Page 216 - Cote clinical veterinary advisor dogs and cats 4th

90 Atonic or Hypotonic Urinary Bladder

HISTORY, CHIEF COMPLAINT and intramedullary (oligodendroglioma, indicate peripheral nerve (e.g., pudendal
and sciatic nerves) disease
• Absent/weak attempts to void astrocytoma, ependymoma, metastatic ○ Nerve conduction studies (see www.
VetBooks.ir • Associated signs of neurologic dysfunction ■ ■ Infectious: discospondylitis ExpertConsult.com): decreased conduc-
[lymphoma, hemangiosarcoma])
• Leakage or dribbling of urine
tion velocity and abnormal waveform of
Traumatic: vertebral fracture/luxation,
unrelated to micturition (e.g., paresis)
PHYSICAL EXAM FINDINGS traction spinal cord injury (tail pull/ sciatic nerve indicate neuropathy (e.g.,
cauda equina, peripheral nerve)
avulsion)
• Distended bladder is characteristic. ■ Vascular: thromboembolic disease, ○ Somatosensory evoked response testing:
• Large volume of residual urine fibrocartilaginous emboli monitors afferent pathways of spinal cord
• Bladder expression may be easy or difficult ○ Peripheral nervous system disease ○ Cross-sectional imaging:
(depending on sphincter tone, obstruction). ■ Neuropathy ■ MRI: provides detail of neural and
○ LMN (sacral lesion or peripheral nervous ■ Dysautonomia surrounding tissues
system): flaccid bladder, anus, tail ■ Myopathy ■ CT: provides detail of spinal column
○ UMN (suprasacral lesion): turgid bladder, ■ Neuromuscular junction • Contrast radiography
perineal tone intact ❏ Myasthenia gravis ○ Retrograde urethrography (p. 1181):
○ Detrusor muscle atony (primary muscle): ❏ Botulism evaluate for obstructive patterns
flaccid bladder, perineal tone intact • Hypotonia from overdistention • Abdominal ultrasonography may reveal
○ Neurogenic non-neurogenic cause for urine retention
Etiology and Pathophysiology ■ UMN lesions (suprasacral: L7 to pons) (e.g., mass).
• LMN dysfunction disrupts parasympathetic ○ Non-neurogenic • Cystoscopy and urethroscopy (p. 1085): identi-
control of detrusor muscle (p. 871). ■ Inability to ambulate or posture for fies masses causing urethral obstruction
○ Intramural bladder weakness, causing urination, leading to urine retention • Urodynamic testing
inability to contract and empty normally (e.g., pain, pelvic fracture, inflamma- ○ Cystometry: determine bladder contractile
and completely tion, confinement/behavior) function
○ Lesions in sacral spinal cord, sacral nerves, ■ Urethral obstruction causing overdisten- ○ Urethral pressure profile: evaluate urethral
or pelvic plexus tion (e.g., calculi, intraluminal or tone
○ Internal urethral sphincter tone may be extraluminal mass) ○ Leak point pressure measurement: evaluate
retained because sympathetic innervation ■ Infiltrative diseases (inflammatory, urethral resistance
(hypogastric nerve) is not affected by sacral neoplasm)
spinal cord lesions. TREATMENT
• Severe UMN lesions (L7 to pons) may lead Initial Database
to loss of voluntary micturition and resultant • Residual urine volume increased (normal, Treatment Overview
bladder overdistention. < 0.2-0.4 mL/kg in dogs, or < 10 mL in Management of bladder atony is contingent
○ Disinhibition of sympathetic innervation dogs and < 2 mL in cats). Urinary bladder on treating the underlying condition. Bladder
may increase urethral sphincter tone. catheterization may allow detection of emptying is important in restoring bladder wall
• Non-neurogenic bladder atony results from urethral obstruction. function. Empirical pharmacologic therapy is
urethral outflow obstruction or pelvic disease • Rectal examination begun at the low end of the dosage range and
(i.e., pain, fractures). ○ Anal tone adjusted based on observed response. UTI is
○ Bladder overdistention disrupts tight junc- ■ LMN lesion: decreased or absent a common sequela to urine retention and may
tions between detrusor smooth muscle fibers. ■ UMN or non-neurogenic lesion: present be difficult to eliminate while bladder function
○ Disruption inhibits the wave of excitation ○ Urethra/prostate: possible obstruction, remains defective.
between myofibers, resulting in a flaccid mass effect
bladder. • Neurologic examination and neuroanatomic Acute General Treatment
localization • Urinary bladder catheterization
DIAGNOSIS ○ Complete neurologic examination (p. ○ Indwelling urinary catheter (closed-
1136), including perineal and bulbocav- collection system)
Diagnostic Overview ernosus reflex, tail tone, and sensory testing ○ Intermittent catheterization has a lower
Bladder atony is often secondary to an underly- ■ UMN lesion (usually T3 to L3): sacral risk of inducing UTI than indwelling
ing condition affecting function of the urinary reflexes intact catheters.
bladder and causing urine retention. Diagnosis ■ LMN lesion (L7 to coccygeal region; • Urethral sphincter relaxation
begins with confirmation of the historical peripheral nerves): decreased or absent ○ Smooth muscle relaxation (alpha-
problem and is based on determining the reflexes antagonists)
localization (neurogenic versus non-neurogenic) • Routine blood tests ■ Prazosin: dogs: 1 mg/15 kg PO q
of the primary disease. The physical and neu- ○ CBC: unremarkable 8-12h; cats: 0.25-0.5 mg/CAT PO q
rologic examinations can inform an anatomic ○ Serum biochemistry profile: unremarkable 12-24h. Side effects: hypotension,
or neurologic differential diagnosis. (with urethral obstruction, may reflect mild sedation. Contraindications: see
postrenal azotemia, hyperkalemia) phenoxybenzamine.
Differential Diagnosis ○ Urinalysis, urine culture, and susceptibil- ■ Phenoxybenzamine: dogs: 5-15 mg/DOG
• Hypotonia from LMN disease ity: secondary urinary tract infection PO q 12-24h; cats: 1.25-5 mg/CAT
○ Sacral spinal cord, cauda equina, or nerve (UTI) common PO q 12h. Onset of action takes up
root lesions • Abdominal radiography: distended bladder; to 4 days. Side effects: hypotension,
Degenerative: intervertebral disc hernia- possible evidence of vertebral, pelvic, tachycardia, increased intraocular pres-
■
tion, degenerative lumbosacral stenosis prostatic disease, or urethral calculi sure. Contraindications: cardiovascular
Anomalous: vertebral malformation disease, glaucoma, kidney disease.
■
Neoplasia, including extradural (primary Advanced or Confirmatory Testing Brand-name product (Dibenzyline
■
bone, metastatic [prostatic carcinoma, • Neurodiagnostic testing 10-mg capsules) is cost-prohibitive;
lymphoma]), intradural extramedullary ○ Electromyography (see www.Expert USP-grade powder for compounding
(meningioma, nerve sheath tumor), Consult.com): denervation potentials is more cost-effective.
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