Page 984 - Small Animal Internal Medicine, 6th Edition

956 PART VIII Reproductive System Disorders

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A B

FIG 55.3
Gross specimen showing multiple luteal cysts found in one ovary of a bitch with prolonged
diestrus and eventual pyometra. (A) Intact ovary. (B) Sectioned ovary.

markedly elevated FSH and LH concentrations, as would
be seen after ovariohysterectomy. Such increases indicate a
lack of negative feedback to the pituitary and hypothalamus,
without any other identifiable cause for anestrus. Immune-
mediated oophoritis, diagnosed by ovarian histopathology,
could result in prolonged anestrus. A mononuclear infil-
trate predominated by lymphocytes, plasma cells, and mac-
rophages has been reported to occur in both ovaries in a
bitch experiencing estrous cycle abnormalities. This is an
extremely rare disorder.
Hypothyroidism is a potential cause for prolonged inter-
estrous intervals or failure to cycle, but the diagnosis should
be well supported by other clinical signs (lethargy, weight
gain, bilaterally symmetric alopecia) and clinical pathologic
FIG 55.4 data (hypercholesterolemia, nonregenerative anemia), as
Gross specimen, same bitch, cystic endometrial hyperplasia. well as confirmation of subnormal serum thyroid (total
T 4 and free T 4 by equilibrium dialysis) concentrations,
ideally supported by elevated endogenous canine thyroid-
resolution of follicular cysts. Cystic endometrial hyperplasia, stimulating hormone (cTSH) concentrations (see Chapter
if present, may resolve partially after elimination of the cyst 48). Bitches with circulating antithyroid antibodies may have
but still contributes to subfertility (Fig. 55.4). Unfortunately, artificially elevated total T 4 concentrations due to cross-
concern exists that uterine biopsy during diestrus could con- reactivity. Hypothyroid bitches placed on adequate replace-
tribute to pyometra (Schlafer and Gifford, 2008). ment therapy should begin to cycle within 6 months of
Nonfunctional ovarian cysts may cause failure to cycle becoming euthyroid. The presence of immune-mediated
owing to their mass effect. Rete ovarii cysts and subsurface thyroiditis is thought to have a genetic basis in some breeds
epithelial structure cysts are examples of nonfunctional and may occur with other immune-mediated endocrinopa-
ovarian cysts. Increases in plasma estrogen or progesterone thies. Currently this is evaluated by periodic measurement
concentrations will not be identified, although these cysts of thyroglobulin autoantibodies (TGAA). The breeding
have the potential to produce a wide variety of other steroidal soundness of such bitches should be addressed with clients.
compounds without apparent systemic effect. This diagnosis, Glucocorticoids can feed back on pituitary gonadotropins
initially suspected using abdominal ultrasonography, is con- FSH and LH, causing a failure to cycle, so administration of
firmed by histologic evaluation of surgically removed tissues. any steroid medication must be discontinued by taper in a
Premature ovarian failure can result in permanent anes- bitch with prolonged anestrus.
trus. Although the functional longevity of the ovaries of
bitches is not known, on average the decline in function SHORTENED INTERESTROUS INTERVALS
would not be expected before 7 to 10 years of age. Bitches Bitches with short (<4.5 months) interestrous intervals can
can reproduce late in life. Prolonged anestrus due to pre- fail to conceive because of incomplete uterine involution
mature ovarian failure could be supported by documenting and repair, precluding implantation. Classically, bitches