Pandora syndrome: Rethinking our approach to idiopathic cystitis in cats
Keeping cats indoors has become common veterinary advice to reduce the risk of exposure to infectious diseases and injury from vehicles or other animals. This advice may not be completely beneficial or even benign for cats, however. As early as 1925, "too close confinement to the house" was suggested to increase the risk of lower urinary tract signs (LUTS).1
Many factors associated with indoor housing and LUTS have been investigated. Excessive body weight and decreased activity were associated with increased risk in some studies, and cats that only had access to indoor litter pans had an increased risk of LUTS compared with cats that could eliminate outdoors.2 Living with other cats has also been associated with LUTS, suggesting that social interactions or a horizontally transmitted infectious agent might play a role in the development of these signs.2,3 The lack of difference between cases and controls in viral disease rates and the increase in risk associated with the amount of time spent indoors seem to argue against an infectious agent as a common cause.In addition to the factors listed above, one case-control study of cats with LUTS reported an increased incidence of LUTS in cats that moved into a new house within the previous three months and during winter months2 ; further analysis revealed a highly statistically significant association with rainy days during the previous month rather than with the season. Access to outdoor prey was found to be protective.
In addition to LUTS, studies have found indoor housing to be associated with a variety of other common diseases in cats.3 For example, dental disease is reported to be the most common disease in pet cats. Although indoor housing was not identified as a significant risk factor in one study, in a subsequent study, indoor housing was associated with a 4.5-fold increase in risk for gingivitis, calculus, or periodontal disease. Obesity in cats is also a common problem, and apartment dwelling, inactivity, certain dietary factors, and being middle-aged, male, neutered, and of mixed breeding have been associated with being overweight. Indoor housing has been associated with a 1.6- to 15.8-fold risk for obesity, depending on the parameter measured.3 One recent study reported that indoor confinement and physical inactivity—but not the proportion of dry food fed—were associated with increased risk for type 2 diabetes.4
These and other studies conducted over decades and around the world have identified indoor housing as a risk factor for disease in cats. Differences among studies, particularly those that did not find increased risk, might have occurred for a variety of reasons. The first, of course, being that indoor housing is not a risk factor. However, the fact that indoor housing has been associated with a variety of different diseases studied at different times and in different places seems to argue against this interpretation. Differences in sample sizes and the questions asked, undoubtedly, also contributed to the differences. Because the cats in most recent studies were all housed inside, nothing can be gleaned regarding the contributing factor of indoor housing. The identification of differences in breed susceptibilities also suggests that internal factors, including genetic (which genes are present) and epigenetic (which of the genes present that are expressed) factors, also influence risk.