Urinary retention can present as urinary incontinence. Mechanical causes for urinary retention include urethroliths, urinary
bladder and/or urethral neoplasia, proliferative urethritis, urethral strictures, urethral foreign bodies, urethral plugs
in cats, prostatic diseases (abscess, paraprostatic cyst, benign prostatic hypertrophy) and extraluminal compressions. Functional
obstructions can be seen with suprasacral or brainstem disease (upper motor neuron bladders), urethral spasms that usually
occur secondary to urethritis or a mechanical obstruction, idiopathic detrusor-urethral dyssynergia, and administration of
phenylpropanolamine. Urinary bladder dysfunction can lead to detrusor atony and secondary overflow incontinence. Urinary bladder
dysfunction can occur secondary to a prolonged obstruction (functional or mechanical), neurogenic causes (sacral cord lesions,
pelvic nerve injuries, peripheral neuropathy), pharmacologic agents (anticholinergics, tricyclic antidepressants, opioids)
or be idiopathic.
The diagnosis of overflow incontinence is made based on history, thorough physical and neurologic examination and thorough
imaging of the urinary tract. Survey radiographs, cystourethrograms and cystoscopy can all be beneficial to evaluate the dog
for mechanical obstructions. An enema should be performed prior to radiographic studies in order to fully evaluate the distal
urethra. Cystoscopy is useful to evaluate the urethral mucosa and obtain samples for biopsy and culture. If no mechanical
obstructions are present, urodynamic studies can help provide insight for functional obstructions and may even be able to
help localize the area of injury.
Treatment for mechanical obstructions is to remove the obstruction if possible or treat the lesion pharmacologically (e.g.,
piroxicam for neoplastic disorders or proliferative urethritis). Secondary medications may still be warranted if urethral
spasticity occurs. Alpha-1 adrenoceptor antagonists (phenoxybenzamine, prazosin) can be used to help relax the internal urethral
sphincter. In some cases, such as reflex dyssynergia, a skeletal muscle relaxant such as valium is also beneficial. Once these
drugs have taken effect or a urinary catheter is in place, parasympathomimetics can be started. Bethanechol, a muscarinic
agent, helps to restore urinary bladder tone and facilitate urinary bladder emptying.
An overactive urinary bladder occasionally results in urinary incontinence, although more commonly it causes pollakiuria.
Most often dogs with detrusor hyperreflexia have an underlying cystitis caused by bacteria, cystic calculi, neoplasia, polyps
or drugs (cyclophosphamide). Occasionally, idiopathic detrusor hyperreflexia can occur and medical management can be beneficial
in controlling signs. A cystometrogram is the gold standard for evaluating urinary bladder function in these dogs when previous
diagnostics have not delineated a cause. Spontaneous contractions of the detrusor do occur in some normal dogs and sometimes
in dogs with USMI.
In dogs with low urethral tone, spontaneous detrusor muscle contractions result in further incontinence; spontaneous contractions
of the detrusor in normal dogs does not result in incontinence due to normal urethral tone. Oxybutynin and flavoxate have
resulted in continence in dogs that have failed to improve with PPA alone. Oxybutynin, tolterodine and some newer anticholinergics
as well as tricyclic antidepressants (imipramine, clomipramine) have anticholinergic properties that can be considered for
treatment of dogs with refractory idiopathic urinary incontinence.
Dr. Hoskins is owner of DocuTech Services. He is a diplomate of the American College of Veterinary Internal Medicine with
specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200, or e-mail:
What's your question?
Send your pediatric/geriatric related questions to: Pediatric/Geriatric Protocol, DVM Newsmagazine, 7500 Old Oak Blvd., Cleveland,
OH 44130. Your questions will be answered by Dr. Hoskins in upcoming columns.