Feline lower urinary tract disease (FLUTD)
Feline lower urinary tract disease (FLUTD; feline urologic syndrome, feline interstitial cystitis) is a common urinary disease of cats which presents as haematuria, dysuria (abnormal urination), stranguria (pain during urination). In male cats, this commonly leads to urethral obstruction.
In cats, the leading causes are chronic inflammation and urolithiasis. The correlation between diet and FLUTD suggests that domestication and being fed commercial dry food contributes to the rising morbidity of this disease in cats worldwide.
FLUTD is a syndrome which excludes other causes of urinary tract disease such as trauma, neoplasia of the urinary tract or incontinence (which has a psychoneurological origin, particularly in older cats or cats suffering spinal injury).
FLUTD affects the entire lower urinary tract, including bladder, urethra and genitals. In the majority of cases (>80%), bacteria are not involved, or play only a minor part in the pathogenesis of the disease. The only exception to this rule appears to be in cats aged >10 years, where bacterial cystitis is more common.
- Interstitial cystitis (IC) - this is the most common type of FLUTD. Humans with IC appear to suffer from a range of co-morbid conditions, and there is some data to suggest this may be the case in cats. For example, FLUTD has been reported to be a co-morbid condition in cats with separation anxiety syndrome, hypertrophic cardiomyopathy and obesity.
- Uroliths - only about 25% of cats with FLUTD have uroliths. Dry foods will aggravate any underlying bladder infection/inflammation. This is because of the higher mineral content (ash) and lower water content of dry foods. In a recent survey, the percentage of struvite uroliths in cats has declined, compared to calcium oxalate uroliths. Struvite and calcium oxalate uroliths were common in Domestic shorthair, Himalayan, Persian, and Siamese cats. Urate uroliths appear to be more common in Egyptian mau. Other uroliths in cats include purine, xanthine, oxalate and cystine.
- Urethral plugs (matrix) - typically around 20% of cases. A urethral plug is composed of a matrix (mucoprotein‐inflammatory debris and mucous) and minerals (struvite predominates). These are generally found at the penile tip.
- Pseudomembranous cystitis - inflammatory cystitis, presents as acute obstruction and renal failure
- Viral - many cats with cystitis have concurrent FHV (herpes virus) infection
- Cystitis, bacterial - caused by Staphylococcus spps, Streptococcus spp, Citrobacter spp, Acinetobacter spp, E. coli and Enterococcus spp. A predisposition in Norwegian forest cats has been reported.
- Fungal infections - primarily opportunistic Candida spp
- Chronic renal disease with secondary haematuria/cystitis
- Ectopic ureter
- Neoplasia of the urinary tract - usually transitional cell carcinoma. Rare in cats compared with dogs, presumably due to a difference in tryptophan metabolism that results in low urinary concentrations of carcinogenic tryptophan metabolites. The mean age of affected cats is 9 yr, often affecting purebred cats such as Siamese.
- Emphysematous cystitis associated with diabetes mellitus
- Nematodes, rarely, such as Pearsonema spp and Rhabditis strongyloides.
Haematuria (blood in urine), pollakiuria (frequent urination), and stranguria (painful urination) are the characteristic clinical signs of FLUTD in cats. Urolithiasis is usually suspected based on clinical signs of haematuria, dysuria, or urethral obstruction. Urinalysis, urine culture, radiography, and ultrasonography may be required to differentiate uroliths from urinary tract infection or neoplasia. Radiography, cystoscopy, or ultrasonography are critically important to detect uroliths because only ~10% of feline urocystoliths can be detected by abdominal palpation. Uroliths with a diameter >3 mm are usually radiodense; however, because smaller uroliths are common, double contrast radiography may be required for detection. Radiographic evidence of uroliths is seen in ~20% of cats with haematuria or dysuria. The usual clinical approach to grossly observable urocystoliths is surgical removal or lithotripsy where available, followed by dietary therapy instituted as a preventive measure. For sterile struvite uroliths, medical dissolution is the preferred treatment.
Some cats, especially male cats, can have crystals in the urine which will completely block the urethra (the tube from the bladder to the genitals). In these cases, the bladder cannot empty. Overfilling of the bladder occurs and unless the bladder is catheterised, will burst. These cases are considered emergencies by veterinarians. If the obstruction is not relieved within 48 hours, most cats will die from kidney failure and the retention of toxins that were not removed by the kidneys. Because the urethra is relatively larger in the female cat, the emergency posed by complete obstruction is almost always found in male cats.
1. Combine history including behavioural history, physical examination, laboratory data, radiographs +/- abdominal ultrasonography
2. Complete urinalysis (USG, dipstick, sediment exam, and ideally C+S) should always be performed: haematuria, pyuria, proteinuria is often found. Other finding include crystals, mucoproteinaceous debris, pH imbalance, bacteria, neoplastic cells and inflammatory cells. NB: crystals dissolve in the urine within 4-6 hrs - therefore do in-house sediment exam ASAP to identify crystals
3. Minimum electrolytes and biochemistry blood profile data base required, although TP/PCV, biochemistry and electrolytes/blood gasses may be run. Azotaemia, hyperphosphataemia and acidosis may be noted in more severe cases.
4. Diagnosing this disease can be difficult. Other clinical tests such as bladder imaging can help.
In acute medical cases of urethral blockage and bladder overfilling, feline patients should have ECG monitoring before and during anaesthesia for catheterisation. Cardiac disturbances can be seen with K+ above 6.5-7.0 mmol/L; and these may include bradycardia, atrial standstill, spiked T-waves, accelerated idioventricular rhythm, ventricular tachycardia, or fibrillation. Therapy for hyperkalemia should be instigated.
Relief of obstruction should be attempted without GA in extremely depressed cats. If restraint is required, use low dose diazepam/ketamine (1-2 mg/kg IV) or propofol IV. Otherwise, general anaesthesia is induced (with either propofol, diazepam/ketamine, or alfaxolone) and maintained with isoflurane and oxygen.
Male cats who frequently suffer from cystitis and blockage of the urethra have a high risk of kidney damage and sudden death due to bladder rupture.
In these cases, the cause is usually the presence of large quantities of urinary crystals in the bladder. Surgical intervention usually involves either a cystotomy or perineal urethrostomy. In cases where an anesthetized male cat cannot be catheterized, an emergency cystotomy and bladder marsupialization is recommended as a life-saving procedure prior to perineal urethrostomy.
With a perineal urethrostomy, (often called a 'sex change operation'), the penis is amputated and the urethra exteriorised as a makeshift vagina-like opening, thus preventing any further blockage of urine. Long-term complications are relatively minor when performed by an experienced surgeon. In some cases, urethral blockage at the peliv urethra may require a pre-pubic urethrostomy.
Monitor for post-renal azotaemia due to tubular back-pressure causing a reduction in the GFR. Monitor also for post-obstructive diuresis then maintain fluid balance in light of post-obstructive diuresis (normal urine output is 1-2ml/kg/hr). Consider using phenoxybenzamine or prazosin as an alpha-1 antagonist to relax the internal urethral sphincter. Consider starting as soon as the urinary catheter is in place. Acetylpromazine also has alpha-1 antagonist activity, so can be used to sedate and help express bladders if there is some functional obstruction post-catheter removal. The use of pentosan polysulphate to minimise clinical signs is at present debatable.
In cases of low-grade chronic FLUTD, a dietary change is strongly recommended, using a prescription diet. Routine analgesia is preferred, using NSAIDs (e.g. meloxicam) as a primary choice of drug. Use of urinary acidifiers may help alleviate clinical signs of dysuria.
The presence of crystals suggests that a diet change is in order, including adding urinary acidifiers such as Acidurin® to help keep the urine acidic and prevent further crystals from forming. It is also important to feed the cat dry food that is low in minerals and which produces and acidic urine (such as Hills C/D diet®) or else avoid dry foods altogether and feed only fresh food or tinned food, which have a higher moisture content. Because cats that get cystitis normally have recurring problems, it is important to keep them on a modified diet, urinary acidifying tablets and reduced stress.
One aspect of long-term management of FLUTD is to promote increased water consumption by the cat. This can be problematic as cats are reluctant drinkers. Increased drinking has been thought to increase the mechanical flushing of the urinary bladder and thus reduce the formation of crystals. One method of stimulating water intake in cats is by increasing the salt content of the food. Canned food are a frequent recommendation as they contain 70-80% water. Several studies have shown that increasing dietary salt (NaCl) can increase water intake and urine volume, and decrease urine specific gravity. It has been suggested that increased salt intake in cats with existing FLUTD may aggravate underlying kidney disease and elevate blood pressure, but a comprehensive study by Xu et al showed that changes in dietary salt intake had minimal effects on total body hydration status, blood pressure and markers of renal function. Rather than a risk factor, they also noted that increasing salt in diet had a protective influence against the development of chronic renal disease in cats.
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