Lower urinary tract diseases of cats are a common, and sometimes frustrating, group of clinical problems that practitioners must deal with.
Lower urinary tract diseases of cats are a common, and sometimes frustrating, group of clinical problems that practitioners must deal with. Any disorder of the lower urinary tract may cause signs of lower urinary tract disease, the key is to understand the diseases that occur in cats and how they differ from the classic UTI/stone based diseases of dogs. In cats under 10 years of age, idiopathic cystitis (previously termed interstitial cystitis) is by far the most common cause of clinical disease, while in cats over 10 years of age, urinary tract infections are more common. The focus of this review is on the control, prevention and, where possible, treatment, of lower urinary tract disease in cats.
Feline lower urinary tract disease is condition characterized by painful, difficult or inappropriate urination (urinating outside the box), hematuria, and possibly the formation of stones in the urinary tract. The key is to recognize that there are many potential causes for the above symptoms: including crystalluria/urolithiasis, urinary tract infection or idiopathic. As many as 65% of cats under 10 years of age with lower urinary tract signs suffer from the idiopathic form of the disease – currently termed idiopathic cystitis – where there are no crystals, no UTI, no stones and no identifiable cause or if there are crystals or infection they are occurring secondary to interstitial cystitis as the primary cause. The classic progression of this disease is for the clinical signs to last 3-7 days with self resolution during that time (the reason why many have believed mistakenly that the signs resolved due to antibiotic or anti-inflammatory therapy). For these cats, no drug therapy to date has shown consistent benefit, and some drugs prescribed long term may have detrimental effects. However, in a controlled study, dietary therapy using a canned cat food diet designed to maintain a dilute urine and urine pH in the neutral range significantly reduced the rate of recurrence (90% did not recur over a 12 month trial period, compared to 60% of the control group). While there is still much to be learned about cats with idiopathic cystitis, increasing water intake and urine dilution appears to be very beneficial in the therapy of these cats.
Because the disease is associated with pain and mucosal hemorrhage due to defects in the bladder GAG layer – management is aimed at control of pain and prevention of complications of hemorrhage (blood clots forming concretions that cause an obstruction or nidus for crystal matrix formation). The inflammation associated with idiopathic cystitis in the bladder wall is not mediated by COX – mechanisms, thus, steroids or non-steroidal therapy will not result in significant control of discomfort. The most effective drug therapy for pain control in these cats appears to be opioids (buprenorphine or butorphanol). The best way to prevent clot formation or crystal nidus formation is to keep the urine as dilute as possible – thus, canned food, increasing water intake by other means, or giving SQ fluids are important aspects of therapy.
Finally cats with this disease, similar to humans with interstitial cystitis, appear to have co-morbid conditions as part of their disease: obesity, separation anxiety (and other stress responses) and hypertrophic cardiomyopathy. Research indicates that cats with idiopathic cystitis have an enhanced activation of the stress response system (sympathetic) from higher brain centers. Although more work is needed to fully understand this disease, therapy of idiopathic cystitis in cats should also be focused on methods of decreasing sympathetic responses. There is a website (www.indoorcat.org) that is dedicated to helping cat owners better understand this disease and indoor cat health.
Development of urocystoliths in cats is a well known, and reasonably well-understood, phenomenon resulting from loss of solubilization of ions (primary Mg, NH4, PO4) or other minerals/substances found in urine (oxalate, urate, silica, cystine) in urine. The process is complex and requires a combination of preceding events to provide the appropriate environment for the formation of crystals and ultimately urinary stones.
There are a variety of types of urinary stones. Some types of stones are readily amenable to dietary dissolution and prevention, while others are not, so one of the most important steps in management of urolithiasis is to know what type of stone is present. In addition, it is important to recognize that while the presence of crystals in the urine may allude to a particular stone type (but doesn't prove the type or that stones are present), not all uroliths are of a single type –which will greatly complicate their management. Thus, surgical removal and stone analysis can be a very important component of diagnosis.
In the early 80's the primary type of urinary stone found in cats was composed of magnesium, ammonium and phosphate (in 1985, the number was 80% of all stones). However, in 1995, only 35% of the stones were struvite, and 54% of the stones submitted to the University of Minnesota Urolith Center were calcium oxalate. The primary reason for this decrease in struvite stones in cats was due to dietary manipulation of feline foods (low magnesium, low phosphorus, and adding urinary acidifiers to the diets). Further, because young cats rarely develop bacterial UTI, this aspect of struvite formation is not a consideration as it is for dogs. However, the result of producing low magnesium, low phosphorus, acidified diets has resulted in a shift in stone type that creates an incredibly bigger challenge: as calcium oxalate stones are much more difficult to manage.
1. Dietary dissolution of these stones can be achieved with short term use of a diet that is: 1) extremely low protein, magnesium, ammonium, phosphate, and 2) is highly acidified to lower urinary pH to less than 6.0. Because these diets are highly protein restricted (16% protein on a dry matter basis)– they should not be fed for long periods (4-6 months) or as a maintenance diet and should be discontinued if the stones are not dissolved in a 1-2 month period. Hill's Prescription Diet s/d is the primary diet available for dissolution of struvite uroliths, however, struvite stones will dissolve in any cat fed a diet that reduces the concentration of the substrate, decreases the urine pH, and increases the urine volume.
2. Prevention of struvite uroliths often times can be successfully achieved by using acidified diets formulated with lower levels of protein, magnesium, and phosphate (but not as restrictive as a dissolution diet). In addition, prevention or early correction of recurrent urinary tract infections is essential for the long term management of this type of stone disease.
3. There are a variety of diets commercially formulated for prevention and control of struvite uroliths. They include: Hill's Prescription diet c/d, RC/Waltham S/O, and RC/Innovative Veterinary Diets (IVD) Control. Eukanuba Senior Plus is recommended as an appropriate diet for dogs to prevent formation of struvite stones.
The most common urinary stone type presently reported in cats is calcium oxalate. These stones are more difficult to manage via dietary or medical therapy. However, because they may be caused by identifiable medical or drug therapy – this is one of the most important aspects of therapy of these stones. Any disease process, diet, or drug that increases the excretion of calcium can lead to the development of calcium containing (oxalate, phosphate, apatite) stones. Thus, identification and correction of those causes, if possible, are extremely important in the management of these uroliths.
1. Westropp JL, Buffington CAT. Etiopathogenesis of feline idiopathic cystitis. In: August JR, Consultations in Feline Internal Medicine. Elsevier, Philadelphia, p. 435, 2006.
2. Bartges JW, Kirk CA. Nutrition and lower urinary tract disease. Veterinary Clinics of North Am, 36: 1361, 2006.