5.3 LOWER URINARY TRACT: DISORDERS OF URINATION
Inappropriate urination is commonly reported to occur in older dogs and cats that
have previously been house trained, and this behaviour change is frequently a reason
for owners seeking euthanasia (Ruehl W.W., personal communication).
In some individuals the micturating reflex may be abnormal due to impaired neuromuscular
function (either locally or in the CNS) with loss of conscious voluntary control
of urination (Oliver 1987). In other cases the individual may be exhibiting behavioural
changes due to senile changes in the CNS (see Chapter 3).
Urinary incontinence is common in old bitches and has been linked to ovarohysterectomy
by some authors but the evidence from long-term studies have still to confirm such
an association. Failure of the urethral sphincter mechanism is the underlying problem
and some cases respond to aestrogen therapy (stilboestrol - orally at 0.1-1 mg daily
for 3-5 days followed by weekly treatment has been recommended). Urethral tone can
be improved by administering µ-adrenergic stimulants
(with or without concurrent use of oestrogens) and phenylpropanolamine is currently
recommended at 1.5 mg/kg b.i.d. or 1 mg/kg t.i.d.
Involuntary voiding of urine may be primary (associated with a neuromuscular disorder of the
bladder) or secondary to a primary condition such as urinary tract infection or neoplasia.
Although rare, primary detrusor muscle disorders may respond to anticholinergic drugs,
e.g. propantheline at a dose rate of 7.5-15mg t.i.d.
Any condition that causes bladder wall irritability (e.g. cystitis) can lead to frequent
micturition which can easily be confused with incontinence by owners.
Urinary incontinence can be a sequel to urine retention for example due to urolithiasis,
or spinal injury or disease.