Micturition disorders result from abnormal storage or voiding of urine. Clinical signs can include unconscious passage of urine (urinary incontinence), dribbling of urine, or difficulty with urination, including an abnormal urine stream. Diagnosis depends on a careful evaluation of history, a comprehensive physical examination (including observation of urination), and diagnostic testing including urinalysis and potential imaging or advanced procedures to visualize the urinary tract. Treatment depends on the underlying cause.
Disorders of micturition result from dysfunctional storage or voiding of urine.
Urinary incontinence is the failure of voluntary control of micturition, with constant or intermittent unconscious passage of urine. Incontinent animals may leave a pool of urine where they have been lying or may dribble urine while walking. The coat around the vulva or prepuce can be wet, and perivulvar or peripreputial dermatitis can result from urine scalding.
Failure of urine storage is characterized by inappropriate leakage of urine or urinary incontinence due to lack of adequate urethral tone, failure of bladder relaxation, and anatomical defects.
Animals with urine storage disorders have a normal residual urine volume in the bladder after voiding. Urethral sphincter mechanism incompetence (USMI) is the most common cause of urinary incontinence secondary to failure of urine storage in dogs. USMI is usually attributed to a deficiency of sex hormones in neutered animals, particularly female dogs, and is referred to as hormone-responsive urethral incompetence. Idiopathic USMI also occurs.
Ectopic ureters are a congenital anatomical defect resulting in one or both ureteral openings terminating somewhere distal to the bladder trigone. Detrusor instability or overactive bladder often accompanies cystitis but can also be idiopathic.
Failure of normal voiding is characterized by frequent attempts to urinate with stranguria and passage of only small amounts of urine.
Animals with voiding disorders have an increased residual urine volume after voiding or attempts to void. Inability to urinate can be due to mechanical urethral obstruction by calculi, neoplasia, strictures, or other intraluminal or extraluminal obstructions; detrusor atony from prolonged overdistention of the bladder; and idiopathic functional urethral obstruction (reflex dyssynergia in dogs/detrusor urethral dyssynergia).
Neurological causes of micturition disorders are often categorized as upper motor neuron (UMN) or lower motor neuron (LMN) lesions. Lesions in the sacral spinal cord or pelvic nerve, as well as detrusor atony, lead to LMN signs, which are characterized by a distended, easily expressed bladder. Anal tone and perineal reflex are decreased. Although LMN bladders are easily expressed, affected animals may be unable to void voluntarily.
Spinal cord lesions cranial to the sacral segments lead to an interruption in inhibition of pudendal and hypogastric nerves, resulting in failure of the urethral sphincter to relax, as well as difficult manual expression. Affected animals typically also have hindlimb paresis or plegia in association with their spinal cord lesion.
Animals with neurogenic incontinence may leak urine (with LMN lesions) and/or develop overflow incontinence because of urine dribbling associated with bladder overdistention (any neurogenic cause).
Diagnosis of Micturition Disorders in Dogs and Cats
Patient history and clinical examination with observation of urine voiding
Laboratory evaluation, including urinalysis
Advanced diagnostics (eg, abdominal imaging, urodynamic testing, and cystoscopy)
A thorough history and physical examination (including neurological examination) and observation of urine voiding (including estimation of initial and final bladder volumes) are the most important components of a workup for micturition disorders. Disorders of micturition must also be differentiated from other disorders that result in inappropriate urination, such as polyuria/polydipsia, urinary tract infections, and behavioral problems.
USMI most often affects spayed female dogs and may be more apparent in middle-aged to older dogs, when comorbid conditions can make incontinence more apparent or problematic. Typically, animals unconsciously leak urine when sleeping or recumbent but are able to void normally otherwise. Diagnosis is often presumptive, based on signalment, history, and physical examination, as well as response to empirical therapy.
Ectopic ureters occur in juvenile dogs—more often females—and lead to lifelong constant urine dribbling because the ureter(s) open in a location distal to the urethral sphincter. Cystoscopy is the most sensitive and specific way to diagnose ectopic ureters; however, it is often preceded by CT and/or ultrasonography of the urinary tract to evaluate the remainder of the tract for concurrent abnormalities.
Detrusor instability/overactive bladder can resemble increased urination frequency, dribbling after normal voiding, or involuntary urination with activity. Definitive diagnosis requires urodynamic evaluation; however, a therapeutic trial may also be chosen.
Idiopathic functional urethral obstruction (reflex dyssynergia/detrusor urethral dyssynergia) is an uncommon disorder that occurs primarily in middle-aged male dogs of large or giant breeds. Clinical signs can be difficult or impossible to distinguish from those of a mechanical urethral obstruction; they include repeated posturing to urinate and a urine stream that may start out normal but rapidly decreases to a dribble or stops entirely. Postvoiding residual urine volume is greater than normal. Urinary incontinence can result from persistent overfilling of the bladder (overflow incontinence) and can be mistaken for a storage disorder.
In contrast to mechanical obstructions, idiopathic functional urethral obstruction allows a urinary catheter to pass easily to facilitate emptying of the bladder. Mechanical obstructions must be ruled out (via contrast urethrography, CT, and/or urethrocystoscopy), after which this diagnosis is often presumptive.
Detrusor atony occurs when impaired voiding results from a failure of the detrusor muscle to contract and allow the bladder to empty. Detrusor atony can occur secondary to neurological lesions (as in LMN bladder) or can be due to detrusor muscle damage resulting from severe, prolonged overdistention of the bladder due to mechanical or functional obstruction.
Treatment of Micturition Disorders in Dogs and Cats
Pharmacological intervention
Surgery
Supportive care
Dogs with USMI can be treated with the alpha-adrenergic receptor agonist phenylpropanolamine (2 mg/kg, PO, every 8–12 hours) or, in female dogs, estrogen compounds such as estriol (2 mg/dog, PO, every 24 hours for 14 days, then decreased to 1 mg/dog every 24 hours) or diethylstilbestrol (0.1–1 mg/dog, PO, every 24 hours for 5 days, then decreased to once weekly or lowest effective dose and frequency). Phenylpropanolamine and estriol are approved for use in dogs, but diethylstilbestrol is available only through compounding.
Phenylpropanolamine and an estrogen compound can be used in combination if single-agent therapy is ineffective. For dogs that do not respond to pharmacological intervention, urethral bulking agents (cross-linked collagen) can be injected into the proximal urethra with cystoscopic guidance. Alternatively, surgical placement of an artificial urethral sphincter can restore continence in cases refractory to medical management.
Ectopic ureters cannot be treated effectively with medical management and require interventional or surgical procedures. The treatment of choice is cystoscopic ablation of intramural ectopic ureters. Extramural ectopic ureters (a minority of cases) must be surgically reimplanted. Detrusor instability is treated with anticholinergic drugs such as oxybutynin chloride (0.2–0.3 mg/kg, PO, every 8–12 hours indefinitely, to maintain urinary continence).
Idiopathic functional urethral obstruction (reflex dyssynergia/detrusor urethral dyssynergia) is treated with the alpha-adrenergic antagoniststamsulosin (0.4–0.8 mg/dog, PO, every 24 hours or, in some cases, every 8–12 hours) or prazosin (0.5–3 mg/dog, PO, every 8–12 hours) indefinitely or until the condition resolves. In severe cases, intermittent urethral catheterization might be needed. Although phenoxybenzamine was used historically, it has largely been replaced by prazosin and tamsulosin because of their alpha-1 selectivity and more consistent efficacy.
Detrusor atony resulting from prolonged overdistention of the bladder might respond tobethanechol (2.5–25 mg/dog, PO, every 8–24 hours; 1.25–5 mg/cat, PO, every 8 hours until urinary bladder contractility is restored) to promote bladder contraction. Bethanechol should be administered after the urethral obstruction that led to bladder overdistention has been relieved. The bladder should be kept empty for the first week to allow repair of the detrusor muscle with indwelling urinary catheterization or frequent intermittent catheterization.
Complete mechanical obstruction of the urethra is a medical emergency and should be relieved by catheterization and retropulsion of the obstructing material into the bladder, or by surgery.
Also see Pharmacotherapeutics in Urine Retention in Animals.
Key Points
A thorough history and attentive physical examination, including observation of voiding and estimation of pre- and postvoiding bladder volumes, are essential to accurately identify and classify micturition disorders.
The most common micturition disorder resulting in urinary incontinence is urethral sphincter mechanism incompetence, most often in spayed female dogs.
Many disorders of micturition can be effectively managed with appropriate pharmacological intervention; interventional or surgical procedures are required in some cases.
For More Information
Kendall A, Byron JK, Westropp JL, et al. ACVIM consensus statement on diagnosis and management of urinary incontinence in dogs. J Vet Intern Med. 2024;38(2):878-903.
Byron JK. Micturition disorders. Vet Clin North Am Small Anim Pract. 2015;45(4):769-782.
Also see pet owner content regarding noninfectious diseases of the urinary system in dogs and cats.
