Page 192 - Problem-Based Feline Medicine

184 PART 4 CAT WITH URINARY TRACT SIGNS

occur. Post-surgically, urethral strictures and/or incon- Hypercalcemia (primary hyperparathyroidism,
tinence have been reported, but are uncommon follow- pseudohyperparathyroidism, idiopathic, hypercalcemia
ing uncomplicated surgery. Urethrostomy may and vitamin D intoxication) results in hypercalciuria,
predispose to ascending urinary tract infection. which has been associated with calcium oxalate
urolith formation. However, most cats with calcium
oxalate uroliths have normal serum mineral levels.
UROLITHIASIS**
Congenital portovascular anomalies and renal tubu-
Classical signs lar reabsorptive defects have been associated with
purine (urate) uroliths. Urate uroliths consist of either
● Blood-tinged urine (hematuria).
ammonium biurate (which occur with porto/vascular
● Frequently seen trying to urinate
anomalies), uric acid or sodium acid urates (occur with
(pollakiuria).
tubular defects). Predisposed cats fed a high purine diet
● Spends more time in litter box.
(e.g. liver) and producing concentrated, acidic urine are
● Straining to urinate (dysuria).
at a greater risk of producing purine uroliths.
● Cat may urinate in inappropriate places.
Cystinuria due to proximal renal tubular dysfunction
can predispose to cystine urolith formation.
Pathogenesis
Uroliths, especially those in the bladder, can cause
Urolithiasis in cats is uncommon and represents
lower urinary tract disease.
less than 5% of cats presented with hematuria and
dysuria. The formation of small uroliths can lead to urethral
obstruction, especially in male cats.
Urolithiasis is the formation of stones called uroliths
(calculi) in the urinary tract.
Clinical signs
Uroliths are made up of crystalloid with very little
organic matrix, and although a particular chemical Mainly seen in middle-aged adult cats.
type usually predominates, the chemical composition
There appears to be no sex or breed predisposition.
of the urolith can be mixed.
● The main chemical composition of uroliths Most cystoliths are asymptomatic.
reported in cats, include magnesium ammonium
Persistent or recurring cystitis may occur and present
phosphate (struvite; 42%), calcium oxalate
as increased frequency of urination, straining to urinate
(46%), purine (uric acid and urates; 6%), calcium
or increased time spent in the litter box or urinating in
phosphate (<1%) and cystine (<1%).
inappropriate places.
● Each chemical type should be considered a separate
disease process. Hematuria varies from microscopic hematuria
● The incidence of struvite uroliths appears to be (>5 RBC/hpf) to gross hematuria.
decreasing while calcium oxalate uroliths are
Urethral obstruction may occur occasionally, more
increasing. This is thought to be due to the
commonly with calcium oxalate, urate or cystine
increased use of acidifying diets in cats.
uroliths than with struvite uroliths.
Urolithiasis is not a single disease entity, but rather the
end result of one or more physiological and/or patho-
Diagnosis
logical processors, interrelated with some predispos-
ing factor(s), such as urine pH and concentration, Physical examination. Cystic uroliths are usually dif-
excessive excretion of endogenous crystalloid-form- ficult to palpate (<10%) because most are flattened
ing substances (uric acid, amino acid cystine), exces- disc-shape and few in number.
sive mineral intake and genetic factors.
Urinalysis.
Unlike the dog, struvite uroliths in cats are usually not ● Most uroliths and crystals in a urine sample are cal-
associated with urinary tract infection. cium oxalate or struvite, although heavy crystal-