Several acronyms are used to describe the causes of lower urinary tract signs, especially those that refer to the idiopathic syndrome. FLUTD is commonly used to refer only to the idiopathic syndrome in cats. Technically, however, FLUTD encompasses all causes of lower urinary tract signs, including urolithiasis, urinary tract infection (UTI), reflex dyssynergia, trauma, congenital abnormalities, neoplasia, and sterile or idiopathic feline lower urinary tract disease (iFLUTD). Additional terms include feline urinary, or urologic, syndrome (FUS) and feline interstitial or idiopathic cystitis (FIC). Some authors contend that interstitial cystitis should be reserved for cats in which cystoscopic evidence of mucosal disruption has been confirmed.¹ In this article, I use iFLUTD to emphasize that the disease entity discussed is idiopathic and LUTS (lower urinary tract signs) to refer to the nonspecific signs associated with any lower urinary tract disease.

Non-iFLUTD causes of LUTS—including urolithiasis, UTIs, neoplasia, trauma, and congenital abnormalities—must be ruled out before iFLUTD can be diagnosed. A diagnosis of iFLUTD can refer to a single episode of LUTS or chronic, recurrent clinical signs with or without urethral obstruction. Obstructive iFLUTD is life-threatening, requiring in-hospital management or surgical intervention. Detailed management of cats with obstructive iFLUTD has been described elsewhere in the literature.^2,3 With either obstructive or nonobstructive iFLUTD, owners may even consider euthanasia in cases of chronic recurrent episodes because of their cats' poor quality of life and the expense and frustration of treating affected cats. In an effort to help affected cats and their owners, this article reviews the proposed causes, typical clinical signs, diagnostic testing, and medical and environmental management of cats with nonobstructive iFLUTD.

It is important to understand the proposed causes of iFLUTD because they have led to a variety of therapies targeting those mechanisms. Many of the causes that have been suggested for iFLUTD have been extrapolated from research investigating interstitial cystitis in women. As more studies are conducted, further evidence for the cause or causes of iFLUTD may emerge, but based on the available body of knowledge, the disease appears to be multifactorial.

Infection

Bacterial cystitis leading to pain, inflammation, and LUTS is one cause to consider. Most studies investigating the general causes of LUTS report a low overall incidence (< 3%) of bacterial UTIs.^1,4,5 In one large retrospective study, UTIs were identified in 12% of cats with LUTS, most of which occurred in cats > 10 years of age.⁶ However, a recent study evaluating cats in Norway with LUTS showed that 23% of cats with either obstructive or nonobstructive iFLUTD had positive culture results based on samples collected by either cystocentesis or midstream free-catch.⁷

Since most studies have been unable to demonstrate positive culture results in cats with iFLUTD, stealth organisms (those that are difficult to identify through conventional diagnostic testing) have been implicated as causative agents of iFLUTD. Ureaplasma and Mycoplasma species have been associated with UTIs in several species, including people, rodents, sheep, dogs, and cats; because they have no cell wall, these organisms are difficult to culture.⁸ However, in a recent study in which 91 urine samples from cats with recurrent iFLUTD and negative bacterial culture results were evaluated by using PCR assays to detect Mycoplasma and Ureaplasma species, the organisms were not identified.⁸ Viral particles such as bovine herpesvirus-4 and calicivirus have also been implicated.^9,10 Recently, two novel feline caliciviruses were identified in two of 40 cats with iFLUTD,¹¹ but their significance in iFLUTD is unknown.