Management of urethral obstruction in cats (Proceedings)
Lower urinary tract disease in cats was described as early as 1925. Over the years, the terms "feline urologic syndrome" (FUS) and "feline lower urinary tract disease" (FLUTD) have been used to describe the group of clinical signs related to problems voiding. However, these descriptive terms do not identify the underlying etiology. The clinical signs of FLUTD are not specific, and may include:
It is helpful to divide cats with FLUTD into obstructive and non-obstructive uropathy for treatment purposes. Obstructive uropathy is most commonly seen in male cats due to the small diameter of the male urethra. Typical clinical signs include dysuria, hematuria, frequent attempts to urinate, and licking at the penis or prepuce. Some cats will also have signs of systemic illness, such as lethargy and anorexia. Cats suffering from prolonged obstruction may present moribund.
Urethral plugs and urethroliths have been identified as the most common causes of obstruction in male cats1-2. Other potential causes include urethrospasm, trauma, congenital defects, stricture and neoplasia. Since 1980, the frequency of urethral obstructions in cats has been declining, paralleling a similar decline in the frequency of urethral plugs and urethroliths3.It is currently not known what causes urethral plugs to form. Many urethral plugs are composed of struvite crystals in a proteinaceous matrix. One theory suggests that urethral plugs form in cats with underlying idiopathic cystitis. Plasma proteins enter urine from suburothelial vascular leakage and may trap crystals in the lumen of the urethra, resulting in obstruction. Oozing of plasma proteins into urine combined with active inflammation may increase the urine pH, thus contributing to the precipitation of struvite crystals. Although calcium oxalate uroliths are now at least as common as struvite uroliths, the mineral composition of urethral plugs continues to be predominantly struvite4. Other urethral plugs are composed almost totally of matrix (mucoproteins, albumin, globulins, cells, debris) or sloughed tissue and blood.
Uroliths are organized concretions containing primarily crystalloids with a small amount of organic matrix. The most common components of uroliths are struvite and calcium oxalate4-6 , but recently uroliths composed of dried solidified blood have been reported7. Urine is commonly supersaturated with crystalloids, so crystalluria itself is not a disease and does not need to be treated unless it is associated with clinical signs of FLUTD. Struvite uroliths most commonly occur in the bladder and usually form in sterile urine in the cat. Cats with struvite uroliths are generally younger than cats with calcium oxalate uroliths. Other risk factors include an indoor sedentary lifestyle, obesity, low water intake and alkaline urine. The Himalayan and Persians breeds appear to be predisposed to both types of uroliths.6
Calcium oxalate uroliths have been increasing in frequency in cats since the 1980s as diet manufacturers changed ingredients to promote more acidic urine. By 1993, calcium oxalate uroliths were diagnosed with approximately the same frequency as struvite uroliths, and the prevalence increased in subsequent years. The prevalence of struvite uroliths may have increased from about 2000 to 2004, and then started to decline.6
Calcium oxalate uroliths may be found in the bladder, urethra or kidney and are not usually associated with infection. Cats with calcium oxalate uroliths are generally older and neutered males. Other risk factors include an indoor sedentary lifestyle, obesity, low water intake and feeding acidifying diets. Persian and Himalayan cats appear to be predisposed to this type of urolith as well. Altered calcium metabolism may play a role in calcium oxalate urolithiasis in some cats, so affected cats should be evaluated for hypercalcemia.
Cat with urethral obstruction should be treated as emergencies when presented.8 In particular, cats that have been obstructed 48 hours or more may be severely ill and require crisis management. A thorough assessment of the cat's condition should be made before attempting to relieve the obstruction.