Canine Urinary Incontinence Study Guide

Overview and Clinical Importance

Urinary incontinence (UI) is defined as the passive, involuntary leakage of urine. This is a common clinical problem in dogs, affecting 3-20% of spayed female dogs and a smaller percentage of male dogs. Understanding the pathophysiology, diagnostic approach, and treatment options is essential for NAVLE success and clinical practice.

UI significantly impacts the quality of life for both pets and owners. Many cases are treatable with appropriate medical or surgical intervention, making accurate diagnosis crucial. The 2024 ACVIM Consensus Statement provides the current standard of care for diagnosis and management.

Physiology of Micturition

Normal micturition involves two phases: storage and voiding. Understanding the neural control is essential for diagnosing and treating incontinence.

Neural Control of the Lower Urinary Tract

Board Tip - Memory Aid for Innervation: "S = Storage, P = Peeing" - Sympathetic nervous system controls Storage (relaxes bladder, contracts sphincter), Parasympathetic controls Peeing (contracts detrusor for voiding). The Pudendal nerve provides voluntary external sphincter control.

Classification of Urinary Incontinence

UI is classified into two main categories based on the underlying dysfunction:

Urethral Sphincter Mechanism Incompetence (USMI)

USMI (also called hormone-responsive incontinence or spay incontinence) is the most common cause of acquired UI in adult dogs. It accounts for approximately 80% of UI cases in spayed female dogs.

Pathophysiology

USMI results from inadequate urethral closure pressure to maintain continence. Contributing factors include:

• Decreased estrogen leading to reduced alpha-adrenergic receptor sensitivity
• Changes in collagen content and smooth muscle tone
• Pelvic bladder position reducing transmitted abdominal pressure
• Shorter urethral functional length

Signalment and Risk Factors

Clinical Signs

The hallmark clinical presentation includes:

• Involuntary urine leakage primarily when lying down, relaxed, or sleeping
• Wet bedding or puddles where the dog has been resting
• Normal voluntary urination (the dog can urinate normally when awake)
• Dog is typically unaware of the urine leakage
• Perivulvar dermatitis and urine scalding may develop secondarily

Ectopic Ureters

Ectopic ureters (EU) are the most common congenital cause of UI in young dogs. An ectopic ureter opens distal to the normal position at the bladder trigone, bypassing the urethral sphincter mechanism.

Classification

Signalment

• Primarily juvenile dogs (less than 1 year of age)
• Females affected 4-20 times more commonly than males
• Predisposed breeds: Siberian Husky, Labrador Retriever, Golden Retriever, Newfoundland, Poodle, Bulldog, West Highland White Terrier, Soft-Coated Wheaten Terrier

Board Tip - EU Memory Aid: "HUSKY puppies LEAK" - Siberian Huskies are the classic breed for ectopic ureters. Think of any young dog that has never been housetrained and constantly dribbles urine. Females are far more commonly affected.

Diagnostic Approach

History and Pattern Recognition

A thorough history is essential to differentiate storage from voiding disorders:

Physical Examination

Critical components of the physical examination include:

• Bladder palpation: Assess size, distension, pain, and position before and after voiding
• Rectal examination: Palpate urethra along pelvic floor and prostate in males
• Vulvar examination: Check for perivulvar dermatitis, hooding, or anatomical abnormalities
• Neurological assessment: Evaluate perineal reflex, anal tone, tail tone, and proprioception

Postvoiding Residual Volume (PVRV)

PVRV is a critical diagnostic tool measured within 10 minutes of voiding:

• Normal: 0.2-1.0 mL/kg (storage disorder likely if PVRV normal)
• Abnormal: Greater than 3 mL/kg (indicates urine retention/voiding disorder)
• Equivocal: 1-3 mL/kg (interpret with clinical context)

Laboratory Testing

Urinalysis and urine culture should be performed in all dogs with UI:

• UTI can cause or exacerbate UI
• If culture positive, treat with appropriate antibiotics for 5 days per ISCAID guidelines
• Obtain negative culture before interventional procedures

Diagnostic Imaging

Treatment of Urinary Incontinence

Medical Management of USMI

Treatment Algorithm for USMI

• First-line: PPA or estrogen (estriol preferred) for females; PPA for males
• Non-responders: Switch to alternative drug or combine PPA + estrogen
• Males refractory to PPA: Consider testosterone cypionate after confirming normal PVRV
• Medical failure: Urethral bulking agents or artificial urethral sphincter (AUS)

Interventional and Surgical Treatment

Urethral Bulking Agents

Cystoscopic injection of bulking agents (crosslinked collagen) into the proximal urethra:

• Greater than 80% achieve initial continence
• Effect may diminish within 1 year; re-treatment possible
• Best for older dogs with acquired USMI

Artificial Urethral Sphincter (AUS)

Surgically implanted hydraulic cuff around the urethra:

• 82-92% achieve good to excellent continence
• Durable long-term results (2-3 years documented)
• Requires follow-up for device adjustments
• Complications: Urethral stricture (0-17% requiring removal)

Cystoscopic Laser Ablation for Ectopic Ureters

Minimally invasive treatment for intramural EU:

• Diode or holmium YAG laser used to reposition ureteral opening
• 47-72% continent without additional treatment
• 77-82% continent with added medical management for concurrent USMI
• Outpatient procedure with minimal complications

Neurogenic Urinary Incontinence

Neurological lesions affecting bladder innervation cause distinct patterns of incontinence:

Board Tip - UMN vs LMN Bladder: "UMN = Uptight bladder" (firm, hard to express, sphincter hyperreflexia). "LMN = Lax bladder" (flaccid, easily expressed, overflow incontinence). Both result in urinary retention, but LMN lesions cause decreased anal and perineal reflexes.