Figure 1: Struvite (magnesium ammonium phosphate) urolith removed from the urinary bladder of a 4-year-old male domestic shorthair
cat.
The sustained increase in occurrence of struvite uroliths from 2003 to 2006 may be associated with decreased use of diets
designed to dissolve sterile struvite uroliths as a consequence of the significant increase in occurrence of calcium oxalate
uroliths in the 1980s and 1990s. However, it is likely that many of the 5,001 sterile struvite uroliths obtained from cats
and submitted to the Minnesota Urolith Center in 2006 could have been readily dissolved in two to four weeks by feeding a
diet designed to promote formation of urine that is under-saturated with struvite.
Epidemiology of feline urethral plugs: 1981-2006
Table 2 Feline urolith distribution 1981-2006
Table 3 Feline plug distribution 1981-2006
Of 551 urethral plugs submitted to the Minnesota Urolith Center by veterinarians in 2006, the mineral composition of about
87 percent was primarily struvite (Table 1; Figure 2). Approximately 1 percent were composed of calcium oxalate. Since 1981,
struvite has consistently been the most-common mineral in feline urethral plugs; the prevalence of calcium oxalate in urethral
plugs always has been infrequent (Table 3). The explanation as to why there have been significant shifts in the prevalence
of calcium oxalate and struvite in feline uroliths during the past 25 years, while the prevalence of struvite and calcium
oxalate in feline urethral plugs has not significantly changed is not obvious to us. We invite our readers to submit their
thoughts on this apparent paradox. Whatever the reason(s), the high prevalence of struvite in urethral plugs is of clinical
significance in terms of the design of dietary strategies to prevent their formation.
Additional information may be obtained at
http://www.cvm.umn.edu/ Click on the link to "Department and Centers" to find Minnesota Urolith Center.
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