Cats have a tendency to suffer from bladder problems. Most of these problems need long-term management to prevent recurrence. It is very important to diagnose the cause of the problem accurately so that effective long-term management can be planned.

Irrespective of the cause of bladder problems, the symptoms tend to be the same: inflammation of the bladder leading to frequent urination; straining and pain during urination; and the urine may be cloudy or may contain blood. In male cats, blockage of the urethra can easily result in the over expansion of the bladder and even rupture of the bladder, with a buildup of toxins, which can lead to death within a few days.

Inflammation of the bladder has several causes. There are three main causes, though: struvite bladderstones; oxalate bladderstones; or interstitial cystitis. Other causes such as bacterial bladder infections and bladder tumours are occasionally found, but these are common only in old or immunosuppressed cats. Systemic diseases such as liver failure or other metabolic abnormalities can lead to crystal or stone formation in the bladder, but this is not common.

Bladderstones or crystals:

Crystals form in urine when the urine is over saturated with certain chemicals, which can no longer remain dissolved and therefore crystallize into solid particles. Aggregates of these particles will eventually form stones. Urine contains many different chemicals, and whether these crystals remain dissolved or crystallize depends on many factors. The excretion of crystal-forming substances by the kidneys is affected by the amount of these substances in the blood (and therefore in the animal as a whole) and the normal or abnormal function of the kidney.

The amount of water in the urine (or concentration) will affect these substances. This depends in turn on the amount of water the animal drinks, and the ability of the kidney to concentrate the urine.

The acidity (pH) of the urine is also very important, as certain chemicals can remain dissolved at a certain pH but if the pH changes they will crystallize.

Other interactions between chemicals and the temperature also play a role but since these tend to be consistent, are generally ignored. All these previously mentioned factors affect not only whether crystals form, but also the rate of formation and the structure of the crystals.

1. Struvite crystals: These are the most common crystals found in Hong Kong cats. They are formed by a mixture of magnesium, ammonia and phosphate. Unlike dogs, where these stones usually form during bladder infections, in cats these crystals tend to form continuously as the kidneys excrete excessive amounts of these three chemicals. Small stones, like grains of sand, form, which cause inflammation of the bladder. The pus and damaged bladder cells glue these crystals together into plugs, which easily block male cats urethras. A blocked bladder is always an emergency requiring surgery to unblock the bladder and hospitalization to treat the toxic effects. Prevention by strict diet is usually effective. Diets must be low in magnesium, phosphate and nitrogen (which forms ammonia), which mean lower protein levels, as protein is the main source of nitrogen. High water content, or diets that encourage drinking will also decrease the concentration of these chemicals. The pH of the urine is very important. A low pH (acidic) urine will prevent the formation of struvite crystals.

2. Calcium oxalate crystals: This is most common type of crystal in cats in the USA, but it is still fairly rare in Hong Kong. Small amounts of these crystals are found normally in cat’s urine, but large amounts may occur with high blood calcium or oxalate. However most cases of stone formation is in cats with normal blood calcium, and is caused by increased calcium and oxalate excretion, decreased citrate excretion (citrate prevents these crystals forming), acidic and concentrated urine. These factors are genetic and so this condition is more common in purebred cats. As long as no disease is present causing high blood calcium, prevention of these crystals is by diet. Canned diets are essential. They must be low in oxalate and calcium, high in citrate, low in protein and sodium and not make the urine too acidic. Diets, however, cannot completely stop these crystals forming, as the underlying cause is often genetic, but they can reduce the frequency of bladder problems.

3. Interstitial Cystitis: This is the common name for inflammation of the bladder of unknown cause. Inflammation of the bladder occurs without crystals, bacteria or any other known causes being present. Pus and blood are present in the urine, and urination is painful and frequent. While symptoms may be severe, they usually resolve within a few days. Mild cases may recur only a few times a year, but some cases, inflammation may be almost permanent. Stress is believed to play a role, and some researchers believe viruses, such a herpes virus, or abnormal forms of bacteria not visible under the microscope, may be involved. We do know that in most cases, cats respond to certain drugs usually used for behavioural problems (antidepressants). These may decrease stress, as well as relax the bladder muscle and reduce inflammation symptomatically in the bladder. Although these drugs control this form of bladder inflammation effectively, until the cause is found, no cure will be available. It has been noticed that diets to prevent urine crystals also decrease the frequency and severity of the symptoms, so these cats also need to be on a strict diet.

Almost all bladder problems in cats are long-term or recurring, so long term management is essential. Correct diagnosis is necessary to find the correct diet, and where necessary, medical and surgical treatment.