Vaginal cytology as a diagnostic tool (Proceedings)
Normal physiologic conditions
Proestrus / estrus
History = Time is correct for onset of estrous cycle.Physical examination findings = Turgid vulvar swelling is present in proestrus. Classically, the vulva softens in estrus (standing heat).
Gross appearance of discharge = The discharge is serosanguinous in proestrus and classically changes to a straw color during estrus. At no time should it have a foul odor.
Microscopic appearance of discharge = Over the period of proestrus, there will be an increase in percentage of the vaginal epithelial cells that are cornified and a decrease in number of PMNs. The classic definition of estrus by cytology is complete cornification with greater than 50% of the cells being anuclear squames, and an absence of PMNs.
Miscellaneous = Male dogs may be attracted but the bitch is not interested in proestrus. Estrus is defined by the bitch's behavior, as she allows the male to mount and breed.
Diagnostic tests to confirm = None usually are needed. Serial vaginal swabs and measurement of concentration of progesterone in serum may be needed to differentiate proestrus from diestrus.
Late pregnancy / parturition
History = The bitch is due to whelp soon or is at term. Remember that gestation length from breeding date can vary from 58 to 71 days.
Physical examination findings = Mammary development may be present and milk may be expressed. This occurs in some bitches up to a week before whelping; conversely, some primiparous bitches have no discernible mammary development at the time of parturition.
Gross appearance of discharge = Scant mucoid discharge of variable amounts may be exuded intermittently in the week before whelping. At the time of parturition, passage of clear, slightly blood-tinged or slightly brown fluid is normal. Green coloration indicates placental separation has occurred. Frank hemorrhage never is normal. Vulvar discharge at the time of parturition never should be foul-smelling.
Microscopic appearance of discharge = This is a non-inflammatory discharge. Red blood cells and occasional healthy PMNs may be present.
Miscellaneous = Bitches in labor should be showing other clinical signs, including restlessness, panting, vomiting and overt abdominal contractions as they enter Stage II labor. Monitoring systems (WhelpWise, for example) may be required to determine if uterine contractions are occurring.
Diagnostic tests to confirm = Serum progesterone concentration must fall to less than 2 ng/ml for a bitch to have effective uterine contractions. Measurement of progesterone may help set the mind of a worried owner at rest in the week prior to parturition, especially if the bitch is carrying a large litter and is uncomfortable. Patency of the cervix cannot routinely be determined by digital vaginal examination. Determination of gestational age of the pups is possible with radiography; if teeth are visible, the bitch is within 4 days of whelping.
History = Lochia is the normal postpartum discharge of the bitch. It may be present for up to 3 weeks after parturition.
Physical examination findings = Mammary development is present and milk can be expressed from the mammary glands.
Gross appearance of discharge = The discharge varies in color from green to black to red. It should not be frankly hemorrhagic, should not be foul-smelling and should decrease in volume over time.
Microscopic appearance of discharge = The discharge is non-inflammatory.
Ovarian follicular cysts
History = This is most common in young bitches. Combined length of proestrus and estrus is greater than 6 weeks.
Physical examination findings = The bitch has the clinical appearance of proestrus or estrus.
Gross appearance of discharge = The discharge usually is serosanguinous and has no foul odor.
Microscopic appearance of discharge = The vaginal epithelial cells are completely cornified and may appear ragged. PMNs are not present; bacteria may be visible, adhered to the surface of the epithelial cells.
Miscellaneous = This condition obviously only occurs in intact bitches. Young bitches with follicular cysts and subsequent anovulation on one cycle often cycle normally the next time. Follicular cysts are hereditary in cattle; hereditary basis in dogs is not known. Bitches under the influence of estrogen for a long time that then are induced to ovulate may be predisposed to cystic endometrial hyperplasia and pyometra (see below).
Diagnostic tests to confirm = Serial vaginal cytology is unchanging. The only rule-out for prolonged estrus in bitches is a functional granulosa cell tumor; these usually arise from the ovaries of older bitches and often are so large as to be palpable per abdomen or visible on radiographs or ultrasound. Often, response to treatment is used for diagnosis.
Treatment = Ovulation induction with gonadotropin releasing hormone (GnRH; 50 mcg IM).