Feline lower urinary tract disease (FLUTD) is a generic category term to describe any disorder affecting the bladder or urethra of cats.
It encompasses around 10 different diseases of the lower urinary tract, all of which can present with very similar symptoms:
frequent urination (polyuria) blood in urine (hematuria) painful, frequent urination of small volumes that are expelled slowly only by straining (stranguria) difficult or painful urination (dysuria) urinating in “inappropriate” places or house-soiling (periurea)
Some of these symptoms may be the result of a form of FLUTD which could result in a blockage of the male urethra (e.g. obstructive feline idiopathic cystitis). However the same symptoms can also present for a non-obstructive form of FLUTD. Therefore, a careful differential diagnosis needs to be undertaken to distinguish between an obstructive case (which is an emergency) and a non-obstructive case (which is not) given that the symptoms are very similar for both. The vast majority of FLUTD cases are non-obstructive, regardless of underlying cause.
FLUTD is common in adult cats, affecting from 0.5% to 1% of the population. It affects cats of both sexes. Males are more prone to problems related to obstructions due to their long, narrow urethra. Urinary tract disorders have a high rate of recurrence, and some cats seem to be more susceptible to urinary problems than others.
An older term, feline urologic syndrome (FUS) is obsolete. It was renamed to discourage the perception that the clinical signs seen represent one disease with one cause.
Causes
The most common cause of FLUTD in cats less than 10 years of age is non-obstructive feline idiopathic cystitis. Less common causes are urolithiasis, and urethral plugs which usually result when an attack of feline idiopathic cystitis is not self-limiting and escalates into a blockage of the bladder (i.e. obstructive FIC). Urinary tract infections (UTIs) can also be a cause of FLUTD but are very rarely seen in younger/middle-aged cats. However, in cats over the age of 10, UTIs are more frequently seen, particularly in female cats. The rarest forms of FLUTD for any age/sex cohort include anatomic defects, behavioural disorders and neoplasia.
There have been many risk factors identified for cats with FLUTD; however, it is likely that many factors (e.g., genetic, environmental, nutritional) play a role in this multifactorial disease.
Feline idiopathic cystitis
Feline idiopathic cystitis (FIC) is by far the most common form of FLUTD in young to middle-aged cats. It is a disease whose cause is not fully understood but is thought to be related to stress events and a cat's pre-disposition to anxiety, as well as certain lifestyle choices (e.g. a dry food diet, no access to outdoor space). Most cases of FIC (85%) are self-limiting and resolve themselves within 7 days, with or without treatment. A small minority of cases do not resolve themselves and can escalate into blockage of a male cat's urethra which is a life-threatening condition if not relieved (female cats, with a wider urethra, do not tend to block as a rule). GP-51, a specific glycosaminoglycan, lines healthy bladders of felines, where it prevents bacterial adherence and protects the bladder from the toxic properties of urine. Cats suffering from idiopathic cystitis, (i.e. unexplained inflammation of the bladder) excrete lower amounts of GP-51 along with other glycosaminoglycans, leaving the lining of the bladder exposed. Substances from the urine come into contact with sensory neurons in the bladder, causing pain and neurogenic bladder inflammation, producing the urge in the cat to strain and void frequently to minimise the intense discomfort resulting from this urinary contact. The sensory neurons are composed of unmyelinated C-fibers (group C nerve fiber), and when stimulated cause pelvic pain. Prolonged stimulation of the C-fibers causes chronic inflammation that is maintained through the release of the neurotransmitter substance P. This increases the vascular permeability of the bladder, allowing red blood cells and lymphocytes to enter.