Hypoluteoidism in a dog associated with recurrent mammary fibroadenoma stimulated by progestin therapy

Background Hypoluteoidism in the bitch is characterized by insufficient production and secretion of progesterone by the corpora lutea. It is a rare pathologic condition and during pregnancy, it leads to embryonic resorption or fetal abortion. Supplementary therapy with progestins is indicated during pregnancy to obtain delivery of vital puppies but unwarranted side effects of such treatment are poorly documented. Case presentation A 4-year-old, nulliparous, female Istrian Shorthaired Hound dog had been mated repeatedly in six heats with different dogs of proven fertility but signs of pregnancy did not develop. Estrous cycles, mating and pregnancies were monitored as hypoluteoidism or genital disease was suspected. During the first monitored estrus, the bitch was mated and on day 18 [day 0, day of estimated peak of luteinizing hormone (LH)], ultrasound examination showed three amniotic vesicles that were however found to be resorbed between day 20 and 23. Progesterone concentrations, measured by ELISA, were >8 ng/mL until day 12 and 1–2.5 ng/mL on days 20, 23 and 26. Primary hypoluteoidism was therefore suspected. In the second monitored estrus, the bitch was mated and during pregnancy, progesterone concentrations were >8 ng/mL until day 17 and 1–2.5 ng/mL on day 19. On days 20 and 22, two out of three embryonic vesicles had been resorbed. The bitch was treated with progesterone in oil from day 19 to day 58. Increase in the size of 2nd left thoracic mammary gland (T2-L) was observed and on day 46, ultrasound evaluation and biopsy were performed revealing a low-cellularity fibroadenoma. Parturition started spontaneously at day 65 but due to dystocia caused by fetal macrosomia, a Caesarean section was performed. During the next (third) monitored estrus, the bitch was bred again and during pregnancy, early decrease in progesterone concentration confirmed the diagnosis of primary hypoluteoidism. The bitch was treated with synthetic progestin (altrenogest) from day 8 to day 57. Five amniotic vesicles were detected by ultrasonography. Recurrence of swelling of T2-L was observed. On day 60, the bitch whelped five pups, two males and three females. As reported later by the owner, the latter did not show any sign of heat over the past 3 years. In one of them, clitoral hypertrophy and a blind ending vagina were diagnosed. Conclusions This is the first description of early hypoluteoidism in a pregnant bitch developing a mammary fibroadenoma under progestin treatment.