Hypothyroidism
David S. Cooper, Jennifer A. Sipos in Medical Management of Thyroid Disease, 2018
Hypothyroidism, at the most basic level, is a state of deficient thyroid hormone action in tissues that are dependent on thyroid hormone for normal function. Numerous medications can impair thyroid function, causing primary hypothyroidism; the most notable of these are amiodarone, lithium, alpha interferon, and tyrosine kinase or multikinase inhibitors. Hypothyroidism is also classified accordingly into three degrees of severity, although thyroid failure clearly exists on a continuous spectrum of severity. Measurement of the serum thyroid stimulating hormone (TSH) level is the most sensitive and accurate test for detecting primary hypothyroidism. Current recommendations for screening for hypothyroidism vary greatly across organizations because of insufficient evidence that identifying and treating asymptomatic mild hypothyroidism is beneficial. Treatment of hypothyroidism involves thyroid hormone replacement in quantities sufficient to relieve symptoms and return serum TSH levels into the normal range. Treatment of patients with overt hypothyroidism results in the rapid resolution of most hypothyroid symptoms in the majority of patients.
Anaplastic thyroid carcinoma and thyroid lymphoma
David S. Cooper, Jennifer A. Sipos in Medical Management of Thyroid Disease, 2018
This chapter discusses the diagnosis and management of anaplastic thyroid cancer’s (ATCs) and primary thyroid lymphomas (PTL). Aggressive tumors such as ATC and PTL tend to present similarly, most often with a symptomatic rapidly growing neck mass requiring expeditious evaluation, diagnosis, and therapy. In single institutional studies, the presence of differentiated thyroid cancer (DTC) component, younger patient age, and earlier tumor stage at the time of diagnosis have been associated with better prognosis. ATC primary tumors are typically hard, poorly circumscribed, and fixed to surrounding structures. In the Mayo Clinic series, 60% presented as a multinodular goiter and 38% presented as an apparently unifocal thyroid mass; only 2% caused diffuse thyroid enlargement. Diagnostic scanning with radioiodine is not indicated in ATC and can delay diagnosis, but it is sometimes helpful later in the disease course in the event of recurrent coexistent DTC.
Surgical approach to thyroid disorders
David S. Cooper, Jennifer A. Sipos in Medical Management of Thyroid Disease, 2018
Surgery for the thyroid gland began pre-Renaissance and was advanced with modern techniques by renowned surgeons, including Theodor Kocher, Billroth, and Halstead. The strap muscles are reapproximated with a running 3–0 vicryl stitch, making sure to re-oppose the fascia over the musculature appropriately and leave a space inferiorly. It is then important to verify the absence of any further bleeding within the subplatysmal space before closing the skin with 3–0 vicryl subdermal sutures. Restrictions on strenuous activity and diet as well as bathing instructions are important for good wound healing in the first few weeks after surgery. The majority of patients with thyroid nodules are managed conservatively with serial sonographic examinations. The incidence of differentiated thyroid cancer is increasing faster than any other malignancy; however, overall survival remains stable. The diagnosis of medullary thyroid carcinoma can be challenging on fine needle aspiration as cytology is often indeterminate.
PROSTATE-THYROID AXIS: PROSTATIC TRH IS ONE OF THE STIMULATORS OF THYROID HORMONE
Published in Endocrine Research, 2001
R. R. M. Maran, K. Ravichandran, J. Arunakaran
Ventral prostatectomy decreased serum thyroid hormones and histology of the thyroid gland indicate that hypothyroid condition. Co-culture of thyroid gland and ventral prostate stimulates thyroid hormone secretion. In the present study we report prostatic thyrotropin releasing hormone (TRH) is the stimulating factor of thyroid hormone secretion. Mature rat (90 days old) ventral prostate, anterior pituitary and thyroid glands were co-cultured in vitro with or without TRH antibody to assess the direct influence of prostatic TRH on thyroid hormone secretion. Total thyroxine (T4) and triiodothyronine (T3) were increased significantly in the culture media of ventral prostate, anterior pituitary and thyroid gland when compared with thyroid gland plus anterior pituitary culture media. However, media T4 and T3 concentration decreased significantly in thyroid gland alone; also in thyroid gland plus ventral prostate, thyroid gland plus anterior pituitary and thyroid gland plus anterior pituitary plus ventral prostate were co-cultured with TRH antibody (Ab) in a dose dependent manner. The results suggest that ventral prostatic TRH is one of the stimulating factors of thyroid hormone secretion under these in vitro conditions.
General Background on the Hypothalamic-Pituitary-Thyroid (HPT) Axis
Published in Critical Reviews in Toxicology, 2007
R. Thomas Zoeller, Shirlee W. Tan, Rochelle W. Tyl
This article reviews the thyroid system, mainly from a mammalian standpoint. However, the thyroid system is highly conserved among vertebrate species, so the general information on thyroid hormone production and feedback through the hypothalamic-pituitary-thyroid (HPT) axis should be considered for all vertebrates, while species-specific differences are highlighted in the individual articles. This background article begins by outlining the HPT axis with its components and functions. For example, it describes the thyroid gland, its structure and development, how thyroid hormones are synthesized and regulated, the role of iodine in thyroid hormone synthesis, and finally how the thyroid hormones are released from the thyroid gland. It then progresses to detail areas within the thyroid system where disruption could occur or is already known to occur. It describes how thyroid hormone is transported in the serum and into the tissues on a cellular level, and how thyroid hormone is metabolized. There is an in-depth description of the alpha and beta thyroid hormone receptors and their functions, including how they are regulated, and what has been learned from the receptor knockout mouse models. The nongenomic actions of thyroid hormone are also described, such as in glucose uptake, mitochondrial effects, and its role in actin polymerization and vesicular recycling. The article discusses the concept of compensation within the HPT axis and how this fits into the paradigms that exist in thyroid toxicology/endocrinology. There is a section on thyroid hormone and its role in mammalian development: specifically, how it affects brain development when there is disruption to the maternal, the fetal, the newborn (congenital), or the infant thyroid system. Thyroid function during pregnancy is critical to normal development of the fetus, and several spontaneous mutant mouse lines are described that provide research tools to understand the mechanisms of thyroid hormone during mammalian brain development. Overall this article provides a basic understanding of the thyroid system and its components. The complexity of the thyroid system is clearly demonstrated, as are new areas of research on thyroid hormone physiology and thyroid hormone action developing within the field of thyroid endocrinology. This review provides the background necessary to review the current assays and endpoints described in the following articles for rodents, fishes, amphibians, and birds.
Thyroid insufficiency during pregnancy: complications and implications for screening
Published in Expert Review of Endocrinology & Metabolism, 2008
In 2007, clinical practice guidelines concerning the management of thyroid dysfunction during pregnancy and postpartum were published in the Journal of Clinical Endocrinology and Metabolism. They were elaborated on by a panel of experts, representative of the Latin American Thyroid Society, the Asia and Oceania Thyroid Society, the American Thyroid Association, the European Thyroid Association, the American Association of Clinical Endocrinologists and the Endocrine Society. In women not known to have thyroid dysfunction, universal screening during pregnancy is not recommended, but thyroid function tests are advised in those with prior therapeutic head or neck irradiation, a history of preterm delivery, in cases of infertility and in the presence of risk factors for thyroid disease. Risks factors for thyroid dysfunction are considered as a personal or family history of thyroid diseases, presence of thyroid antibodies (when known), personal history of autoimmune diseases and the presence of signs or symptoms suggesting hypo- or hyperthyroidism. In this review, we summarize the modifications of the pituitary–thyroid axis during pregnancy, with particular attention on thyroid insufficiency. We consider the most important risk factors for thyroid dysfunction and focus our attention on the complications for the progeny, deriving from a condition of maternal thyroid impairment. We will discuss the matters in favor of or against a thyroid-screening program at the beginning of pregnancy.