Evaluation of serum prolactin level in patients of subclinical and overt hypothyroidism

Systematic review of the association between thyroid disorders and hyperprolactinemia

INTRODUCTION

Thyroid disease (TD), particularly hypothyroidism, is an important etiology of hyperprolactinemia (HPRL). We conducted a systematic review of the clinical characteristics, management, and outcomes of adults (> 18 years) with this clinical association.

MATERIALS AND METHODS

We searched PUBMED, SCOPUS, and EMBASE to find eligible articles published in English from any date till 15th December 2022.

RESULTS

The final systematic review included 804 patients from 47 articles, of which the majority (85.9%) were females. Menstrual irregularity was the most prominent symptom of HPRL (74.3%). Subclinical hypothyroidism (57.1%) was the most reported TD. Individual patient data were available for 62 patients from 35 studies. The median age was 32 (25-42) years, TSH was 110.25 (50-345.4) mU/L, and PRL level was 60 (37.6-91) ng/ml. On treating TD, 38 (70.4%) patients had complete resolution and 10 (18.5%) had an improvement in HPRL. Of 38 patients with pituitary imaging, 26 (68.4%) showed pituitary enlargement, and 13 (34.2%) showed a suprasellar extension. 13 (76.5%) patients had complete resolution and 3 (17.6%) had an improvement in pituitary enlargement on TD treatment. A positive correlation was observed between higher serum TSH levels and higher serum prolactin levels. Patients with pituitary enlargement on imaging had a higher TSH level compared to those without any pituitary enlargement (Median of 263 (61-602) vs. 50 (24.3-128) mU/L; p-value = 0.01).

CONCLUSION

Thyroid hormone replacement can lead to resolution of HPRL and pituitary enlargement in the majority of patients with HPRL due to overt or subclinical hypothyroidism without the need for dopamine agonist treatment.

Increase in Thyrotropin Is Associated with an Increase in Serum Prolactin in Euthyroid Subjects and Patients with Subclinical Hypothyroidism

Background: Prevalence and clinical significance of hyperprolactinemia in subclinical hypothyroidism have been reported in few studies. The upper limit of the normal range for TSH used to diagnose subclinical hypothyroidism is a matter of controversy. Some experts believe that the upper limit of the normal TSH range should be reduced from 4.2 to 2.5 mIU/L. Some evidence suggests a positive relationship between TSH > 2.5 mIU/L and cortisol as an indicator of metabolic stress. With this view prolactin as a stress hormone can be elevated in TSH >2.5 in comparison to TSH< 2.5. Hence the aim of this study was to evaluate the relationship between TSH and prolactin levels in the TSH range <10.

Methods: This cross-sectional study was performed on apparently healthy subjects with TSH<10 mIU/L. Subjects with the age of 18 to 35 years were enrolled. The sera were analyzed for prolactin, FT3, FT4, TSH, TPO-Ab and Tg-Ab.

Results: From the total number of 519 participants, in 65 subjects (12.5%) TSH was < 2.5. Seventy-nine subjects (15.2%) had TSH: 2.5-4.2 and 375 (72.3%) of the participants had TSH> 4.2 mIU/L. The mean age, weight and BMI of subjects in the three TSH groups were not significantly different. In the three TSH groups, the prevalence of hyperprolactinemia was zero, 3.8 and 30.7%, respectively. There was a positive and significant correlation between prolactin and TSH levels (r=0.613).

Conclusion: Hyperprolactinemia is common in patients with subclinical hypothyroidism (30.7%) and there is a positive correlation between TSH and PRL in subjects with TSH<10 mIU/l.

A New Perspective on Thyroid Hormones: Crosstalk with Reproductive Hormones in Females

Accumulating evidence has shown that thyroid hormones (THs) are vital for female reproductive system homeostasis. THs regulate the reproductive functions through thyroid hormone receptors (THRs)-mediated genomic- and integrin-receptor-associated nongenomic mechanisms, depending on TH ligand status and DNA level, as well as transcription and extra-nuclear signaling transduction activities. These processes involve the binding of THs to intracellular THRs and steroid hormone receptors or membrane receptors and the recruitment of hormone-response elements. In addition, THs and other reproductive hormones can activate common signaling pathways due to their structural similarity and shared DNA consensus sequences among thyroid, peptide, and protein hormones and their receptors, thus constituting a complex and reciprocal interaction network. Moreover, THs not only indirectly affect the synthesis, secretion, and action of reproductive hormones, but are also regulated by these hormones at the same time. This crosstalk may be one of the pivotal factors regulating female reproductive behavior and hormone-related diseases, including tumors. Elucidating the interaction mechanism among the aforementioned hormones will contribute to apprehending the etiology of female reproductive diseases, shedding new light on the treatment of gynecological disorders.

Genetic Susceptibility to Joint Occurrence of Polycystic Ovary Syndrome and Hashimoto's Thyroiditis: How Far Is Our Understanding?

Polycystic ovary syndrome (PCOS) and Hashimoto’s thyroiditis (HT) are endocrine disorders that commonly occur among young women. A higher prevalence of HT in women with PCOS, relative to healthy individuals, is observed consistently. Combined occurrence of both diseases is associated with a higher risk of severe metabolic and reproductive complications. Genetic factors strongly impact the pathogenesis of both PCOS and HT and several susceptibility loci associated with a higher risk of both disorders have been identified. Furthermore, some candidate gene polymorphisms are thought to be functionally relevant; however, few genetic variants are proposed to be causally associated with the incidence of both disorders together.

Assessment of subclinical hypothyroidism for a clinical score and thyroid peroxidase antibody: a comparison with euthyroidism grouped by different thyroid-stimulating hormone levels

Background

Subclinical hypothyroidism (SCH) might have many symptoms of hypothyroidism. The controversy appears to lower the level of thyroid-stimulating hormone (TSH) and group subjects with TSH of more than 3 or even 2.5 mIU/L as SCH subjects.

Objectives

To assess SCH subjects both clinically using Zulewski clinical score and biochemically and to evaluate whether the euthyroid subjects with high-normal TSH (HNT) have any clinical symptom or subnormal biochemical finding.

Methods

A prospective cross-sectional study of 233 subjects, 67 with SCH and 166 euthyroidism, was conducted. Euthyroid subjects were divided according to the level of TSH as HNT (>2.5 mIU/L) and low-normal TSH (0.5–2.5 mIU/L). The subjects were examined for clinical feature including Zulewski clinical score and biochemical evaluations including thyroid peroxidase antibody (TPO-Ab) titer. The comparisons between groups were assessed using independent sample t test, and correlations between variables were evaluated using Pearson correlation.

Results

A significantly higher clinical score and higher frequencies of symptoms were found in the SCH group compared to the euthyroid group. The most frequent symptom was fatigue. Euthyroid subjects with HNT were found to have higher TPO-Ab titers than those with low-normal TSH, P < 0.05. The Zulewski clinical score was positively correlated with TSH and TPO-Ab titer but negatively correlated with the FT4 level, P < 0.05.

Conclusions

Zulewski clinical score is higher in SCH subjects compared to euthyroid subjects and can aid in assessing SCH subjects. A significant correlation exists between Zulewski clinical score and each of the TSH, FT4, and TPO-Ab titer levels. The frequency of TPO-Ab positivity is high in SCH. Additionally, euthyroid with higher TSH levels has higher level of TPO-Ab titer but not higher clinical score.

The Unexplored Crossroads of the Female Athlete Triad and Iron Deficiency: A Narrative Review

Despite the severity and prevalence of iron deficiency in exercising women, few published reports have explored how iron deficiency interacts with another prevalent and severe condition in exercising women: the 'female athlete triad.' This review aims to describe how iron deficiency may interact with each component of the female athlete triad, that is, energy status, reproductive function, and bone health. The effects of iron deficiency on energy status are discussed in regards to thyroid function, metabolic fuel availability, eating behaviors, and energy expenditure. The interactions between iron deficiency and reproductive function are explored by discussing the potentially impaired fertility and hyperprolactinemia due to iron deficiency and the alterations in iron metabolism due to menstrual blood loss and estrogen exposure. The interaction of iron deficiency with bone health may occur via dysregulation of the growth hormone/insulin-like growth factor-1 axis, hypoxia, and hypothyroidism. Based on these discussions, several future directions for research are presented.

Impact of Triclosan on Female Reproduction through Reducing Thyroid Hormones to Suppress Hypothalamic Kisspeptin Neurons in Mice

Triclosan (TCS), a broad-spectrum antimicrobial agent, is widely used in clinical settings and various personal care products. The aim of this study was to evaluate the influence of TCS on reproductive endocrine and function. Here, we show that the exposure of adult female mice to 10 or 100 mg/kg/day TCS caused prolongation of diestrus, and decreases in antral follicles and corpora lutea within 2 weeks. TCS mice showed decreases in the levels of serum luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone, and gonadotrophin-releasing hormone (GnRH) mRNA with the lack of LH surge and elevation of prolactin (PRL). TCS mice had lower kisspeptin immunoreactivity and kiss1 mRNA in anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC). Moreover, the estrogen (E2)-enhanced AVPV-kisspeptin expression was reduced in TCS mice. In addition, the serum thyroid hormones (triiodothyronine (T3) and thyroxine (T4)) in TCS mice were reduced with increases in levels of thyroid stimulating hormone (TSH) and thyroid releasing hormone (TRH). In TCS mice, the treatment with Levothyroxine (L-T4) corrected the increases in PRL, TSH and TRH; the administration of L-T4 or type-2 dopamine receptors agonist quinpirole inhibiting PRL release could rescue the decline of kisspeptin expression in AVPV and ARC; the treatment with L-T4, quinpirole or the GPR45 agonist kisspeptin-10 recovered the levels of serum LH and FSH and progesterone, and GnRH mRNA. Furthermore, TCS mice treated with L-T4 or quinpirole resumed regular estrous cycling, follicular development and ovulation. Together, these results indicate that exposing adult female mice to TCS (≥10 mg/kg) reduces thyroid hormones causing hyperprolactinemia that then suppresses hypothalamic kisspeptin expression, leading to deficits in reproductive endocrine and function.

Estimation of serum prolactin levels and determination of prevalence of hyperprolactinemia in newly diagnosed cases of subclinical hypothyroidism

Background:

Hyperprolactinemia is a common endocrine disorder involving hypothalamic–pituitary axis. Prolactin (PRL) secretion is stimulated by dopamine antagonism and thyroid-releasing hormone. Hyperprolactinemia has been reported in subclinical hypothyroidism (SCH) but results are markedly variable and studies on SCH are very few. The objective of this study was to find out prevalence of hyperprolactinema in newly diagnosed subclinical hypothyroid patients.

Materials and Methods:

In this cross-sectional study, serum PRL levels of 150 newly diagnosed subclinical hypothyroid patients were determined using electrochemiluminescence method.

Results:

Raised PRL levels were found in 18 (%) patients with SCH. There was positive correlation between serum thyroid-stimulating hormone and PRL levels. Prevalence of infertility was significantly higher with presence of hyperprolactinemia than normoprolactinemia in subclinical hypothyroid patients.

Conclusion:

Routine prolactin estimation and subsequent treatment is required in patients with subclinical hypothroidism.