethral sphincter. Prazosin is much more cost-effective that
obstructions are present, urodynamic studies may help phenoxybenzamine, another α-antagonist, particularly
VetBooks.ir provide insight for functional obstructions, but oftentimes when used in larger-breed dogs. More selective α 1 -
antagonists, such as tamsulosin (Flomax), have been used
the increased urethral pressure may only occur during the
act of micturition. The diagnosis of idiopathic functional
with variable and better results for DUD. In some cases, a
urethral outflow tract obstruction (detrusor-urethral dys- anecdotally for functional urethral outflow obstructions,
synergia [DUD]) is usually made when all other causes for skeletal muscle relaxant such as diazepam is also beneficial.
the increased urethral closure pressure have been excluded. Once these drugs have taken effect, or a urinary catheter is
This disease usually occurs in large-breed male dogs, both in place, parasympathomimetics can be started if secondary
castrated or intact. bladder atony is also present. Bethanechol, a muscarinic
Treatment for mechanical obstructions is to remove the agent, might help restore bladder tone and facilitate bladder
obstruction, if possible. Urethral stones can be removed via emptying. In severe cases, a tube cystotomy, indwelling
surgery or holmium:YAG laser lithotripsy. Bladder and ure- urinary catheter, or urethral stent (Fig. 45.6) may be needed
thral neoplasia, usually transitional cell carcinoma (TCC; for urine evacuation.
Fig. 45.5), should be treated with piroxicam or another
nonsteroidal antiinflammatory drug (NSAID); other chemo- Overactive Bladder
therapeutics such as mitoxantrone or platinum compounds Animals that present with pollakiuria may have an overac-
may improve survival. Proliferative urethritis is usually seen tive bladder (OAB), which results in urge incontinence.
in female dogs and may result from chronic UTIs. More Usually animals with OAB have underlying cystitis caused
recent unpublished data suggests that deep-seated UTIs may by bacteria, cystic calculi, neoplasia, polyps, or drugs (e.g.,
be associated with some of these cases, and fluorescent in cyclophosphamide). A detailed history is necessary to docu-
situ hybridization (FISH) studies can be submitted if ure- ment whether other lower urinary tract signs are present.
thral biopsies are obtained. Cystoscopically, proliferative Physical examination of animals with pollakiuria is generally
urethritis appears as multiple frond-like pieces of tissue in unremarkable; the bladder is usually small on palpation. In
the urethral lumen that can be very dense and cause ure- some dogs and cats, masses or numerous cystic calculi may
thral obstruction. A biopsy is necessary to differentiate this be palpable, if present. A urinalysis should be performed and
from TCC. In addition to proper antimicrobials, NSAID a urine culture should be evaluated. If the culture is negative
therapy has been reported to help manage this disease. In and clinical signs persist, further diagnostic studies such as
one case study, azathioprine was also reported to be effective. abdominal ultrasonography and radiography are indicated.
If urethral obstruction occurs, urethral stenting should be If an underlying cause for the clinical signs is not found,
considered. referral for a cystometrogram and advanced imaging may be
For idiopathic, functional, urethral outflow tract obstruc- considered.
tion, α 1 -adrenoceptor antagonists such as prazosin can be Occasionally idiopathic OAB (iOAB) is thought to occur
used to help decreased the closure pressure of the internal and medical treatment may be beneficial for controlling

0

1
+
2
U BLADDER
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3

4
1.58 cm

FIG 45.5
An ultrasonographic image from an 11-year-old female FIG 45.6
spayed Brittany Spaniel Mix that presented for stranguria Later radiograph of a 1.5-year-old male, castrated domestic
and urinary incontinence. A urethral mass is noted that shorthair that presented for a urethral stricture secondary to
extends into the bladder lumen (arrow). Fine-needle trauma. After the stricture was ballooned, a urethral stent
aspiration confirmed this mass to be a transitional cell (arrow) was placed. Because of concern for bladder atony,
carcinoma. In addition to piroxicam therapy, a urethral stent the parasympathomimetic bethanechol was also
was placed in this dog. administered.