Primary anestrus due to dietary hyperthyroidism in a miniature pinscher bitch

Abstract

A 2-year-old intact miniature pinscher bitch that had been on a bones and raw foods diet since birth showed no signs of estrus despite a 40-day course of cabergoline. Elevated levels of thyroxine were detected in the serum (51 nmol/L) and in the juice of the meat (183 nmol/L) fed to the dog. Change in diet and treatment with oral cabergoline resulted in signs of proestrus in 13 d, pregnancy, and normal birth of 5 puppies.

Primary anestrus in the female dog is defined as the absence of estrus signs by 18 to 24 months of age (1). The causes include previous ovariectomy or ovariohysterectomy, silent or missed heats, administration of certain drugs such as progestagens or glucocorticoids, abnormality of sexual differentiation, progesterone-secreting ovarian cysts, ovarian aplasia, systemic diseases, and immune-mediated oophoritis (1). Also, dysfunction of any part of the hypothalamic-pituitary-thyroid axis resulting in hypothyroidism, has been considered as one of the causes of infertility in the bitch (1,2). However, length of inter-estrus interval, duration of gestation, breeding behavior, interval between births of pups or serum progesterone concentrations and the pregnancy rate were similar in experimentally induced hypothyroid and euthyroid bitches in 2 recent studies (3,4).

Hyperthyroidism is not frequently seen in the dog and occurs most commonly due to neoplasm of the thyroid glands (5–9). Recently, hyperthyroidism was reported in 14 dogs fed bones and raw foods or biologically appropriate raw food (BARF) contaminated with thyroid glands (10,11).

The present report describes the clinical management of a case of primary anestrus due to food induced hyperthyroidism in a 2-year-old miniature pinscher female dog. To the authors’ knowledge, this is the first report on canine primary anestrus caused by intake of thyroid-contaminated food. Furthermore, the case is the first to report the effect of dietary hyperthyroid-ism on the canine reproductive system.

Case description

A 2-year-old, 4.6 kg, sexually intact miniature pinscher bitch was presented because of absence of estrus signs. The owner indicated that the mother of the bitch had the same complaint which resolved following a 2-week cabergoline treatment. Before presentation, the bitch had been taken to a private practice because of the same complaint and oral cabergoline (Galastop; Ceva Vetem S.p.a., Italy), 5 μg/kg body weight (BW), PO, q24h was prescribed for 40 d. This therapy failed to induce signs of estrus.

The bitch was housed inside and was routinely vaccinated and dewormed. The owner reported that the bitch had been on a BARF diet since she was born. The diet was based on cattle bones and meat of the head and neck region, always bought from the same local butcher. There was no history of lethargy, inappetence, vomiting, polydipsia, polyuria, diarrhea, or tenesmus. There was no previous medication except cabergoline.

On physical examination the bitch was bright and alert with normal appearance and conformation. The rectal temperature, pulse, and respiratory rates were within normal ranges. The vulva was of normal size and was not swollen. Vaginoscopy revealed edematous and hyperemic vaginal mucosa but no bloody vaginal discharge. A vaginal smear showed a predominance of parabasal and intermediate cells in the absence of red blood cells or superficial cells. Upon transabdominal ultrasonography (MyLab 20 Plus; Esaote S.p.a, Genova, Italy), the uterine diameter was 0.55 cm and the lumen did not contain any fluid (Figure 1). The ovaries were homogenous and isoechogenic. The right ovary had dimensions of 0.9 cm × 0.4 cm and the left ovary was 1.2 cm × 0.6 cm [normal size: 1.5 cm × 0.7 cm (12)]. No anechoic structures representing follicles were identified (Figure 1). Blood was collected for complete blood (cell) count (CBC) and for measurement of serum progesterone (P4), canine thyroid stimulating hormone (cTSH), and total thyroxine (T₄) concentrations. Serum P4 concentration was measured using a chemiluminescence assay (Immulite 1000; Siemens, Germany) validated for dogs (13). The detection limit of the assay is 0.20 ng/mL. Canine thyroid-stimulating hormone and total T₄ concentrations were also determined by chemiluminescence assay (Immulite 1000; Siemens) and the minimum detection limit of the assays were 0.01 ng/mL and 6.4 nmol/L, respectively. Immunological tests for the presence of antibodies against thyroglobulin, triiodothyronine (T₃), and T₄, using an enzyme immunoassay developed and validated for canine serum, were negative (14). Serum P4 concentration was 0.4 ng/mL and total T₄ concentration was 51.2 nmol/L (reference interval: 17.0 to 37.0 nmol/L). Plasma cTSH level was below the detection limit of the assay (normal values: < 0.6 nmol/L) (Table 1). No cervical mass could be palpated during the initial physical examination and absence of a mass of thyroid origin was confirmed by ultrasound examination. The owner was asked to provide a whole package of the BARF diet that was fed to the bitch and the same amount of cow muscle meat obtained from the same butcher to compare the levels of T₄ in both samples. The concentration of T₄ was much higher in the meat juice of the BARF diet compared to that of the muscle meat (183 nmol/L versus < 6 nmol/L).

Figure 1.

Ultrasonography images of the ovaries and the uterus of a 2-year-old, sexually intact miniature pinscher bitch, diagnosed with primary anestrus because of dietary hyperthyroidism. The images were taken on presentation (day 0; 1a, b and c), day 7 (2a, b and c), and day 21 (3a, b and c). The uterine diameter was measured on transverse view whereas sagittal view was used for the measurement of the ovaries.

Table 1.

Laboratory data for a 2-year-old, sexually intact miniature pinscher bitch with a history of lack of signs of estrus since she was born. Days are given after the diagnosis of primary anestrus

	Reference ranges	At presentation	D 13§	D 15	D 21	D 24	D 53
P4 (ng/mL)	< 1–2a
	> 2b	0.4	Onset of signs of proestrus	0.3	1.4	5.6	23.6
	4–10c
cTSH (ng/mL)	< 0.6	< 0.01		0.22	0.26	0.15	0.22
Total T4 (nmol/L)	17.0–37.0	51.20		24.10	37.3	41.70	33.4

cTSH — canine thyroid stimulating hormone; P4 — progesterone; and T₄ — thyroxine. Progesterone values:

^aduring anestrus until late proestrus,

^bat the time of LH surge, and

^cat ovulation. Values in bold are outside the reference interval.

^§Information obtained from the owner; no examination was performed.

The increased total T₄ level (51.2 nmol/L) in the serum and the undetectable cTSH concentration (< 0.01 ng/mL) were compatible with hyperthyroidism. Based on history, clinical examination, ultrasound and laboratory findings, a tentative diagnosis of primary anestrus due to dietary hyperthyroidism was made. Treatment consisted of immediately changing from the BARF diet to a commercial dog food and administration of cabergoline, 5 μg/kg BW, PO, q24h, for induction of estrus until proestral bleeding was observed. The bitch was closely monitored through serial examinations including vaginoscopy, vaginal cytology, and transabdominal ultrasonography of the ovaries and the uterus. Blood samples were collected during the examinations for the measurement of serum P4 concentration and the levels of thyroid hormones (Table 1).

The bitch was re-examined 7 d after the onset of therapy. Although uterine diameter was increased to 0.8 cm and anechoic structures were identified on both ovaries, there were no signs of proestrus (Figure 1). Thirteen days later, cabergoline treatment was stopped because the owner reported that signs of proestrus including vulvar bleeding, vulvar edema, and attraction to male dogs were observed. Physical examination performed 2 d after the onset of vulvar bleeding (15 d after diagnosis) identified a swollen vulva and hemorrhagic vulvar discharge. Vaginoscopy revealed edematous vaginal folds and hemorrhagic discharge from the cervix. The vaginal smear contained a predominance of red blood cells and intermediate cells and a few superficial cells. Transabdominal ultrasonography demonstrated an increase in the uterine diameter and in both ovaries. Serum P4 concentration was still < 1 to 2 ng/mL but the level of T₄ was within the reference interval (Table 1).

General examination, vaginoscopy, and vaginal cytology findings on days 21 and 24 were similar and revealed a less swollen vulva, a lighter vulvar hemorrhagic discharge, wrinkled and angulated vaginal mucosal folds, and dominance of superficial cells (> 90%). Several anechoic structures were seen in both ovaries (Figure 1). Serum P4 concentrations were 1.4 ng/mL and 5.6 ng/mL, respectively (Table 1). The level of T₄ was still above the upper cutoff despite discontinuation of the thyroid hormone intake. The luteinizing hormone (LH) peak and ovulation are believed to occur between days 21 and 24.

The bitch was naturally bred 2 times on the 27th and 28th days after the diagnosis and therapy (14 and 15 d after the onset of proestral bleeding) by a male of the same breed. Twenty-five days after the second mating (53 d after the diagnosis and therapy), 5 fetal vesicles with a normal heart beat of > 200 beats/min were detected ultrasonographically. Serum P4 concentration was within the normal range for canine gestation and the levels of cTSH and T₄ were within reference intervals (Table 1) (15). The bitch gave birth to 4 male puppies and 1 female puppy on day 62 following ovulation without any need for assistance. The owner indicated that parturition was completed within 2 h.

Discussion

In the current case, the hyperthyroidism was most likely due to the consumption of contaminated BARF diet which has been recently documented in dogs (10,11). Presence of a thyroid neoplasm or ectopic or intra-thoracic thyroid tissue was unlikely because of the young age of the dog, absence of a palpable mass in the cervical region, lack of other clinical signs such as polyuria and polydipsia, and normalization of the T₄ levels following the change in diet (5–7,16). Although storage of canine blood at high temperatures for more than 5 d may give higher than normal T₄ concentrations (17), all the samples in this case were processed immediately after collection. The negative tests of thyroid autoimmunity excluded thyroiditis or interference of antibodies with the hormone immunoassay measurements resulting in falsely elevated levels (8). Furthermore, fresh thyroid glands have been given orally to humans and animals for centuries to cure hypothyroidism before appropriate drugs were developed (18,19). On the other hand, the previous long-term use of cabergoline before presentation might have been the cause of undetectable concentration of cTSH in the bitch presented here; cabergoline administration for at least 4 mo in humans and 3 wk in male dogs resulted in a significant decrease in TSH release and thus a reduction in levels of T₄ (20–22). Higher than normal levels of T₄ in the case reported here was probably due to the exogenous intake of thyroid hormones.

Thyrotoxicosis factitia or hyperthyroidism due to the intake of excessive quantities of thyroid hormones via consumption of thyroid-contaminated meat or by taking excessive doses of thyroid hormone preparations has also been reported in humans as individual cases or as outbreaks (23–27). The reproductive consequences of alimentary hyperthyroidism in women are oligomenorrhoea and decreased fertility whereas reduced libido occurs in men (28,29). The most likely cause of hyperthyroid-ism in the current case was the thyroid contaminated BARF diet which was demonstrated by normalization of the thyroid hormones following the diet change. The diagnosis of the condition in most of the cases in humans is simply made from the history and confirmed by the disappearance of the symptoms following cessation of the thyroid supplementation (30). Higher thyroid hormone level in the contaminated head meat sample compared to the sample from the muscle tissue in the current case is further support for the diagnosis of thyrotoxicosis (25). Thyroid contamination likely occurs when the butchers do not remove the thyroid glands while harvesting the meat from the neck (11). Although elevated concentration of T₄ in the serum and in the meat juice and undetectable cTSH were suggestive of diet related hyperthyroidism in the current case, a pre-existing thyroid pathology cannot be ruled out since a biopsy, which is considered as the “gold standard” for the diagnosis of hyperthyroidism, was not performed (7,29).

An inconsistency between “primary anestrus” in the current case and the findings of vaginoscopy (an edemateous and hyperemic vaginal mucosa) and vaginal cytology (predominance of parabasal and intermediate cells) might be due to elevated estrogen secretion, a condition which has been reported in women with thyrotoxicosis (31). These women had significantly higher total immunoreactive estrogen concentrations compared to euthyroid females and in 30% of the patients estrogen peaks were not followed by an LH peak (31). Furthermore, the changes seen in the vaginal mucosa and vaginal smears might be the result of the 40-day course of cabergoline (32).

Amenorrhea in a woman of reproductive age is one of the earliest reported clinical changes occurring due to hyperthyroidism (28,29,33). Exogenous hyperthyroidism caused by thyroid-contaminated diet appears to be the cause of primary anestrus in the bitch reported here as well, because most of the other reported causes of primary anestrus were ruled out by close observation of the owner, a detailed anamnesis, and clinical, laboratory, and imaging examinations (1). Furthermore, the fact that the 40-day course of cabergoline treatment failed to induce signs of estrus during the intake of thyroid-contaminated diet but was successful when the diet was switched to a commercial dog food, confirms this hypothesis. However, it is unknown whether proestrus would have spontaneously occurred in the bitch reported here without the use of cabergoline following the change of diet since no reports regarding diet induced primary anestrus in the bitch have been published.

It is difficult to explain the mechanism responsible for lack of signs of estrus for 2 y in the bitch presented here. The hypothalamic-pituitary-gonadal axis and the hypothalamic-pituitary-thyroid axis are believed to influence each other by cross-talk which results in fertility problems in humans (33,34). Moreover, thyroid hormones indirectly affect the menstrual pattern through their influence on gonadal steroid hormone binding proteins, prolactin and gonadotropin-releasing hormone (GnRH) secretion, and coagulation factors and also directly through their impact on the gonads (34). Hormonal changes seen in hyperthyroid women include increased concentrations of estrogens, testosterone, and rostenedione as well as their binding proteins (31,33,34). Despite an elevation in the GnRH-induced LH secretion in hyperthyroid women, LH peaks are absent in women with amenorrhea (31,34). It is believed that the feedback effects of estrogen on the hypothalamo-pituitary LH releasing region are diminished in patients with thyrotoxicosis (31). This could be true for the dog reported here as well because of the lack of any increase in serum P4 concentrations that corresponds to the time of LH peak in repeated blood samples (35). Interestingly, daily use of levothyroxine orally in healthy bitches induced signs of proestrus in 70% to 80% of the cases in which a conception rate of 57% was achieved in a recent study (36).

In cases of dietary hyperthyroidism, immediate change of BARF diet to commercial dog food resulted in disappearance of the clinical signs within several days and normalization of plasma thyroid hormone levels within 8 wk without further treatment (10,11), which was also seen in the current case. However, T₄ concentrations were still higher than normal on days 21 and 24 despite stopping the BARF diet. This could be due to the time required for the thyroid gland to fully recover following chronic consumption of thyroid contaminated diet, the daily fluctuation of the thyroid hormones, or to pregnancy (37,38). In a single case report (38), acute levothyroxine over- dosage resulted in persistence of elevated T₄ concentrations for up to 36 d. Prognosis of dietary hyperthyroidism seems to be excellent as no recurrence of clinical signs has been reported after the change in diet.

In conclusion, a detailed history including diet is required to determine and treat the underlying cause of primary anestrus in the dog. Feeding a diet contaminated with thyroid hormones should be considered as a cause of canine primary anestrus. The owners, particularly breeders, should be warned about the possible detrimental effects of thyroid contaminated BARF diet on the estrous cycle. CVJ