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Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • Inability to control urination with the involuntary passage of urine
  • Incontinence develops when intravesical pressure exceeds resting urethral sphincter pressure

Pathophysiology!!navigator!!

  • 3 types of bladder paralysis: (1) reflex or UMN bladder (also known as spastic or autonomic bladder); (2) paralytic or LMN bladder; and (3) myogenic or non-neurogenic bladder
    • Initially, a UMN bladder is characterized by increased urethral resistance, leading to increased intravesical pressure before voiding can occur. Voiding may occur as short bursts of urine passage with incomplete bladder emptying, and rectal examination will reveal a turgid bladder, small to increased in size
    • In contrast, LMN and myogenic bladder paresis result in chronic bladder distention due to decreased or absent detrusor activity. Rectal palpation reveals a large, flaccid bladder and urine can usually be expressed by placing pressure on the bladder
    • Although signs of a UMN bladder are initially different from those of the other 2 types, this type of problem is usually not recognized in horses until more significant incontinence develops in association with progressive loss of detrusor function
    • LMN disease limited to the external urethral sphincter with normal detrusor function has not been well documented in horses but may be related to hypoestrogenism in an occasional mare
    • By the time incontinence develops into a clinically important problem, the inciting cause can often not be determined
  • In young horses, ectopic ureter; affected horses also posture and urinate normally when ectopic ureter is a unilateral problem

Systems Affected!!navigator!!

  • Renal/urologic
  • Nervous
  • Musculoskeletal

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

Low

Signalment!!navigator!!

Breed Predilections

None documented.

Mean Age and Range

Ectopic ureter is an anomaly of development and results in incontinence from birth.

Predominant Sex

  • Bladder paralysis appears to be more common in male horses owing to the longer urethra
  • Postpartum mares may also be at greater risk for incontinence because of trauma sustained during parturition
  • An occasional mare may also develop incontinence consequent to hypoestrogenism

Signs!!navigator!!

  • Urinary incontinence and scalding of the perineal area (mares) and inner aspect of the hindlimbs in both sexes
  • Horses may appear painful while posturing to urinate or may not assume a normal voiding posture. Horses may also pass urine involuntary and appear unaware of voiding
  • Incontinence may be more apparent during exercise
  • Weakness, ataxia, etc., if incontinence is due to an underlying neurologic disease
  • Fever, partial anorexia, weight loss may be observed if complicated by pyelonephritis

Causes!!navigator!!

  • Neurologic disease—equine herpes myelopathy, EPM, spinal cord compression, cauda equina neuritis
  • Intoxication—grazing Sorghum hybrids (sudangrass and Johnson grass) that contain hydrocyanic acid
  • Trauma—postbreeding or postpartum in mares; direct injury to the urethral sphincter may occur and lead to urinary incontinence (and infertility)
  • Hypoestrogenism—a suspected cause of incontinence in an occasional mare
  • Ectopic ureter—young horses
  • Idiopathic—possibly a consequence of lumbar pain/orthopedic disease resulting in posturing difficulty and incomplete bladder emptying, perhaps more common in male horses, which would lead to accumulation of crystalline sludge in the ventral aspect of the bladder (sabulous urolithiasis), progressive bladder distention, loss of detrusor function, and paralysis (myogenic bladder)

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Normal estrous behavior in mares.

CBC/Biochemistry/Urinalysis!!navigator!!

  • CBC normal unless UTI extends to upper urinary tract, leading to variable leukocytosis
  • Blood urea nitrogen and creatinine normal unless complicated by moderate to severe bilateral pyelonephritis
  • Urine specific gravity usually normal (1.020–1.035) but increased numbers of red blood cells, white blood cells, and bacteria on urine sediment examination if complicated by UTI

Other Laboratory Tests!!navigator!!

Quantitative urine culture should be performed in all cases of incontinence.

Imaging!!navigator!!

  • Transabdominal ultrasonography—renal parenchymal architecture may be abnormal if complicated by pyelonephritis (see chapter Urinary tract infection (UTI))
  • Transrectal ultrasonography—allows assessment of bladder size and wall thickness and may demonstrate accumulation of sabulous material
  • Abdominal radiography—IV pyelography may confirm ectopic ureter in foals with incontinence; intrarenal pyelography (contrast injected transabdominally directly into renal pelvis) has a greater likelihood of outlining the ectopia
  • Urethroscopy/cystoscopy—useful to assess bladder mucosa for inflammation, accumulation of sabulous material, and integrity of ureteral orifices (they may be wide open with chronic bladder paralysis supporting vesiculoureteral reflux and probable ascending pyelonephritis)
  • Lumbar radiographs ± nuclear scintigraphy—to evaluate possible thoracolumbar musculoskeletal disease

Other Diagnostic Procedures!!navigator!!

  • Bulbocavernosus reflex (male horses)—when normal, contraction of the urethral sphincter can be palpated per rectum when the glans penis is gently squeezed by an assistant
  • Cystometry—continuous recording of intravesical pressure during saline infusion to assess detrusor muscle function; threshold for onset of detrusor contraction in normal horses is 90 ± 20 cmH2O
  • Urethral pressure profile—after passage of a balloon-tipped catheter into the bladder, the pressure in the balloon is continuously recorded as the catheter is withdrawn through the urethral sphincter to assess external sphincter muscle function; the pressure in normal horses typically exceeds 100 cmH2O and waves of contractions can be appreciated on the tracing
  • Neurologic examination—document additional neurologic deficits
  • Collection and analysis of cerebrospinal fluid—cytologic analysis and appropriate testing for EPM
  • Electromyography—assess perineal and tail muscles for evidence of denervation (LMN disease)

Pathologic Findings!!navigator!!

  • The bladder often contains a concretion of chalky/sabulous material
  • The bladder mucosa may be thickened and hemorrhagic with a neutrophilic or lymphocytic infiltrate
  • Attempts to investigate the neurologic component of the urinary incontinence are often challenging (no lesions may be identifiable)

Treatment ⬆ ⬇

Outline

TREATMENT

Nursing Care!!navigator!!

  • Daily cleaning of perineum and hindlimbs to minimize skin irritation from incontinence; application of petrolatum to scalded areas
  • In cases of myogenic bladder and sabulous urolithiasis, manual lavage of the bladder with saline may provide temporary relief of distention and can remove accumulated urine sediment
  • Proper recognition and treatment of all underlying primary neurologic disease processes

Activity!!navigator!!

  • In cases of neurologic disease, advise not to ride the horse until resolution of ataxia or other underlying conditions
  • If gait is normal and the horse is outwardly healthy, mild to moderate exercise may be continued

Diet!!navigator!!

  • Removal from exposure to cyanogenic grasses
  • Grass hay is preferable to alfalfa or other legumes (higher in calcium)
  • Urine acidifying agents can be supplemented (NH4Cl or (NH4SO4) or an anionic diet can be fed in an attempt to limit urine crystal formation; however, no currently available products are palatable enough to be efficacious
  • NaCl 28–56 g (1–2 ounces) BID added to feed or mixed with water and administered as an oral slurry will increase urine flow and decrease sedimentation of crystalloid material in the ventral aspect of the bladder

Client Education!!navigator!!

Urinary incontinence can be managed but requires dedication and repeated examinations and treatments for UTI.

Surgical Considerations!!navigator!!

Surgical correction of ectopic ureter by unilateral nephrectomy or attachment of the distal ureter to the bladder neck.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Bethanechol 0.25–0.75 mg/kg SC or PO every 8 h—parasympathomimetic agent selective on smooth muscle of the GI tract and bladder; response to treatment is usually poor because of longstanding detrusor paresis/paralysis before the problem is clinically recognized (except perhaps with acute herpes myelopathy or EPM). If no improvement is noted within 3–5 days of treatment, therapy should be discontinued
  • Phenoxybenzamine 0.7 mg/kg PO every 6 h—α-adrenergic blocker that can be used to decrease urethral sphincter tone in cases of UMN bladder
  • Estradiol cypionate 4 µg/kg IM every other day—may improve urethral sphincter tone in mares with hypoestrogenism-associated incontinence
  • Antimicrobials—trimethoprim–sulfonamide combination (sulfadiazine preferable to sulfamethoxazole because of less hepatic metabolism) 20 mg/kg PO every 12 h or 24 h; is the most practical long-term treatment; can be used prophylactically or therapeutically for established UTI (see chapter Urinary tract infection (UTI))

Contraindications!!navigator!!

N/A

Precautions!!navigator!!

Bethanechol—must be used cautiously as it may increase GI motility and lead to colic signs.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Patient monitoring in cases of neurogenic bladder should include regular repeat physical and neurologic examination, cystometry, and urethral pressure profiles could be repeated at 2–4 week intervals if clinical improvement is uncertain
  • Monitoring of patients with longstanding idiopathic incontinence should include regular (weekly or monthly) assessment of overall condition (attitude, appetite, body weight, etc.)

Possible Complications!!navigator!!

  • Moderate to severe dermatitis consequent to urine scald
  • Sabulous urolithiasis
  • UTI—cystitis, possibly complicated by ascending pyelonephritis

Expected Course and Prognosis!!navigator!!

  • The prognosis for recovery of cases of bladder paresis/paralysis and associated incontinence due to neurologic disease is guarded and will depend on response to treatment of the underlying disease and duration of paresis/incontinence (generally more favorable if <2 weeks in duration); evidence of some detrusor function on cystometry and a normal urethral pressure profile improve the prognosis and such horses warrant aggressive treatment
  • The prognosis for recovery of cases of longstanding “idiopathic” bladder paralysis and associated incontinence is poor; owner frustration often leads to a decision for euthanasia within a few months after the problem is first recognized

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Infertility (mares).

Age-Related Factors!!navigator!!

Hypoestrogenism would be more likely in older mares, and ectopic ureter is a problem recognized in young horses.

Zoonotic Potential!!navigator!!

None

Pregnancy/Fertility/Breeding!!navigator!!

N/A

Synonyms!!navigator!!

Enzootic ataxia and cystitis (herd outbreaks associated with intoxication).

Abbreviations!!navigator!!

  • EPM = equine protozoal myeloencephalitis
  • GI = gastrointestinal
  • LMN = lower motor neuron
  • UMN = upper motor neuron
  • UTI = urinary tract infection

Suggested Reading ⬆ ⬇

Bayly WM. Urinary Incontinence and Bladder Dysfunction. In: Reed SM, Bayly WM, Sellon DC, eds. Equine Internal Medicine, 4e. St. Louis, MO: WB Saunders, 2017:973–976.

Author(s) ⬆ ⬇

Author: Harold C. Schott II

Consulting Editor: Valérie Picandet

Additional Further Reading ⬆

Click here for Additional Further Reading