Page 203 - Problem-Based Feline Medicine

12 – THE INCONTINENT CAT 195

Incontinence, pollakiuria or nocturia associated
INTRODUCTION
with an empty bladder reflect storage disorders
(reduced bladder capacity, hyperactivity of the detrusor
MECHANISM? muscle, urethral incompetence).
The incontinent cat intermittently or continuously In contrast, urine retention with overflow, or incom-
dribbles urine because it has lost voluntary control plete voiding and a distended bladder indicate emp-
over urination. tying disorders (detrusor atony, urethral obstruction).
Cats that urinate at inappropriate times or in inappro- Following spontaneous bladder emptying there
priate places need to be differentiated from incontinent should be less than 0.5 ml of urine remaining in a
cats through history taking and clinical examination. normal cat.
Maintenance of urinary continence in the cat depends
on normal lower urinary tract anatomy and an WHERE?
intact sympathetic, parasympathetic and somatic
Lower urinary tract (lower ureter, urinary bladder, urethra).
nervous system.
● Anatomical abnormalities can bypass (ectopic
WHAT?
ureter) or negate (urethral hypoplasia) neuromuscu-
lar control mechanisms. Urinary incontinence in cats is uncommon. In juvenile
Continence during the filling stage is maintained via cats, it is more likely due to a congenital abnormality
the following mechanisms: sympathetic stimulation (ectopic ureter): in the adult cat it is more likely neu-
(hypogastric nerve) during the filling phase causes rologic in origin. Secondary urinary tract infections are
the body of the bladder (detrusor muscle) to relax common.
(β-receptors) and the bladder neck and urethral smooth
muscles to contract (α-receptors). DISEASES CAUSING SIGNS OF
● Additional urethral resistance is supplied by the ure- URINARY INCONTINENCE
thral striated muscle, which reflexively contracts
and is under voluntary control (pudendal nerve).
HYPOCONTRACTILE BLADDER***
The emptying phase occurs as follows: Parasympathetic (DETRUSOR ATONIC/HYPOTONIC
stretch receptors in the detrusor muscle detect blad- BLADDER)
der fill, and when the threshold of bladder capacity is
reached, they discharge impulses via the sacral spinal Classical signs
cord to the pons in the brain stem, where a detrusor
● Dribbling urine.
response is integrated.
● Distended urinary bladder.
Efferent motor impulses descend the spinal cord to the ● ± Hindquarter ataxia or paresis.
detrusor muscle via the pelvic nerve causing detrusor ● ± Tail paralysis.
muscle contraction.
● Simultaneously, inhibitory interneurons are acti-
vated in the sacral spinal cord, which synapse on Pathogenesis
pudendal motor neurons, resulting in a relaxation
Hypocontractile bladder can occur due to detrusor dys-
of the external urethral sphincter.
function or secondary to prolonged bladder distention.
Once the bladder is empty, parasympathetic activity
Detrusor dysfunction.
ceases and the sympathetic and pudendal nerves are no
● Lesions cranial to the sacral spinal cord may
longer inhibited.
disrupt sensory and motor pathways to the urinary
Detrusor muscle relaxation and urethral sphincter con- bladder. This results is an upper motor neuron
traction returns and the filling phase begins again. bladder: