The diagnosis of USMI can be made based on signalment, history and lack of any other cause of urinary incontinence found on
diagnostics. Because many of these dogs are older, it is crucial to evaluate these dogs for polyuria. If another disorder
causing polyuria is documented (e.g., hyperadrenocorticism), one should treat the disorder first before suggesting more invasive
treatments for the urinary incontinence. A urethral pressure profile is the gold standard and further urodynamics should be
considered in refractory dogs. Other neurologic abnormalities pertaining to the urinary bladder such as detrusor instability
may occur simultaneously and contribute to urinary incontinence.
Medical management of USMI includes the use of drugs aimed at improving urethral tone via the alpha-1 adrenoceptors. Phenylpropanolamine
(PPA) is currently the drug that results in continence in the most dogs, but this drug needs to be given at least two to three
times daily. Clinically, some have had more successful outcomes using the extended release formulation but there are no published
results comparing extended release versus standard formulation. The dose can be titrated from 1-2 mg/kg SID-TID. Side effects
in dogs include restlessness, anxiety, hypertension and tachycardia. Phenylpropanolamine is not recommended in dogs with cardiac
disease or hypertension.
Estrogens may also be used for USMI and these hormones are thought to sensitize the alpha-1 adrenoceptors and indirectly result
in an improvement in the closure pressure. Due to the possibility of bone-marrow suppression, the lowest possible dose of
estrogen should be used. Diethylstilbestrol (DES) is still commonly used; however, premarin (conjugated estrogen) has been
administered with successful resolution of urinary incontinence in many dogs. Bone-marrow suppression has been described in
dogs receiving older generation depot estrogens and in those receiving much higher doses of DES. If the dog is still experiencing
urinary incontinence while receiving phenylpropanolamine, estrogen can be given concurrently. DES can be prescribed at 0.5-1.0
mg per dog once daily for five to seven days and then decrease the dose to the lowest effective dose, often once or twice
Submucosal urethral collagen injections are now available for animals that are refractory to medications or for owners who
do not wish to continually medicate their pets. Dogs are placed under general anesthesia and three to four collagen deposits
(Contingen(r), Bard collagen implant) are injected in a circular fashion approximately 1.5 cm distal to the trigone via the
cystoscope. Some dogs still require medications after this procedure, but greater continence is usually gained following the
implants when drugs were previously ineffective. A second series of implants may be needed to improve continence in some dogs.
Twenty-seven of 40 (68 percent) dogs in a recent study were continent for a mean 17 months (one-64 months range). In 10 of
40 dogs, continence was improved following collagen treatments, and in six of these 10 dogs full continence was gained with
medication. Some dogs with initial full continence deteriorated after one year. Retreatment with collagen is usually easier
and often successful in gaining continence in these dogs. In another recent study, mean continence scores following collagen
implant treatment increased considerably over scores while on medication.
Novel treatment of USMI in ovariectomized dogs has been reported with use of GnRH (gonadotropin releasing hormone) analogs.
Luteinizing hormone (LH) and follicle stimulating hormone (FSH) increase dramatically in spayed dogs probably due to a lack
of feedback function on the hypothalamic-pituitary system. Activation of FSH and LH receptors in the urethra and urinary bladder
may have some effects that increase incontinence in some dogs by mechanisms that are not yet clear. It is theorized that urinary
incontinence might be controlled by suppressing FSH and LH. This can be accomplished by administration of GnRH-analogues that
will down-regulate the GnRH-receptors in the pituitary gland. In one study, complete continence was gained in seven of 11
dogs following treatment with GnRH analogs for a mean of 247 days (50 to 738 days). The addition of PPA treatment to the remaining
four dogs resulted in complete continence for three. All dogs had previously failed conventional medical therapy for USMI.
FSH and LH concentrations were increased in these bitches before treatment and were decreased following treatment often to
undetectable levels. Estrogen treatments that are effective in regaining continence in about two-thirds of dogs with USMI
may exert their effects in a similar way by decreasing FSH and LH.