FUS is a disease of the urinary bladder and urethra in cats. Female cats develop signs of cystitis (bladder infection). They will urinate frequently, often passing small amounts of bloody urine at the end of the stream. Cats with cystitis (bladder infection) often urinate outside the litterbox.

Male cats also show the same signs of cystitis, but males have a deadly component to their bladder infections. They may develop a total urethral obstruction preventing elimination of urine.

Urethral obstruction is caused by a mucus plug lodged in the urethra (the passage through which urine is eliminated from the body). The urethra in male cats is longer and narrower than in female cats, making obstruction more likely in males.

Total obstruction leads to retention of urine containing body wastes, imbalance of the electrolytes (potassium, sodium, etc.) of the body, and kidney damage. Loss of appetite, depression, and vomiting are common signs of urethral obstruction. If the mucus plug is not removed, coma follows and death results.

The specific cause of FUS is not well understood and is being extensively studied. The presence of mineral crystals in the urine and the acidity of the urine are also considered important factors. Struvite crystals are present in the mucus plugs that cause urethral obstruction. The crystals dissolve harmlessly in acidic urine but crystalize dangerously in alkaline urine.

Feline Urological Syndrome (FUS) is characterized by frequent urination, often outside of the litter box, and/or blood in the urine, and finally straining to urinate (staying in the box for long periods, often confused with constipation).

Diagnosis is made by palpating a baseball sized hard round bladder in the abdomen accompanied by cries of pain. Radiographs may be recommended to determine the presence of bladder stones. This “syndrome” is seen in all age cats, however, obese cats and cats fed high magnesium diets are at a greater risk. Male cats are at a higher risk to become obstructed, or blocked (unable to pass urine) due to crystals or stones in the urethra. Any cat that strains to urinate without actually passing urine, is depressed, starts vomiting, or appears to have a painful abdomen is considered a life threatening emergency. Seek veterinary care immediately.

Treatment of FUS includes antibiotic therapy and possible diet change. Surgery is necessary if bladder stones are present and catheterization is required if obstruction is present. Catheterization should be provided at least 3-4 days before being removed.