A diagnosis of interstitial cystitis in people and cats requires identification of the presence of characteristic (although non-specific) sub-mucosal petechial hemorrhages—referred to as glomerulations—by cystoscopy, though the diagnostic value of this criterion is under debate. It is likely that the term idiopathic or interstitial cystitis in cats will be supplanted by more specific diagnoses as we improve our understanding of this frustrating syndrome. Results of studies over the past decade indicate that idiopathic cystitis in cats is the result of complex interactions between the bladder, nervous system, adrenal glands, husbandry practices, and the environment in which the cat lives (further detailed under pathophysiology).

Differential diagnosis

Dysuria, stranguria, pollakiuria, macroscopic hematuria, and urinating in places other than the litter box (inappropriate urination or periuria) are non-specific signs that, individually or in some combination, cause clients to bring their cats to a veterinarian due to apparent nonobstructive problems with the lower urinary tract regardless of the underlying cause. In cats less than 10 years of age, idiopathic cystitis accounts for clinical signs of irritative voiding in 60 to 70% of cats. Urolithiasis is encountered in 10 to 20% of cases with most, being associated with either calcium oxalate or struvite. About 10 % may have an associated structural abnormality such as urachal diverticulum or urethral stricture, another 10% have what appears to be a behavior disorder, less than 2 % of cases will be associated with urinary infection, and less than 1% can be expected to have bladder or urethral neoplasia. In cats older than 10 years of age at first presentation, only about 5% can be expected to be idiopathic. More than half of cats in this age category will have bacterial urinary tract infection, either alone or in association with urolithiasis. Many of these cats with positive quantitative bacterial cultures will have renal disease and sub-maximally concentrated urine.

Idiopathic cystitis affects males and females equally, although neutered males and females are at increased risk compared to their intact counterparts. An affected cat typically is 1 to 10 years of age (peak risk 2-6 years), spends all or nearly all of its time living indoors with humans, is expected to use a litter pan for urination and defection, and eats 75 to 100% dry food. Obesity and a variety of other comorbid conditions may be associated with idiopathic cystitis. Owners sometimes note that affected cats are unusually nervous, fearful, or aggressive, and are overreactive to their environment compared to healthy cats. Cats with access to the outdoors still can be affected, especially when the cat population in the outdoor area is dense. Abdominal palpation may reveal pelvic organ pain and/or thickening of the bladder wall in some affected cats. The bladder is usually small during active bouts of cystitis. The rest of the examination is often normal. Rarely, barbering of hair in the caudal abdomen may represent referred pain. It is our impression that cats with IC have more heart murmurs and gallop rhythms than cats with other disorders.

Urinary tract imaging is recommended for all cats with recurrent LUTS. Survey radiographs are helpful to identify radiodense calculi such as calcium oxalate or struvite, which usually are observed if ≥ 2-3mm in size. In those cats with multiple recurrences or persistence of clinical signs, advanced urinary imaging should be pursued to exclude radiolucent calculi and anatomical defects if the survey radiographs were normal. Abnormalities that can be identified during double-contrast cystography include focal or diffuse thickening of the bladder wall, permeation of contrast agent into the bladder wall or through the bladder and into the abdomen, and filling defects in the contrast pool (blood clots and cellular debris). Ultrasonography (ULS) can be a useful, less invasive method of imaging than contrast urethro-cystography. The proximal urethra can be examined with ULS, but ULS is not a good method to image the urethra, as most of the urethra cannot be examined. Cystoscopy (uroendoscopy), which provides direct visualization of the internal surface of the bladder, is available at some referral centers. Excellent evaluation of the urethra and bladder lumen usually is possible in female cats weighing at least 3 kg using a rigid pediatric cystoscope. The bladder of idiopathic cystitis cats will often display a varying degree of increased vessel density and tortuosity, edema, and sub-mucosal petechial hemorrhages (glomerulations). Increased number or size of glomerulations and increasing edema can be observed when higher bladder filling pressure (~80 cm water) is used during the scoping, findings that do not happen in cats with normal bladders.