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Dr. Prakash Kumar Prusty* Original Research Paper Diabetology Original Research Paper Volume - 11 | Issue - 01 | January - 2021 | PRINT ISSN No. 2249 - 555X | DOI : 10.36106/ijar Diabetology UNDERACTIVE THYROID AND L-THYROXINE Dr. Prakash MBBS, MD (Med), FIDM (Diabetology) Consultant Diabetologist - Department Of Kumar Prusty* Endocrinology S.C.B Medical College, Cuttack.*Corresponding Author KEYWORDS : Thyroid gland and the thyroid hormones Various causes of primary hypothyroidism are tabulated in Table 1. The thyroid gland produces hormones that serve essential and critical Iodine is an essential component of the thyroid hormone. Iodine functions in the body related to metabolism and energy utilization, deciency can result in goiter, thyroid nodules, and hypothyroidism. maturation of the central nervous system, thermostatic control of body The most severe consequence of iodine deciency is cretinism that temperature, overall growth, bone development, and various other results in restricted mental and physical development in utero and 1 metabolic processes in the body . Triiodothyronine (T3), during childhood. Iodine fortication programs are one of the safest tetraiodothyronine (Thyroxine, T4), and calcitonin are the hormones and cheapest public health interventions for the prevention of secreted by the thyroid gland. However, T3 and T4 are considered as cognitive and physical impairment 9. Despite such efforts, suboptimal the proper thyroid hormones, secreted by the follicular epithelial cells iodine status still affects large parts of underdeveloped and developing involving trace element, Iodine as the essential building block for both 2 counties, as well as specic subpopulations in several developed of them . The functioning of the thyroid gland is governed by the countries—most notably, pregnant women. anterior pituitary gland, and hypothalamus thus constituting a self- 3 regulatory loop, termed a hypothalamic-pituitary-thyroid axis . In iodine-sufcient areas, the most common cause of hypothyroidism Thyrotropin-releasing hormone (TRH) released by the hypothalamus is chronic autoimmune thyroiditis called Hashimoto's disease. High into the hypothalamic-hypophyseal portal system of the anterior concentrations of anti-thyroid antibodies mainly thyroid peroxidase pituitary gland, stimulates thyrotropin cells of the anterior pituitary to antibodies and anti-thyroglobulin antibodies are present in most secrete thyroid-stimulating hormone (TSH). TSH released into the 10 patients with autoimmune thyroiditis . Primary hypothyroidism is blood circulation binds to the Gs-protein coupled TSH-receptors on diagnosed based on clinical symptoms like mental slowing, the basolateral aspect of the thyroid follicular cell leading to the depression, dementia, weight gain, constipation, dry skin, hair loss, activation of adenylyl cyclase and intracellular levels of cAMP. The elevated levels of cAMP, in turn, activates protein kinase A and causes cold intolerance, vocal changes, irregular menstruation, infertility, phosphorylation of various proteins to modify their functions. The muscle stiffness and muscle ache, bradycardia, and hypercholestero- thyroid hormone binds to the intranuclear receptors in virtually every lemia. However, it is always conrmed with serum tests. organ system in the body, including the heart, central nervous system, autonomic nervous system, bones, and gastrointestinal tract, wherein, Ÿ Secondary hypothyroidism- It is a pituitary gland disorder causing it activates the genes for increasing metabolic rate and thermogenesis decreased TSH release, thus decreased levels of T3 and T4. leading to increased consumption of oxygen and energy. Ÿ Tertiary hypothyroidism- It is caused by a hypothalamic disorder Hypothyroidism (Underactive thyroid) that results in decreased TRH levels, leading to decreased TSH, and corresponding T3 and T4 levels. Usually, secondary and tertiary Hypothyroidism is a common condition of insufciency of thyroid 11 hormones namely T3 and T44 . The normal value of levels of serum hypothyroidism are collectively termed as central hypothyroidism . thyroid hormones are as follows5 : Central hypothyroidism is rare and affects both sexes equally. It is Ÿ T4: 4.8 to 13.2 mg/dL more often associated with the pituitary than hypothalamic disorders 1 2 Ÿ Free T4: 0.9 to 2 ng/dL but frequently involves both . The diagnosis of central Ÿ T3: 80 to 220 ng/dL hypothyroidism involves testing of levels of free T4 rather than TSH. Ÿ TSH: 0.35 to 5.50 mIU/mL TRH stimulation test analyzing the delayed TSH response to TRH also supports the diagnosis. Various etiological factors responsible for It is a common condition and is more prevalent in women, the elderly, central hypothyroidism are tabulated in Table 1. and certain ethnic groups6 . Hypothyroidism is more common in 4,13 patients with autoimmune diseases, such as type 1 diabetes, Table 1. Causes of different types of hypothyroidism autoimmune gastric atrophy, and coeliac disease, and can occur as part Causative factor Examples of causative factors of multiple autoimmune endocrinopathies. Individuals with Downs' Primary hypothyroidism syndrome or Turners' syndrome have an increased risk of hypothyroidism. The symptoms of deciency are diverse that can be Iodine Either severe iodine deciency or excess iodine readily diagnosed and effectively managed with medications. in the body However, if untreated may lead to hypertension, dyslipidemia, Autoimmune Chronic autoimmune thyroiditis called infertility, cognitive impairment, and neuromuscular dysfunction and diseases Hashimoto's thyroiditis and atrophic thyroiditis may become potentially fatal in severe cases. The simplest way of Drugs Amiodarone, lithium, tyrosine kinase inhibitors, classication of hypothyroidism to understand the dysfunctional gland IFN-α, IL-2 thalidomide, monoclonal antibodies in the hypothalamic-pituitary-thyroid axis is as follows: like ipilimumab and nivolumab, antiepileptics Ÿ Primary hypothyroidism- Decreased secretion of thyroid like valproic acid, and antitubercular drugs used hormones by the thyroid gland causes a compensatory increase of as a second-line of therapy for MDR-TB TSH by the feedback mechanism. Therefore, the serum TSH level is used to screen for primary hypothyroidism in most patients. Primary Iatrogenic Radioiodine (I131) treatment for Graves' disease hypothyroidism is further classied as7 treatment or toxic nodular disease, hemithyroidectomy, o Clinical / Overt- It shows raised levels of serum TSH and reduced radiotherapy, or surgery in the treatment of head levels of T4. and neck cancer o Subclinical- It shows raised levels of serum TSH, however, T4 is Transient Destructive thyroiditis, post-partum, silent normal and there are no symptoms of thyroid dysfunction. It is thyroiditis thyroiditis, a viral infection like De Quervain's also termed compensated hypothyroidism or mild hypothyroidism. syndrome Autoimmunity is the commonest cause of subclinical hypothyroidism 8. This condition is more prevalent in about 10% Thyroid gland Mycoplasma infections, thyroid malignancy, of women of perimenopausal age. inltration lymphoma, sarcoidosis, Riedel's thyroiditis INDIAN JOURNAL OF APPLIED RESEARCH 35 Volume - 11 | Issue - 01 | January - 2021 | PRINT ISSN No. 2249 - 555X | DOI : 10.36106/ijar Genetic Autoimmunity related genes like HLA class I are non-specic, and are fewer and less classic signs and symptoms region, PTPN22, SH2B3, and VAV3), general than observed younger individuals. Hypothyroidism has clinical and thyroid-specic genes like FOXE1, ATXN2, implications related to nearly all major organs (Figure 1), but the and PDE8B cardiovascular system is the most studied. Hypothyroidism results in Central hypothyroidism increased vascular resistance, decreased cardiac output, decreased left Pituitary tumors Secreting non-secreting tumors as in pituitary ventricular function, and changes in several markers of cardiovascular adenoma, Metastatic pituitary lesions contractility. Extra-pituitary Primary intracranial craniopharyngioma, factors meningioma, germinoma In general, the clinical manifestations of hypothyroidism range from no signs or symptoms-to-life threatening like Myxedema coma. It was Pituitary Sheehan's syndrome rst described in the late 1900s as an outcome of long-standing dysfunction untreated and severe hypothyroidism, which is a rare condition. Hypothalamic Post-pituitary surgery, Post-external radiation Myxedema coma leads to an altered mental status, hypothermia, dysfunction therapy progressive lethargy, and bradycardia and can eventually result in Drugs Dopamine, somatostatins, glucocorticosteroids, multiple organ dysfunction syndrome and death 17 . Therefore, early bexarotene, retinoid X receptor-selective ligands, recognition of the disease and initiation of thyroid hormone therapy salicylates, and drugs interfering with the neuro- and other supportive measures. Although very rare, severe primary dopaminergic system and dopamine hypothyroidism can lead to pituitary hyperplasia with concomitant Hormonal Resistance to TSH or TRH pituitary pathologies like secondary adrenal insufciency and resistance symptoms like amenorrhea. Concerning laboratory ndings in various Increased TSH Leptin stimulation types of hypothyroidism, levels of various thyroid hormones are Genetic Pituitary-specic transcription factor defects summarized in table 2. such as PIT-1, PROP-1 LHX3 or HESX1, Table 2. Levels of various thyroid hormones in different types of Isolated TRH deciency, Mutations in the TSH- 5 (beta) subunit gene, inactivating mutation in hypothyroidism
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