Page 193 - Problem-Based Feline Medicine

11 – THE CAT STRAINING TO URINATE 185

luria with amorphous urates and phosphates is thra. To minimize back leakage, digital pressure
occasionally seen. around the catheter and urethra can be applied or
● Urine sediment containing struvite crystals balloon-tipped catheters (4 or 5 French) can be
(three- to six-sided colorless prisms) suggests that used to occlude the urethra. Radiographs are
the urolith is struvite in composition. taken during the infusion of the last portion of
● Urine sediment containing calcium oxalate dihy- the bolus dose.
drate (colorless envelopes with dipyramidal or
Ultrasonography.
octahedral form) or monohydrate crystals (small
● Abdominal ultrasonography can be used to identify
spindles or dumbbells) suggests that the urolith is
radiodense and radiolucent cystic uroliths, as
calcium oxalate in composition.
well as soft tissue masses.
● Ammonium biurate crystals (yellow-brown
spherulites; thorn apples) are common in cats with Blood tests (biochemistry).
portosystemic vascular anomalies, however urate ● Elevated serum urea and creatinine levels suggest
uroliths are uncommon. Rarely urate uroliths also renal involvement.
occur due to tubular disease (cat has no signs of ● Elevated liver enzymes and/or low urea levels sug-
liver disease and normal pre- and post-prandial bile gest liver dysfunction. Typically cats with ammo-
acids). Urate crystals associated with tubular dis- nium biurate uroliths associated with portosystemic
ease appear different from biurates, and are com- shunts have reduced serum urea levels, increased
posed of uric acid or sodium acid urate. serum uric acid and bile acid levels and hyperam-
● However, crystal type in urine and urolith com- monemia.
position can be different. ● Hypercalcemia may suggest a calcium-containing
● Uroliths found in alkaline urine are likely to be stru- urolith.
vite or calcium phosphate (amorphous or long thin
Urolith analysis.
prisms).
● Urolith analysis provides valuable information that
● Urinary tract infections are usually absent (<2%).
can be used in therapy to prevent the recurrence of
● Hypercalciuria may occur with calcium containing
urolithiasis.
uroliths.
● Crystallographic, X-ray diffraction and infrared
Radiography. spectroscopy techniques are preferable to qualitative
● Plain abdominal radiographs may detect radiodense chemical analysis (Oxford Stone Analysis Kit).
uroliths in the kidneys, bladder or urethra. A proper quantitative analysis gives all the min-
– Radiodense uroliths contain calcium salts, eral components of the urolith by percentage and
such as calcium oxalate. by location (surface, middle and center).
– Struvite uroliths may contain calcium and Prevention therapy is based on the mineral com-
become slightly radiodense. position of the center of the urolith as precipitation
● Double-contrast cystography can be used to of the central mineral initiates urolith formation.
detect radiolucent uroliths. The technique
involves instilling, via a urinary catheter, 1–2 ml Differential diagnosis
of water-soluble iodinated contrast material (pos-
itive contrast) into the urinary bladder, followed Infectious cystitis/urethritis is differentiated on the
by a slow infusion of carbon dioxide or nitrous presence of bacteriuria and a positive culture.
oxide gas (negative contrast), sufficient to distend
Idiopathic LUTD tends to occur in young adult cats.
the bladder (approximately 30 ml). Fatal air
embolism can occur in cats with hematuria when
Treatment
air is used.
● Retrograde contrast urethrography. The tech- Uroliths can be removed by medical dissolution or sur-
nique involves infusing, as a bolus, 5 ml of posi- gical resection. The type and location of the urolith, the
tive contrast material through an open-ended severity of the clinical signs, the anesthetic risk, con-
urinary catheter positioned in the distal ure- current diseases, the sex and age of the cat, and the