CHAPTER 22 ENDOCRINOPATHIES, ATYPICAL 339
Estrogen Imbalances
Estrogen is produced by ovarian follicles and cysts, Leydig and Sertoli cells of the
testes, and zona glomerulosa and fasciculata of the adrenal gland.
Estrogen is an inhibitor of anagen initiation in dogs (stimulates scalp hair growth in
human beings) and potentiates the action of androgens in the prostate and proges-
terone in the endometrium.Animals with normal serum estrogen concentrations may have increased numbers of
estrogen receptors in the skin.
Peripheral conversion of estrogen and/or excess androgens, as well as regulation of
hormone receptors, is affected by growth factors; abnormalities may cause estrogen
excess or deficiency.True estrogen deficiency is uncommon; it is primarily seen following ovariohysterec-
tomy; serum estradiol concentrations may be normal.
Younger intact female dogs (ovarian cysts) (Figure 22.7).
Older intact female dogs (granulosa cell tumor, other ovarian tumor, ovarian cysts).
Older intact male dogs: testicular tumors (Sertoli cell tumor, seminoma, or interstitial
cell tumor); boxer, Shetland sheepdog, weimaraner, German shepherd, cairn terrier,
pekingese, collie; increased risk in cryptorchid dogs (Figures 22.8, 22.9).Intact or altered female and male dogs (exogenous administration of diethylstilbe-
strol) (Figure 22.10).
Exposure to topical hormone replacement therapy by owner (Figures 22.11, 22.12).
Hyperestrogenism associated with:
Enlargement of nipples, mammary glands, vulva, prepuce
Linear preputial dermatitis; testicles may palpate normal or irregular in size
Petechiae due to thrombocytopenia
Pyrexia due to neutropenia.
Hyperandrogenism and Hyperprogesteronemia
Elevated level of progesterone has been associated with alopecia; most often caused
by exogenous administration – megestrol acetate or exposure to topical hormone
replacement therapy by owner (Figure 22.13).Progesterone effect likely due to binding of glucocorticoid receptors and/or conver-
sion to cortisol within canine hair follicles.
Castration-responsive alopecia as well as testosterone-responsive alopecia may result
from proximate relative changes in hormone levels; response may not persist.
Hyperandrogenism (primarily males): uncommon to rare cause of alopecia in middle-
aged to old intact dogs; may cause tail gland hyperplasia (Figure 22.14).
Exposure to topical hormone replacement therapy by owner (Figure 22.15).
SIGNALMENT/HISTORY
Hair coat: dry or bleached because hairs are not being replaced; lack of normal shed;
usually diffuse and bilaterally symmetrical truncal alopecia sparing the head and