Pyometra is a disease of the middle-aged or older animal.
The mean age of pyometra diagnosiswas 4 years in our
study. This is similar to a previous report [6] but different
from the median age of 7.2 years in another [2]. Because
clear differences in breed and age exist, variations between
different studies may depend on the selection of cats
included in each study population. The present study is the
only one based on the cat population at large which minimizes
such effects. A small peak in the curve displaying IRs
was observed after 9 years of age (Fig. 1). It could be
speculated whether this increase is related to degenerative
changes in the uterus or other conditions such as ovarian
pathologies or uterine neoplasia that more often affect
older animals and may predispose for developing pyometra.
Uterine neoplasia is rare in cats, with a median age for
diagnosis of 9 years, but it has been described also in
younger cats [18–20]. Endometrial hyperplasia, on the
other hand, is common in older cats, and this condition is
regarded as potentially precancerous in humans [17,21].
Expression of the HER-2/neuoncoprotein, which is associated
with proliferation and has prognostic importance for
human endometrial cancer, was increased in the endometrium
and glandular epithelium of uteri from cats with
pyometra in one study [21]. Unless histological examination
is performed, less severe neoplastic conditions of the
uterus may be undetected because inflammatory uterine
wall enlargement could appear macroscopically similar.
Whether pyometra and neoplasia are induced simultaneously
as has been observed in some cats or whether
neoplasia precedes pyometra or vice versa remains to be
determined [18–21].