Working up FLUTD (Proceedings)
FLUTD refers to a spectrum of diseases that result in pollakiuria, hematuria, stranguria, dysuria and/or periuria in the cat. Common causes of these clinical signs include urolithiasis, urethral plugs and neoplasia (most commonly, transitional cell carcinoma). Urination in inappropriate places (periuria) may be due to behavioral issues and must be investigated with a thorough history and description of the cat's home environment. Although bacterial infections are common in the canine population, they are an uncommon cause of FLUTD in cats. Feline idiopathic cystitis (FIC) or idiopathic FLUTD (iFLUTD) is characterized by chronic voiding signs (dysuria, hematuria, pollakiuria and/or inappropriate urination), sterile urine with no cytologic abnormalities and evidence of glomerulations (pinpoint submucosal hemorrhages) on cytoscopic examination. It is ultimately a diagnosis of exclusion and is one of the more common causes of FLUTD in cats < 8 years of age.
Possible etiologies for idiopathic FLUTD
Several etiologies have been suggested for iFLUTD. One hypothesis suggests that alterations of bladder innervation and depletion of the glycosaminoglycan (GAG) protective layer exposes and/or up-regulates of C-pain fibers. This, in turn, results in release of substance P which has multiple effects on the bladder urothelium and may account for a vicious cycle of pain and dysuria. Bacterial infections are extremely uncommon in cats under 10 yrs of age, and given the normal age group of cats presenting with iFLUTD (young to middle-aged), it is also an unlikely cause of FLUTD in this age group. The majority of bacterial infections detected in cats are iatrogenic (catheterization) or secondary to an instigating cause (neoplasia, urolithiasis, congenital defect). Cats older than 10 years have a higher incidence of UTIs, perhaps related to renal insufficiency and decreased urine specific gravity. Some studies have identified Mycoplasma and Ureaplasma in feline urine, but a link to the etiology of iFLUTD has not been established. Another study identified DNA from gram-negative bacteria using PCR from cats with iFLUTD that had negative bacterial culture, suggesting perhaps cell wall deficient bacteria. Bovine herpesvirus-4 has been shown in an experimental setting to induce iFLUTD and BHV-4 has been isolated in some cats with iFLUTD. Likewise, calicivirus-like particles have been detected in cats with urethral plugs. Despite some supporting evidence for each of these infectious and neurogenic inflammation hypotheses, no single cause has been consistently identified in all cats with iFLUTD.
Working up FLUTD
Keeping in mind that FLUTD is an umbrella of diseases, each cat presenting with stranguria, pollakiuria, inappropriate urination or partial/complete obstruction should be approached similarly. iFLUTD is a diagnosis of exclusion. A typical workup for these cats includes:
Urinalysis: cystocentesis is preferred, but may be difficult because these cats often have small irritated bladders. Free-catch samples can be helpful for cytologic analysis, but positive cultures obtained from free-catch samples should be interpreted with caution. A comparison of free-catch- and cystocentesis-obtained samples may be useful in cases of transition cell carcinoma that is located within the urethral and may not be visualized on ultrasound. In this latter example, there may be no transitional cells in the cysto sample, but many transitional cells in the free-catch sample.
Urine culture: Especially in cats > 10 years and those cats with previous catheterizations. A urine culture can also confirm sterile urine in the face of pyuria that is typical of iFLUTD.
Complete blood count: To evaluate for evidence of inflammation or non-regenerative anemia that would implicate an upper urinary tract issue. Lower urinary tract inflammation should not cause a systemic inflammatory leukogram.
Biochemistry panel: To identify renal or other co-existing diseases that might be contributing to the clinical signs.
Radiographs: To rule out radiodense urolithiasis. The most likely offenders in cats are calcium oxalate followed by struvite, both radiodense. The increased prevalence of calcium oxalate stones relative to struvite stones that has taken place in the last 10 or so years is likely associated with the attention to ash content and, more importantly, urinary pH effects in commercial cat foods.
Ultrasound: To obtain a urine sample in some cases of very small irritated bladders; to rule-out the more uncommon non-radiodense stones; to assess for bladder abnormalities or presence of tumor; to assess renal architecture.
Contrast cystourethrogram if urethral disease or diverticuli are suspected and catheterization is possible.