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Understand Thyroid – A Functional Myriad, and Clear Skepticism on Hypothyroidism

Dr. K. V. Narasimha Raju & Dr. B. Swapna

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Hypothyroidism
Hypothyroidism is a condition characterized by abnormally low thyroid hormone production. Because thyroid hormone affects growth, development, and many cellular processes, inadequate thyroid hormone has widespread consequences for the body. It is estimated that 3% to 5% of the population has some form of hypothyroidism. The condition is more common in women than in men, and its incidence increases with age.

Causes
Hypothyroidism is caused by any structural or functional derangement that interferes with the production of adequate levels of thyroid hormone.

Iodine deficiency remains the most common cause of hypothyroidism worldwide. In areas of iodine sufficiency, autoimmune disease (Hashimoto’s thyroiditis) and iatrogenic causes are most common. Here is the list of etiologies:

Primary:

  • Autoimmune hypothyroidism: Hashimoto’s thyroiditis, atrophic thyroiditis
  • Iatrogenic: I131 treatment, subtotal or total thyroidectomy, external irradiation of neck for lymphoma or cancer
  • Drugs: iodine excess (including iodine-containing contrast media and amiodarone), lithium, antithyroid drugs, p-aminosalicyclic acid, interferon-á and other cytokines, aminoglutethimide
  • Congenital hypothyroidism: absent or ectopic thyroid gland, dyshormonogenesis, TSH-R mutation
  • Iodine deficiency
  • Infiltrative disorders: amyloidosis, sarcoidosis, hemochromatosis, scleroderma, cystinosis, Riedel’s thyroiditis
  • Overexpression of type 3 deoiodinase in infantile hemangioma

Transient:

  • Silent thyroiditis, including postpartum thyroiditis
  • Subacute thyroiditis
  • Withdrawal of thyroxine treatment in individuals with an intact thyroid
  • After I131 treatment or subtotal thyroidectomy for Graves’ disease

Secondary:

  • Hypopituitarism: tumors, pituitary surgery or irradiation, infiltrative disorders, Sheehan’s syndrome, trauma, genetic forms of combined pituitary hormone deficiencies
  • Isolated TSH deficiency or inactivity
  • Bexarotene treatment
  • Hypothalamic disease: tumors, trauma, infiltrative disorders, idiopathic
Important and common conditions of hypothyroidism

Thyroid Goiter: Caused by Dietary Iodide Deficiency

Endemic Colloid Goiter. The term “goiter” means a greatly enlarged thyroid gland. Lack of adequate iodine in the diet leads to the development of extremely large thyroid glands, called Endemic Goiters. The mechanism for development oflarge endemic goiters is the following:

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