Signs, causes, prognosis and treatments for FLUTD

FLUTD is subdivided into obstructive and non‑obstructive disease. Cats with obstructive disease are unable to pass urine, often referred to as “blocked” cats (Figure 1).

Urethral obstruction is a veterinary emergency – cats with this condition may die within two to three days if not treated.

Cats with non-obstructive disease are able to pass urine and typically strain to pass small amounts of urine on a very frequent basis. The urine may appear abnormal (for example, bloody), the cat may show signs of pain when straining and periuria may be present due to the cat’s urgency to urinate. Causes are summarised in Table 1.

How is FLUTD diagnosed?

Diagnosing the cause of FLUTD is especially important in cats that show repeated episodes or where the clinical signs are persistent.

Diagnosis may require a full behavioural and clinical history, physical examination, blood and urinalysis, imaging (including contrast radiography) and possibly biopsy.

Clinical history taking

Typical clinical signs of FLUTD include dysuria, haematuria, pollakiuria and periuria. Acute episodes of FLUTD can be very distressing for cat and carer.

Feline idiopathic cystitis (FIC), the most common cause of FLUTD in cats, is currently considered to be an “anxiopathy” – a disorder related to chronic activation of the central threat response system (CTRS). It is thought this may develop as a result of genetic, familial and developmental factors.

For example, a traumatic experience to the queen when the kitten is in utero may sensitise the CTRS, leaving the newborn kitten susceptible to problems in the future.

A susceptible cat is one with a chronic perception of threat impacting on its nervous, endocrine and immune systems, with the end result of clinical signs related to a number of organ systems including the bladder and lower urinary tract (Westropp et al, 2019).

The clinical signs of FLUTD are interpreted to be the bladder’s response to stress in these cats. Stress, therefore, plays an important role in triggering and/or exacerbating signs of FIC.

Chronic and inescapable stresses are thought to be most important. Characteristics of a cat with FIC often include a cat that is asymptomatic when in a “stress-free” environment, but which suffers from relapses of clinical signs when stressed.

Obese cats and those with a less active lifestyle are often over-represented. The history in these cases may therefore reveal:

• Evidence of chronicity, waxing and waning of clinical signs in response to stressful events.
• A history of familial involvement may exist – for example, litter mates suffering similar problems.
• Involvement of other organ systems resulting in clinical signs such as vomiting, diarrhoea, poor appetite, altered social interactions, lethargy, altered grooming and enhanced pain‑like behaviour at the same time as the urinary signs.

A behavioural history is important to look for evidence of tension with other cats in the household/neighbourhood and other causes of stress in the home that may be exacerbating clinical signs. If identified, these represent a key target for intervention.

Physical examination

Of key importance in the cat with FLUTD is establishing whether the urinary bladder is empty or full.

A cat with urethral obstruction and a full bladder needs emergency treatment.

Many cats with FLUTD will have an empty, possibly painful bladder on palpation and the remainder of the clinical examination may be unrewarding.

Laboratory tests

In non-obstructed cats with signs of FLUTD, blood profiles are often unrewarding, but these are important to include in any obstructed cats where dehydration, electrolyte and acid-base disturbances are common.

In older cats, signs of FLUTD may be associated with illnesses such as diabetes mellitus, hyperthyroidism and chronic kidney disease, so routine blood profiles are helpful in making an accurate diagnosis.

Urinalysis is a key component of investigations in all cats with FLUTD. Urine should be observed, and its colour, clarity and presence of gross contamination determined.

The urine specific gravity (USG) should be assessed using a refractometer. Urine may be defined as isosthenuric (USG = 1.007-1.015, same as glomerular filtrate), hyposthenuric (USG lower than 1.007) or hypersthenuric (USG higher than 1.015). A 5ml urine sample can be centrifuged, and the sediment stained and examined by light microscopy. Normal findings are summarised in Table 2.

Of prime importance for chronic/repeat cases are:

• Assessment of USG using a refractometer: Most cats with FIC will produce very concentrated urine with a high USG (for example, higher than 1.050). Cats with concurrent diseases – such as chronic kidney disease, hyperthyroidism and diabetes mellitus – will typically have a reduced USG (lower than 1.035)
• Utility of the dipstick: it is important to remember that dipsticks are unreliable for a number of parameters. For example, healthy cat urine commonly produces a reaction on the leucocyte pad, so a positive leucocyte reaction should not be taken as diagnostic for a bacterial urinary tract infection (UTI). Dipsticks are helpful in identifying presence of glucose and ketones consistent with a diagnosis of diabetes mellitus, bilirubin in jaundiced cats and blood in microscopically haematuric cats.
• Sediment examination: more helpful than a dipstick in identifying signs of a bacterial UTI, sediment examination can also help identify crystals and casts (Table 2).
• Bacterial culture: while bacterial UTIs are not the most common cause of FLUTD, it is important to rule this out as a potential cause.

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  Monitoring litter boxes for occult haematuria: this can be helpful in detecting recurrence of problems at an earlier stage than otherwise might be possible (Figure 2).

Imaging

Imaging via radiography and ultrasonography is recommended for cats suffering from repeated/persistent clinical signs.

FIC is a diagnosis of elimination – the role of imaging is to rule out other causes of the clinical signs, such as urolithiasis and neoplasia (Table 1). Positive contrast urethrography can be helpful in identifying urethral disease.

Advanced imaging, such as CT, is now being performed more frequently in cats with FLUTD, and excretory urography CT is now a recommended technique for ectopic ureter investigation.

Biopsy

In a small number of cases, a biopsy of the bladder or other associated lower urinary tract tissues may be indicated to confirm a diagnosis.

Management of cats with FLUTD

Management of FLUTD depends on the diagnosis made.

Almost all causes of FLUTD benefit from measures that increase water intake (Table 3). Success of these strategies can be measured through USG assessment (ideal is a USG lower than 1.035) and/or monitoring size of urine clumps if a clumping cat litter is used (Figure 3).

Providing an “optimal” toileting facility and adequate key resources for all social groups within the household is also vital.

Cats with FLUTD should have access to a litter box. This should be:

• Generous in size – it should be at least 1.5 times the length of the cat’s body from nose to tail base.
• Easy for the cat to get in and out of – for elderly cats with OA, having a low-sided access point can be an advantage.
• Contain a fine, sandy consistency clumping cat litter – this is most comfortable for the cat to stand on and is most inviting as a substrate. Faeces and clumps of urine should be removed at least twice a day, and the entire tray emptied, cleaned and refilled at least once a week (Figure 3).
• Perfumed litters, litter tray liners and covered litter trays should be avoided – these are all orientated towards the owner, not the cat.
• Ensure an adequate number of litter boxes are in the household. As a general rule, one litter tray should be present for each cat, plus one extra – and these should be in different locations so no opportunity exists for one cat to prevent access to the litter box by another.
• In some situations it can be helpful to “view” urination – for example, via a webcam – in cats with dysuria and/or urethral obstruction (Figure 4).

Dietary management is often a pivotal component of management in cats with FLUTD.

Specially designed urinary diets are effective in struvite urolith dissolution, reduction of crystalluria (relevant in cats susceptible to urethral plugs), and struvite and oxalate urolith prevention. Several maintenance urinary diets have now shown to be effective in struvite dissolution, meaning that a strict dissolution diet, which is typically very acidifying, is not needed.

For example, a Hill’s study indicated that while a dissolution diet (Hill’s s/d) took on average 13 days to result in stone dissolution, its maintenance urinary diet (Hill’s c/d) took a mean of 27 days (Lulich et al, 2013).

A more recent study involving a different maintenance urinary diet (Purina St/Ox) for cats with urolithiasis resulted in dissolution of struvite stones within two weeks (Torres‑Henderson et al, 2017).

Advantages of feeding a maintenance urinary diet include owner reassurance that the food is also safe for other cats in the household to eat. Unlike the situation in dogs, most struvite uroliths in cats are sterile and, therefore, antibiotic therapy is not usually required. Nonetheless, bacterial urinary culture is recommended in all patients with struvite stones, where possible, and is especially important in older cats where bacterial UTIs are more common.

General strategies useful in stone prevention include encouraging water intake with the aim of reducing relative supersaturation (RSS), a measure of the risk of crystallisation. Specially designed “urinary diets” are typically RSS tested with a formula that reduces the risk of stone and crystal formation.

In general, fluid intake is higher when a moist diet is fed, reducing the risk of stone formation, so this approach is preferred where possible. Additional dietary vitamin B₆, glycosaminoglycans and long‑chain polyunsaturated fatty acids – commonly included in therapeutic urinary diets – are also thought to assist in reducing oxalate and struvite stone formation (Hall et al, 2017).

Successful long-term treatment of cats that have suffered from urethral plugs involves use of nutritional strategies aimed at reducing the number of crystals in the urine. Although it is normal for cats to produce crystals in their urine, especially if they are fed a standard dry diet, reduction of crystal numbers can help to reduce the formation of plugs. Specially formulated therapeutics diets, such as maintenance diets, designed for cats with FLUTD are recommended.

Dietary management is also of benefit in some cats with idiopathic cystitis. For example, feeding both dry or wet formulations of Hill’s Prescription Diet c/d Multicare Feline reduced the rate of recurrent episodes of FIC signs by 89 per cent in one study (Kruger et al, 2015).

Adding “stress‑alleviating” compounds – such as alpha‑casozepine and L-tryptophan – to therapeutic urinary diets has been reported to benefit some cats with FIC (Meyer and Bečvářová, 2016; Naarden and Corbee, 2020).

One study involving 31 cats with acute non‑obstructive FIC reported that feeding a therapeutic urinary stress diet (Hill’s c/d stress) was associated with a significantly lower recurrence rate compared to cats fed a variety of commercial diets. Again, in this study no significant difference existed between cats receiving wet versus dry formulations of food, although the numbers of cats involved was low (Naarden and Corbee, 2020).

Some dry formulations of therapeutic urinary diets contain increased salt (sodium chloride) levels which have been shown to encourage thirst and production of more dilute urine (Hawthorne and Markwell, 2004), therefore potentially benefiting many cats with FLUTD – especially those resistant to transitioning to a wet food.

Summary

FLUTD is commonly encountered in clinical practice. The best outcome is associated with an accurate diagnosis and appropriate management.

Generally helpful strategies in cats with FLUTD include tactics that encourage increased water intake and reduce stress in the home.

Providing an optimal litter box is important and where possible, monitoring urination can be useful in detecting recurrence at an earlier stage.

Dietary management is often helpful in management of cats with FLUTD, including cats with urolithiasis, urethral plugs and idiopathic cystitis.