Etiology

2. Etiology

Worldwide, idiopathic cystitis is by far the most common cause of FLUTD reported in male and female cats (Kruger et al, 1991; Buffington et al, 1997; Osborne et al, 2000; Lekcharoensuk et al; 2001a; Gerber et al, 2005) (Figure 1, Figure 2, Figure 3).

Figure 1. Conditions responsible for the clinical signs of lower urinary tract disease in european cats. (Adapted from Gerber et al, 2005).

Figure 2. Conditions responsible for the clinical signs of lower urinary tract disease in european cats. (Adapted from Gerber et al, 2005).

Figure 3. Frequency of disorders in male and female cats in the united states with signs of FLUTD. (Adapted from Osborne et al, 2000).

Urolithiasis is the second leading cause of FLUTD. Uroliths can form anywhere in the urinary tract but the vast majority in cats occur in the bladder (Cannon et al, 2007). The majority of uroliths in the bladder are composed of magnesium ammonium phosphate (struvite) or calcium oxalate. Conversely, nephroliths are typically composed of calcium oxalate (Lulich et al, 1994).

The prevalence of struvite and calcium oxalate uroliths in cats has changed over the last 20 years (Table 1). Struvite uroliths analyzed at two laboratories in the USA performing quantitative analysis far outnumbered calcium oxalate uroliths before the late 1980s (Cannon et al, 2007). Between 1984 and 1995, the proportion of calcium oxalate uroliths submitted to the University of Minnesota Urolith Center increased from 2% to 40% (Osborne et al, 1996b). By the mid 1990’s, struvite urolith submissions began to decline and calcium oxalate became the number one submission in North America and other parts of the world (Lekcharoensuk et al, 2001a; Cannon et al, 2007; Forrester, 2006; Houston et al, 2003; 2006; Gerber et al, 2005). However, since 2002, struvite uroliths have been on the rise and have surpassed calcium oxalate as the number one urolith submission in the USA (Figure 4). Based on 9221 feline uroliths analyzed at the Minnesota Urolith Center in 2005, the most common mineral types were struvite (48%), calcium oxalate (41%) and purine (4.6%) (Forrester et al, 2006). In Canada, equal numbers of struvite and calcium oxalate uroliths were submitted in 2005 (Houston et al, 2006). In Hong Kong, Italy and Great Britain, struvite uroliths were the most common submission in the time period studied (1998 - 2000) with calcium oxalate second (Stevenson, 2001). In the Netherlands, calcium oxalate was the most common submission in the same time period with struvite uroliths second (Stevenson, 2001). Less frequently reported uroliths include ammonium urate, cystine, silica, xanthine, calcium phosphate, pyrophosphate and dried solidified blood uroliths.

Figure 4. Changing prevalence of calcium oxalate and struvite uroliths from 2001 to 2005. (Adapted from Forrester, 2006).

In male cats with obstructive FLUTD, urethral plugs are the number one cause followed by idiopathic cystitis (Figure 5) (Kruger et al, 1991). Less common causes of FLUTD in both male and female cats are those caused by anatomical defects, neoplasia, urinary tract infections and neurological disorders (Kruger et al, 1991). In cats older than 10 years, idiopathic cystitis is uncommon and urinary tract infection is the leading cause of FLUTD followed by urolithiasis (Figure 6) (Bartges, 1997). Bacterial cystitis is typically identified in cats less than one year of age, in older cats, and in cats with compromised host factors (perineal urethrostomies, diabetes mellitus, chronic kidney disease etc).

Figure 5. Percentage of obstructive causes of FLUTD in 51 male cats in the united states. (Adapted from Osborne et al, 2000).

Figure 6. Conditions responsible for the clinical signs of FLUTD in cats older than 10 years of age. (Adapted from Bartges 1997).