Feline Idiopathic Cystitis

FIC - Feline Idiopathic Cystitis.

It is common for cats to get cystitis (inflammation of the bladder).  One of the more common causes is a disease that is poorly understood. This disease has a lot of different names including: FIC (feline interstitial cystitis or feline idiopathic cystitis), iFLUTD (idiopathic feline lower urinary tract disease), and FUS (feline urologic system). It is sometimes incorrectly called a UTI (urinary tract infection).


FIC causes painful urination.The signs that people notice most commonly are frequent attempts to urinate, small amounts of urine produced at a time, urinating outside the litter box, and blood in the urine.

We don't fully understand why cats get this disease but it is not due to bacterial infection and antibiotics are not helpful.


Discussing cystitis in cats is confusing. This is because words are used differently by different people. This is a list of our use of the words. Beware that other sources may use other definitions.

Crystaluria: Crystals in the urine. 

Cystitis: Inflammation of the urinary bladder regardless of cause.

Dysuria: Difficult or painful urination. This may manifest as squatting to urinate for long periods, making frequent trips to the litter box, urinating outside of the litter box, howling, or a number of other ways.

Hematuria: Blood in the urine. Sometimes the urine still looks yellow and the blood can only be detected microscopically or with chemical tests. Sometimes it looks like pure blood.

House soiling: Urinating or defecating in the house, outside of the litter box. Some veterinarians use the term periuria or inappropriate urination.

Idiopathic: A medical condition with a cause that has not yet been established in the medical literature. 

Stranguria: Straining to urinate. Since cats don't usually make a face or an odd noise when they strain, a lot of times humans don't recognize what they are doing to be straining.

Stress: Psychological stress. This is an internal reaction to usually external stimuli. Anything that causes a cat to become upset, including medicating them, can cause stress.

Urethral Spasm: Inappropriate and painful contraction of the muscle of the bladder / urethral sphincter. Urethral spasms can prevent a cat from being able to urinate or they may cause an unsteady or intermittent stream of urine.

Urinary Obstruction: Anything that obstructs a cat's urethra so that they can't urinate. This is sometimes a "plug" of debris (crystals, blood, etc.) and it is sometimes a urethral spasm. Urinary obstructions are life threatening.  

Causes of FIC

Interstitial cystitis in cats is an idiopathic condition - meaning we don't know what causes is. We do know that stress and obesity are often predisposing factors.

Most cases of FIC resolve without treatment. This can create a lot of confusion in understanding the underlying cause. For example, if a cat with FIC is put on a special diet and gets better, a lot of people conclude that the old diet caused the FIC and that the new diet helped when really, the cat just had a transient, self limiting cystitis. Likewise, if a cat with FIC is put on antibiotics and gets better, it doesn't mean that there was an infection or that the antibiotics were in any way helpful. 

Things that Probably Don't Cause Cystitis in Cats.

There are a a number of things that have been incorrectly described as causing idiopathic cystitis in cats.


Crystals commonly form in a cat's urine when:

  • The urine is concentrated (e.g., from a diet low in moisture / water)
  • The pH of the urine is high (e.g., from a diet high in carbohydrates)
  • The kidneys secrete high levels of minerals (e.g., from a diet high in ash)
  • There is blood in the urine (e.g., when a cat has cystitis)
  • The urine stays in the bladder for prolonged periods (e.g., when a cat is obstructed)
  • The temperature of the urine decreases (i.e., crystals will grow after the urine sample is taken from the cat)

Crystals almost never cause cystitis but are often caused by cystitis.

Under the microscope the crystals look sharp and we used to think that the crystals caused the bleeding. Most experts now agree that crystals don't cause inflammation and bleeding. Inflammation and bleeding cause crystals.

We see a lot of cats with crystals in the urine who have no sign of cystitis.

We don't want crystals in the urine because:

  • They can be a sign of a problem (e.g., lack of water intake or too much carbohydrate in the diet)
  • They may predispose a cat to forming stones in the bladder and kidneys.
  • A male cat with cystitis is more likely to get a urinary obstruction if he also has crystals

Ash in the Diet

"Ash" is the component of food that is left over when the food is burned (i.e., it is the same as ashes).  It is composed of minerals, such as phosphorus and calcium. We used to try to limit ash in the diet because it may be associated with crystals. Ash is no longer considered a factor in causing cystitis.


Neutering predisposes cats to becoming obese and obesity predisposes cats to getting idiopathic cystitis. Other than that, there is probably no relationship between neutering and FIC.

Urinary Obstruction

There was a study that showed that some cats with cystitis have urethral obstruction and the study suggested that the obstructions were the cause of the cystitis. Most experts agree that this is almost never the case: the cystitis is the cause of the obstructions, not the other way around.

Signs of Cystitis

The signs seen in a cat with idiopathic cystitis are the same as the signs seen when a cat has a bladder infection.


Humans with cystitis describe it as being very painful and we are confident that the same is true in cats. Cats show pain in a number of ways including hiding, not eating, and vocalizing. Frequently the signs of pain are so subtle that humans don't know their cat is in pain.

Frequent Urination:

With cystitis, the nerve endings in the bladder are stimulated, making it feel to the cat as though they have to urinate, even when the bladder is empty. Humans will see the cat squatting as though to urinate with nothing coming out. This is problematic in that the exact same thing is seen when a cat has a urinary obstruction. They squat to urinate and no urine comes out.

House Soiling:

For reasons that are variable and not fully understood, some cats will urinate outside the litter box when they have cystitis.

Complications of Cystitis

Urinary Obstruction:

This is a common complication in male cats with idiopathic cystitis and very uncommon in female cats. It can be be due to either urethral spasms or material lodged in the urethra. When this happens the bladder fills with urine and becomes very painful. (Our experience is that cats react less when we handle a broken leg than they do when we touch an obstructed bladder). Eventually the pressure in the bladder builds to the point that the kidneys can no longer produce urine and permanent damage is done to the kidneys. When fully obstructed and not treated, the cat will be in extreme pain for 12 to 48 hours and then usually die. Very rarely the obstruction will resolve without treatment.

If your cat is squatting to urinate and no urine is coming out, you should consider it a life-threatening emergency. It cannot wait until morning.

Pain and Discomfort:

Cats with cystitis are always in pain, even though it may not be obvious to people.

It is important to realize that if your cat is going in and out of the litter box, trying to urinate frequently with little success, they are in pain.

Treatments for Idiopathic Cystitis

We don't know what causes idiopathic cystitis in cats and we don't really have any treatment that is proven to be particularly helpful. A big part of the problem is that cats who don't obstruct will usually get better within a week no matter what treatment is used. There are hundreds of treatments that people think work because they were tried and the cat got better.

We do, however, treat cats for idiopathic cystitis even though there aren't any good studies to support the effectiveness of any given treatment

Pain medication. We usually recommend a narcotic to alleviate pain for the sake of relieving pain. Since stress is a predisposing factor in idiopathic cystitis, it makes sense that treating for pain might shorten the course of the disease.

Alprazolam. This can help with anxiety and may help cats urinate more easily.

Fluids. We usually recommend that we give the cat subcutaneous fluids (fluids injected under the skin) and then that water be added to the cat's food. With cystitis, toxins from the urine are more able to leak into the bladder wall and it is felt that by giving the cat fluids, we can dilute out the toxins and make the urine less irritating to the bladder. By diluting the urine, we are also helping to dissolve any crystals and probably making it less likely that the cat will get an obstruction.

Antispasmodics.  We sometimes treat with drugs that can decrease urethral spasms. It is felt that this can help with some of the pain that cats experience.

Diet change. The majority of the cats that we see who have idiopathic cystitis are on dry food so we always discuss changing the patient to canned food. It is felt that the cat is less likely to form crystals and obstruct with canned food and the cystitis is less likely to recur if the cat is given canned food.

If a cat refuses canned food and is male, we will often use a dry prescription diet that is designed to decrease crystal formation. We don't do this because we think it will help with the cystitis but because we think that it will make them less likely to obstruct. These diets tend to be deficient in protein and other nutrients but can be useful for short term use.

There are a number of prescription foods (dry and canned) that are formulated for cats with idiopathic cystitis. They may be better than over-the-counter dry food for idiopathic cystitis but none have been shown to be superior to over-the-counter canned food for helping with this disease.

Amitriptyline. If a cat has idiopathic cystitis for more than a week or repeated episodes, we will sometimes try amitriptyline. This is a tricyclic "antidepressant" that has a number of effects that may help with idiopathic cystitis. We feel that it is helpful in a small number of cats.

Surgery. Surgical removal of the penis (perineal urethrostomy) is sometimes used in male cats with idiopathic cystitis to prevent obstruction. This surgery doesn't do anything to prevent cystitis but it can help prevent life-threatening obstruction. The surgery will predispose the cat to urinary tract infections later in life so we generally only perform it as last resort. We've done this surgery one time since opening in 2000.


Preventing Idiopathic Causes

To try to prevent idiopathic cystitis in cats we recommend:

  • Control the cat's weight.
  • Minimize stress (enrich the environment, etc.)
  • Change to a canned food and add water to the food.
  • Consider amitriptyline (see above) if recurrences are common.

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