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Basics ⬇

Basics

Definition

Incomplete voiding unassociated with urinary obstruction

Pathophysiology

Micturition voiding phase disorder. Incomplete voiding due to neurogenic or myogenic failure, or both; associated with hypocontractility of the urinary bladder, or excessive outlet resistance, or both.

Systems Affected

  • Renal/Urologic
  • Endocrine/Metabolic
  • Neuromuscular

Geographic Distribution

  • Worldwide.
  • Dysautonomia: Europe (Great Britain, Scandinavia), USA (Midwest), sporadic cases in Dubai, New Zealand, and Venezuela.

Signalment

Species

Dog and cat

Breed Predilections

  • Chondrodystrophic breeds with IVDD.
  • Manx cats with congenital sacral spinal lesions.
  • Large-breed dogs (German shepherd dogs) with acquired cauda equina syndrome.
  • Labrador retrievers, German shorthaired pointers, German shepherd dogs with dysautonomia.

Mean Age and Range

Young adult dogs with functional urinary obstruction

Predominant Sex

More common in males than females

Signs

General Comments

Signs include primary and secondary abnormalities of voiding dysfunction.

Historical Findings

  • Frequent attempts to urinate, straining to urinate, or not voiding.
  • Attenuated, interrupted, or prolonged urine stream.
  • Urinary leakage occurs when pressure in bladder exceeds urethral outlet closure pressure (overflow or paradoxical incontinence).
  • Vomiting, lethargy, painful abdomen with rupture or inflammation of the urinary tract.

Physical Examination Findings

  • Palpably distended urinary bladder and/or inappropriate residual urine (normal 0.2–0.4 mL/kg) after attempts of voiding.
  • Possibly, abnormal neurologic examination (see “Differential Diagnosis”).
  • Rarely, abdominal distension, abdominal pain, or signs of post-renal azotemia.
  • Overflow urinary incontinence.

Causes

Hypocontractility of the Urinary Bladder (Detrusor Muscle), (Detrusor Atony)

  • Usually caused by bladder overdistension.
  • Can have neurologic dysfunction or previous urinary obstruction.
  • Neurogenic causes include lesions of the pelvic nerves, sacral spinal cord, and suprasacral spinal cord.
  • Sacral spinal cord lesions (e.g., congenital malformations, cauda equina compression, lumbosacral disc disease, and vertebral fractures/dislocations) can result in a flaccid, overdistended bladder with weak outlet resistance (lower motor neuron bladder).
  • Suprasacral spinal cord lesions (e.g., intervertebral disc protrusion, spinal fractures, and compressive neoplasms) can result in a distended, firm bladder that is difficult to express (upper motor neuron bladder).
  • Dysautonomia could lead to detrusor atony with urine retention.
  • Electrolyte disturbances or metabolic disorders associated with generalized muscle weakness can affect detrusor muscle contractility.
  • Canine hyperadrenocorticism can cause polyuria, bladder distention, and mild urine retention.
  • Drugs causing varying degrees of myogenic failure include tricyclic antidepressants, calcium channel blockers, anticholinergic agents, and opioids.

Functional Urinary Obstruction

  • Excessive or inappropriate outlet resistance prevents complete voiding during bladder contraction.
  • In patients with suprasacral spinal lesions (typically T3–L3) or midbrain disorders, urethral outlet resistance becomes uninhibited and remains excessive or is not coordinated with voiding contractions (detrusor-urethral dyssynergia).
  • Associated with sacral lesions and local neuropathy.
  • Idiopathic.
  • Excessive urethral resistance (often called urethrospasm) may be seen after urethral obstruction or in association with urethral or pelvic surgery, urethral inflammation, or prostate disease.

Risk Factors

  • Urethral obstruction
  • Pelvic or urethral surgery
  • Anticholinergic medications
  • Epidural analgesia

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • When no voiding is observed, differentiate from oliguria, anuria, and urinary tract rupture.
  • Differentiate from physical and mechanical obstruction. Clinical signs associated with urinary obstruction include pollakiuria, stranguria, and hematuria; patients with mechanical obstruction may void a few drops of urine after long periods of straining.
  • Neurologic findings in dogs with supraspinal lesions affecting micturition include paralysis or paresis of pelvic and sometimes thoracic limbs, hyperreflexia of affected limbs, and cervical, thoracolumbar, and lumbar pain. The bladder is usually distended, firm, and difficult to express. In patients with chronic or partial lesions, reflexive voiding may return, characterized by incomplete, involuntary detrusor contractions with outlet spasticity.
  • Neurologic findings in dogs with sacral lesions affecting micturition include pelvic limb paresis with hyporeflexia, depressed anal and tail tone, perineal sensory loss, and depressed bulbospongiosus reflexes. Lumbosacral pain can be the only sign. The bladder is typically distended, flaccid, and easy to express.
  • A urine stream that can be initiated but is abruptly halted is typical of idiopathic detrusor-urethral dyssynergia. Manual palpation may confirm detrusor contractions, which persist after flow terminates, and may suggest a high residual urine volume.
  • In patients recovering from urinary obstruction, inability to void may result from re-obstruction, excessive (functional) urethral resistance, or detrusor atony caused by overdistension. If the urinary bladder can be expressed via gentle palpation applied through the abdomen, detrusor atony is likely. If resistance to manual expression is encountered and urethral obstruction can be ruled-out by examination or transurethral catheterization, functional obstruction is likely.
  • Clinical signs accompanying urine retention in patients with dysautonomia may include mydriasis, prolapsed third eyelids, xerostomia, regurgitation or vomiting, megaesophagus, reduced or absent anal tone, diarrhea or constipation, and bradycardia.

CBC/Biochemistry/Urinalysis

  • Test results rule-out metabolic causes of neuromuscular disease; also used to evaluate post-renal azotemia.
  • Urinalysis may reveal UTI, trauma, or inflammation.

Imaging

  • Use survey radiographs and ultrasound to rule-out obstructing uroliths, pelvic trauma, lumbosacral disease, caudal abdominal masses.
  • Use contrast cystourethrography or vaginourethrography, or occasionally, cystourethoscopy, to rule-out obstructive lesions.
  • Use myelography, epidurography, CT, MRI to localize neurologic lesions.

Diagnostic Procedures

  • Neurologic exam-assessment of caudal spinal and peripheral nerve function through examination of anal tone, tail tone, perineal sensation, and bulbospongiosus reflexes.
  • Transurethral catheterization may be required to rule-out urethral obstruction; catheters should pass easily in animals with no mechanical obstruction and in those with extramural urethral compression (e.g., caused by a smooth bladder neck mass, a large prostate gland, or a caudal abdominal mass).
  • Diagnosis of dysautonomia is based on systematic pharmacologic testing of autonomic responses.
  • Use urodynamic procedures to confirm detrusor atony or functional urethral obstruction, or to document detrusor-urethral dyssynergia; detrusor areflexia may be documented by cystometrographic studies; inappropriate urethral resistance or urethral spasm occasionally is documented by resting urethral pressure profilometry; combined cystometry and urethral pressure measurements or uroflow studies are necessary to document dyssynergia.

Pathologic Findings

Detrusor Atony

  • Previously overdistended bladder may not be discernable on gross pathology.
  • Caudal vertebral hypoplasia or aplasia and various sacral spinal cord lesions (abnormal cover, meningomyeloceles, intradural lipomas) in some Manx cats.
  • Light microscopy in chronic cases may show widespread degeneration of smooth muscle cells, cholinergic axons, and intrinsic nerves.

Functional Urethral Obstruction

  • Various suprasacral neurologic diseases (e.g., IVDD, FCE)
  • Urethritis
  • Prostatitis

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

Usually managed as inpatients until adequate voiding function returns.

Nursing Care

  • Manage azotemia, electrolyte imbalances, and acid-base disturbances associated with acute urine retention (rare).
  • Identify UTI and treat appropriately.
  • Keep the urinary bladder small by intermittent or indwelling transurethral catheterization or frequent manual compression.

Client Education

Advise clients that complete voiding function may not return. Monitor for signs of complete obstruction, uremia, and UTI.

Surgical Considerations

Consider surgical options for salvaging urethral patency in some patients; perineal urethrostomy indicated in male cats with unmanageable distal urethral resistance.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

Detrusor Atony

  • Bethanechol (5–25 mg/dog PO q8–12h; 1.25–7.5 mg/cat q8–12h)-a cholinergic agent; may increase detrusor contractile input in partially denervated or acutely overdistended bladders.
  • Metoclopramide (dog and cat, 0.2–0.5 mg/kg PO q8h)-a dopamine antagonist; may stimulate detrusor contraction.
  • Cisapride (dog, 0.5 mg/kg PO q8h; 1.25–5 mg/cat q8–12h)-a smooth muscle prokinetic agent; may promote bladder emptying.

Functional Urethral Obstruction

  • Prazosin (dog, 1 mg/15 kg PO q8–24h; cat, 0.25–0.5 mg/cat PO q12–24h or 0.03 mg/kg IV) or phenoxybenzamine (dog, 0.25–0.5 mg/kg PO q12–24h; cat, 1.25–7.5 mg/cat PO q12–24h)--adrenergic antagonists reduce smooth muscle contraction in the urethra
  • Diazepam (dog, 2–10 mg/dog PO q8h; cat, 1–2.5 mg/cat PO q8h or 0.5 mg/kg IV)-relaxes striated muscle of the external urethral sphincter.
  • Acepromazine (dog, 0.5–2 mg/kg PO q6–8h; cat, 1–2 mg/kg PO q6–8h)-a phenothiazine tranquilizer and general muscle relaxant with -adrenergic blocking effects on urethral tone; may be effective in cats with excessive urethral resistance.
  • Dantrolene (dog, 1–5 mg/kg PO q8–12h; cat, 0.5–2 mg/kg PO q8h or 1 mg/kg IV) striated muscle relaxant; appears to be effective in reducing distal urethral resistance in cats.
  • Baclofen (dog, 1–2 mg/kg PO q8h)-a spinal reflex inhibitor; acts as a skeletal muscle relaxant; limited clinical evaluation in dogs and cats.

Contraindications

  • Baclofen in cats.
  • Acepromazine, phenoxybenzamine, and prazosin have vasodilatory effects-use with caution in volume-depleted or azotemic patients and those with cardiac disease.
  • Acepromazine and diazepam-can cause sedation; use with caution in lethargic patients.

Precautions

  • Confirm adequate outlet for urine flow before administering bethanechol since it can increase muscular contraction of the urinary bladder neck and proximal urethra. Pretreat with -agonists (e.g., phenoxybenzamine, prazosin).
  • Prazosin may cause potent “first-dose” hypotension; to minimize risk, initial dosage should be one-half of total dosage.
  • Acute hepatopathyas uncommon complication of oral diazepam in cats.

Possible Interactions

Cisapride can enhance the sedative effect of diazepam.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Reassess residual urine volume by urinary bladder palpation or by periodic transurethral catheterization.
  • Slowly withdraw medications after primary causes are corrected and adequate voiding function has occurred for several days.
  • Perform serial urinalysis and urine culture to detect UTI in patients with chronic urine retention.

Possible Complications

  • UTI
  • Permanent detrusor muscle injury and atony; bladder or urethral rupture
  • Post-renal azotemia

Expected Course and Prognosis

  • Good for acute detrusor atony caused by overdistension, acute reversible neurologic lesions, acute functional obstruction associated with irritative urethral disorders or resolving obstruction-recovery often occurs within 1 week.
  • Fair to poor for chronic detrusor atony or chronic functional obstruction-urinary function usually recovers as motor function of the limbs recovers. If functional obstruction responds to -agonists, prolonged administration may be required.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

  • UTI
  • Azotemia

Pregnancy/Fertility/Breeding

Bethanechol is contraindicated

Synonyms

  • Dysfunctional voiding
  • Neuropathic bladder
  • Reflex dyssynergia, detrusor-urethral dyssynergia
  • Urethrospasm

Abbreviations

  • CNS = central nervous system
  • UTI = urinary tract infection

Suggested Reading

Labato MA., Acierno MJ.Micturition disorders and urinary incontinence. In: Ettinger SJ, Feldman EC, eds., Textbook of Veterinary Internal Medicine, 7th ed. St. Louis: Saunders Elsevier, 2010, pp. 160–164.

Author Steffen O. Sum

Consulting Editor Carl A. Osborne

Acknowledgment The author and editors acknowledge the contribution of Kip Carter for the illustrations in the electronic version, and Jeanne A. Barsanti for review.

Client Education Handout Available Online