Feline idiopathic cystitis

What it is

Feline idiopathic cystitis (FIC) is a diagnosis of exclusion: the cat shows signs of lower urinary tract disease (so-called FLUTD, feline lower urinary tract disease) with no uroliths, infection, neoplasia or other demonstrable cause. It is the most common cause of these signs in cats under about 10 years of age; bacterial urinary tract infection, by contrast, is uncommon in young cats and more typical of older cats with chronic kidney disease, diabetes or hyperthyroidism.

It is now considered a systemic syndrome rather than a disease of the bladder alone, with similarities to human interstitial cystitis (bladder pain syndrome). Affected cats show an altered stress response, with sympathetic nervous system activation without a proportionate adrenal response, a defective urothelium with a thinner glycosaminoglycan layer and increased permeability, and neurogenic inflammation: sensory fibres in the bladder release neuropeptides that cause oedema, submucosal haemorrhage and pain. Other problems (digestive, skin, behavioural) often coexist.

Who it affects

Cats of roughly 2 to 10 years, kept indoors, overweight, inactive, eating mainly dry food and drinking little, and living in stressful environments (conflict with other cats, changes in the household, dirty or too few litter boxes). Males and females are affected equally, but in males FIC can be complicated by urethral obstruction.

Anatomy involved

• Urinary bladder: thickened wall and oedematous mucosa, petechial submucosal haemorrhages (glomerulations on cystoscopy) and loss of the protective glycosaminoglycan layer.
• Urethra: in the male it is long and narrow, especially the penile part; urethral plugs of protein matrix and crystals, or urethral spasm, can obstruct it.

Clinical signs

Pollakiuria (frequent, small voidings), stranguria, dysuria, haematuria, urinating outside the litter box (periuria) and licking of the genital area. Episodes usually resolve on their own within a few days to a week, but they frequently recur, often after stressful events. A male cat straining without passing urine may be obstructed and is an emergency.

Diagnosis

It is made by excluding other causes:

• Complete urinalysis (haematuria and proteinuria without bacteria in many cases; struvite crystalluria may be present and does not on its own indicate disease) and urine culture by cystocentesis.
• Imaging: abdominal radiographs including the whole urethra and ultrasound to rule out uroliths, plugs, polyps or neoplasia; the bladder wall may appear thickened.
• In recurrent cases, contrast cystourethrography or cystoscopy.
• The bladder must always be palpated in a male cat with stranguria to rule out obstruction.

Treatment

In the acute episode, analgesia (opioids such as buprenorphine; non-steroidal anti-inflammatories only in well-hydrated cats with normal kidney function) and stress reduction. Antibiotics are not indicated without proven infection. Prevention of recurrence relies on multimodal environmental modification (MEMO): enough clean litter boxes in quiet places, separate resources in multi-cat households, scratching posts, elevated areas, play and predictable routines; and on increasing water intake, with wet food or water fountains. Therapeutic urinary diets and synthetic feline facial pheromones have been used, with variable evidence. Amitriptyline has been used in severe, refractory cases. The prognosis for each episode is good, but many cats relapse.

Key studies

• iCatCare consensus (Taylor et al., 2025): the current reference guideline for diagnosing and treating idiopathic cystitis and the other feline lower urinary tract diseases.
• Systematic review of the management of recurrent idiopathic cystitis (Macleod et al., 2025), covering 22 studies. Only two measures are supported: multimodal environmental modification (MEMO) and therapeutic urinary diets, wet ones in particular. The authors found no evidence for non-steroidal anti-inflammatory drugs, glycosaminoglycans, prazosin, short-term amitriptyline or intravesical lidocaine. They warn that primary studies are few and of low quality.
• Kruger et al. (2015), a randomised, masked trial of 31 cats fed a therapeutic diet or a control diet. The therapeutic diet led to fewer episodes with several clinical signs (0.7 versus 5.4 per 1000 cat-days). The proportion of cats with any recurrence did not differ (4 of 11 versus 9 of 14). It is a small, industry-funded trial.