Diagnosis

4. Diagnosis

History and Clinical Signs

Regardless of cause, cats with FLUTD present with hematuria (macroscopic and/or microscopic), dysuria, stranguria, pollakiuria, inappropriate urination (periuria or signs of irritative voiding outside of the litter box), or partial or complete urethral obstruction (Kruger et al., 1991; Osborne et al., 1996a). Male cats may be observed to lick the tip of the penis. Cats are often observed to spend longer amounts of time than normal in the litter box attempting to urinate or are observed to pass small amounts of urine frequently. Restless behavior or excessive grooming of the caudal abdomen may indicate discomfort.

Urinary tract obstruction may occur suddenly or over a period of weeks. Complete obstruction is characterized by depression, anorexia, lethargy, dehydration, hypothermia, and vomiting. In severe cases the bladder may rupture providing a transient relief of signs followed rapidly by the development of peritonitis and death.

Physical Examination

A complete physical examination should be performed in any cat presenting with FLUTD. Special attention should be paid to the hydration status, bladder, and external urethral orifice. The bladder should be palpated to evaluate its size (degree of distension), shape, contours, thickness of the bladder wall, intramural or intraluminal masses (tumors, uroliths, clots), or grating within the bladder lumen. Most uroliths cannot be detected by abdominal palpation (Osborne et al., 2000). Palpation frequently elicits an expression of pain such as crying, resistance to further abdominal palpation, straining to urinate, or passage of a few drops of blood-tinged urine. The penis, prepuce, or vulvar area should be examined for urethral abnormalities and evidence of blood, mucus, or mineral crystals.

In cats with obstructive FLUTD, the bladder is distended, turgid, and painful. In obstructed cats, the tip of the penis may appear discolored because of inflammation and trauma from licking or because of the presence of a urethral plug (Figure 8). Urethral obstruction is a medical emergency that requires immediate relief of the urethral obstruction. The patient's fluid, electrolyte (especially hyperkalemia), and acid-base status should be assessed and appropriate therapeutic maneuvers initiated (see below in treatment section).

Figure 8. Feline urethral plug. A cream to straw-colored urethral plug may be visualized protruding from the urethra. Struvite crystals are the predominant crystals found. (© Andrew Moore (CVUC)).

Laboratory Evaluation

In the non obstructed cat, the initial evaluation should include a urinalysis with sediment examination, urine culture, and abdominal imaging. A complete blood count can be conducted; however, it is nearly always normal. A comprehensive biochemical profile should be obtained from cats that are sick or have urethral obstruction. In cats with urate urolithiasis, serum urea nitrogen may be low in cases of portosystemic shunts or liver failure; some cats with calcium oxalate urolithiasis have hypercalcemia.

Urine for analysis may be collected by the owner using a special litter or in the clinic by obtaining a midstream sample during natural voiding, catheterization, or cystocentesis. Manual expression should be avoided as iatrogenic hemorrhage/trauma can be a significant consequence. In addition, in the rare occasion where infection is present, retrograde ascension from the bladder to the kidney and the development of pyelonephritis is possible.

The method of collection will influence the diagnostic results and their interpretation. Cystocentesis is preferred because it prevents contamination of the urine sample by the urethra or genital tract. It is minimally invasive, well tolerated, and safe so long as proper technique is used to prevent iatrogenic urinary tract trauma or infection. The main contraindications to cystocentesis are insufficient volume of urine in the urinary bladder, patient resistance to restraint and abdominal palpation, and coagulopathy or bleeding disorders. Cystocentesis should not be performed if the bladder cannot be palpated.

Urinary catheterization may be performed for:

• Diagnostic indications: collection of urine for analysis, detection of urethral obstacles (e.g., uroliths, tumors), and instillation of contrast medium for radiographic studies
• Therapeutic indications: relief of urethral obstruction and facilitation of surgery of the bladder, urethra, or surrounding structures.

The time of day at which the urine is collected should be recorded. In addition, the owner should be questioned on when the cat last ate and how stressed the cat was coming into the hospital. The urine pH is generally the most acidic first thing in the morning, prior to the animal eating. The pH may be higher if the urine is collected in the post prandial period (anywhere from 2 - 6 hours after a meal). Once the urine pH is above 6.5, struvite crystals can form. If the cat was stressed by transportation to the clinic, hyperventilation may have occurred and this too can raise the urine pH above 6.5 resulting in the appearance of struvite crystals (Buffington & Chew, 1996a).

The urine sample should be collected into a sterile collection container. If culture is to be performed, a portion of the urine should be refrigerated immediately in an airtight sterile container. For sediment analysis, the urine should not be refrigerated but is kept at room temperature and covered to avoid light exposure. Analysis should be performed on fresh urine (within 15 - 60 minutes of collection); otherwise struvite and calcium oxalate crystals can form (Albasan et al., 2003). Physical properties of the urine, chemical properties of the urine and examination of urinary sediment should all be determined. Abnormalities consistent with FLUTD that may be noted on urinalysis and sediment examination include hematuria, proteinuria, pyuria, and crystalluria (struvite, amorphous phosphates, urate, calcium oxalate, cystine and xanthine (Figure 9 - Figure 12).

Figure 9. Struvite urinary crystals. (© Waltham Centre for Pet Nutrition).

Figure 10. Calcium oxalate urinary crystals. (© Waltham Centre for Pet Nutrition).

Figure 11. Ammonium urate urinary crystals. (© Waltham Centre for Pet Nutrition).

Figure 12. Cystine urinary crystals. (© Waltham Centre for Pet Nutrition).

The identification of crystals in the urine is dependent on the urine pH, temperature, and specific gravity. However, it is important to note that the presence of struvite or calcium oxalate crystals in the urine does not necessarily signify a problem. A few crystals in highly concentrated urine generally have less significance than a few crystals in dilute urine (Laboto, 2001). Absolutely fresh urine must be examined as crystals may form in urine that is allowed to stand and cool prior to examination (in-vitro crystallization) (Table 2). The presence of crystals observed in stored samples should be validated by reevaluation of fresh urine (Albasan et al., 2003).

Quantitative bacterial culture of the urine is indicated to conclusively diagnosis urinary tract infection. Urine should be obtained by cystocentesis to prevent iatrogenic bacterial contamination and submitted for culture within 30 minutes of collection. If this is not possible, urine should be refrigerated. Once positive identification of the organism is obtained, antimicrobial sensitivity should be performed to guide appropriate antimicrobial therapy.

Diagnostic Imaging

Diagnostic imaging techniques include survey radiographs, ultrasound, contrast radiography (excretory urography, cystography, urethrography), computed tomography, and magnetic resonance imaging (Samii, 2003).

• Survey radiographs are used to screen for changes in the size, shape, position, or radiodensity of the urinary tract. It is important to radiograph the entire urinary system including the perineal urethra to ensure no abnormalities are overlooked (Figure 13). In some cases, a cleansing enema may be needed to ensure adequate visualization of the urinary system. In cats with FIC, the bladder may appear thickened and non-distensible on radiographic examination (Figure 14).

Figure 13. Lateral radiograph of a male cat with urolithiasis. The image indicates numerous small, radio-dense uroliths in the urethra of a male cat presenting with obstructive feline lower urinary tract disease. (© Dr Brian Crabbe, Port Elgin, Ontario, Canada).

Figure 14. Lateral radiograph of a two year old cat with feline idiopathic/interstitial cystitis. Note the bladder wall appears thickened and non-distensible. (© Gagemount Animal Hospital, Hamilton, Ontario, Canada).

• Ultrasound allows assessment of intra-luminal abnormalities not seen on survey radiographs, determines what area is affected and to what extent, and provides information regarding tissue composition, i.e., solid versus cystic lesions.
• Positive contrast cystography is used to determine bladder location, rupture, diverticulae, and fistulas.
• Double contrast cystography is used to evaluate the mucosal surface of the bladder and luminal contents. A good quality double contrast study requires only a small volume (1 - 2 mL) of positive contrast medium. It is important to palpate the bladder as it is being filled with contrast in order to monitor the degree of distension and to avoid over inflation. The bladder should be well distended with the negative contrast medium and a small volume of positive contrast (the so called contrast puddle) should lie on the dependant surface of the bladder lumen. Radiolucent uroliths are identified as filling defects in the contrast puddle. Blood clots are identified as irregular filling defects either at the margin of the contrast puddle or adherent to the mucosal surface. Recognition of small alterations of the contour of the mucosal surface is an important clue in the diagnosis of both cystitis and tumor, but can be artifactual as a result of incomplete filling of the bladder. Urethrography is used to examine the urethra.

Uroendoscopy

Endoscopy of the urethra and bladder is now possible using a flexible fiber optic scope in male cats and a rigid human pediatric cystoscope in female cats (Chew et al., 1996; McCarthy 1996). The mucosal surface of the bladder of cats with FIC displays characteristic findings of submucosal petechial hemorrhages (glomerulations) during cystoscopy following bladder distension to 80 cm H20 (Chew et al., 1996; Buffington et al., 1999a) (Figure 15).

Figure 15. Endoscopic appearance of the bladder mucosa in a cat with lower urinary tract disease. The endoscopy demonstrates glomerulations consistent with feline idiopathic/interstitial cystitis. (© Compliments CA Buffington and DJ Chew, Columbus, Ohio).

Surgery

When surgery is performed for exploration, biopsy or urolith removal, the bladder should be fully opened (Figure 16a and Figure 16b). Because many feline uroliths are very small, complete surgical removal of all uroliths may be difficult and post surgical radiography should always be performed to ensure all uroliths have been removed (Lulich et al., 1993a). Failure to remove all uroliths at the time of cystotomy is common and seems to be more likely with calcium oxalate uroliths. Lulich et al. (1993a) reported that calcium oxalate uroliths were incompletely removed in 20% of cats.

Figure 16a. Multiple calcium oxalate calculi in a cat bladder. Note the bladder has been opened fully to allow for complete removal of all uroliths, a number of which are embedded in the bladder mucosa. (© Dr. Anne Sylvestre, Guelph, Ontario).

Figure 16b. Surgical removal of uroliths in the bladder. The bladder of the cat has been entirely opened and the mucosal surface everted to ensure complete removal of uroliths. A post operative radiograph confirmed the complete removal of all of the uroliths. (© Dr. Anne Sylvestre, Guelph, Ontario).

Histopathology

Biopsies of the bladder mucosa of cats with FIC may show relatively normal epithelium and muscularis with submucosal edema and vasodilation; infiltration of inflammatory cells is mild to moderate (Figure 17). Some cats have increased numbers of mast cells; others have erosions, ulcerations or fibrosis of the bladder wall.

Figure 17. Histological appearance of the bladder mucosa of a cat with lower urinary tract disease. Submucosal edema and erosions consistent with feline idiopathic/interstitial cystitis. (© Compliments CA Buffington and DJ Chew, Columbus, Ohio).

Analysis of Urolith Composition

Uroliths may be collected by spontaneous voiding (use an aquarium fishnet to catch the urolith), voiding urohydropropulsion, aspiration into a urethral catheter, via cystoscopy, or surgical removal (Lulich et al., 1992,1993b; Osborne et al., 2000). Uroliths need to be submitted in a clean dry container without preservatives or additional fluids. In many cases, uroliths cannot be identified simply by visual characteristics. All uroliths retrieved should be quantitatively analyzed by specialized laboratories to determine mineral composition of any/all of the 4 layers that may be present (Figure 18). There are 4 techniques available for quantitative analysis including polarizing light microscopy, x-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Accurate identification of the type or types of minerals present in a urolith is paramount in order to apply the appropriate therapeutic and preventative regime.

Figure 18. Illustration of the layers of a urolith. Quantitative analysis allows accurate determination of the mineral composition of any of the four layers that may be present: nidus, stone, shell and surface crystals.

Predicting Urolith Type

Effective treatment and prevention of uroliths depends on knowledge of their mineral composition. Ideally, a urolith should be retrieved and quantitatively analyzed, however, there are a number of factors that can help in predicting urolith composition including signalment (age, sex, breed, Table 3), history of underlying disorders, radiodensity of the uroliths and urine parameters (pH, specific gravity, crystalluria, Table 4). It is important to remember that crystals may or may not be present in the urine sample and the urine sample may contain crystals that differ from the underlying urolith composition (Buffington & Chew, 1999b).