45. Disorders of elimination of urine (incontinence, retention)

What is urinary incontinence?

The inability to voluntarily control urination, resulting in constant or intermittent involuntary urination. It is most common in large breed, spayed female dogs

What are some aetiologies of urinary incontinence?

1. Neurologic (disruption of neuroreceptors, lesions on the sacral spinal cord, cerebellum – lower motor neuron (LMN) lesions at S1-S3 leading to decreased sphincter tone and bladder leakage)

2. Urinary bladder storage dysfunction (bladder overactivity, neoplasia, external compression)

3. Urethral disorders (hypoplasia, inflammation, prostatic disease)

4. Urethral incontinence (hormone-responsive, common in spayed bitches)

5. Anatomic abnormalities (ectopic ureter)

What are some clinical signs of urinary incontinence?

Wet coat around the vulva or prepuce, perivulvar or peripreputial dermatitis from urine scalding, pooling of urine where the animal has been lying, and dribbling urine while walking

How is urinary incontinence diagnosed?

Imaging (double contrast cystography, ultrasound), cystoscopy, and neurologic examination

How is urinary incontinence treated?

Depends on the primary cause.

1. Medications to increase bladder tone (phenylpropanolamine, propantheline) are used.

2. For hormone-responsive incontinence due to lack of oestrogen; oestrogen, oestriol or diethylstilboestrol can be used

What is urinary retention?

The inability to completely empty the bladder. It is a functional urinary retention, not associated with urinary obstruction

What is the detrusor muscle?

The muscle in the wall of the bladder; its contraction pushes urine out of the bladder

What are some aetiologies of urinary retention?

1. Hypocontractility/detrusor muscle atony (bladder overdistension, neurogenic causes – upper motor neuron (UMN) lesions, electrolyte disturbances)

2. Functional urinary obstruction (urethral spasms, sacral lesions, local neuropathy)

What are some clinical signs of urinary retention?

Palpable distended bladder, pollakiuria (ineffective or frequent urination), dysuria, and stranguria

How is urinary retention diagnosed?

Lab work, imaging, contrast cystourethrography, myelography, and neurologic examination

How is urinary retention due to detrusor atony treated?

Bethanechol (a parasympathomimetic), cisapride, and metoclopramide

How is urinary retention due to functional urethral obstruction treated?

Diazepam, acepromazine, and prazosin (to relax bladder muscles)

What biochemical change is present during urinary retention?

Azotaemia

What drugs can you give to increase activity of the detrusor muscle?

1. Bethanechol

2. Cisapride

3. Metoclopramide

Why does spaying increase risk of incontinence?

Urethral sphincter incompetence. After the dog is spayed the strength of the urethral sphincter decreases in the year following surgery, & it often continues to weaken with age.

What drug can prevent incontinence after spaying?

1. Oestrogen therapy increases the sensitivity of the closure receptors in the urethra. 

2. Phenylpropanolamine (PPA) directly stimulates closure receptors in the urethra.

What drug can be used to increase the bladder tone?

Phenylpropanolamine

What is a neurological cause for incontinence?

Damage to the sacral spinal cord (IVDD) → LMN signs

What is FLUTD and the cause?

• Feline lower urinary tract disease

• Stress

What clinical sign do owners report with urinary incontinence?

Polliakuria

What is the normal urine output per HOUR?

2-4 ml/kg/hour

What is the normal urine output per DAY?

40-50 ml/kg/day