Hypothyroidism is caused by inadequate function of the gland itself (primary hypothyroidism), inadequate stimulation by thyroid-stimulating hormone from the pituitary gland (secondary hypothyroidism), or inadequate release of thyrotropin-releasing hormone from the brain's hypothalamus (tertiary hypothyroidism). Primary hypothyroidism is about a thousandfold more common than central hypothyroidism. Iodine deficiency is the most common cause of primary hypothyroidism and endemic goiter worldwide. In areas of the world with sufficient dietary iodine, hypothyroidism is most commonly caused by the autoimmune disease Hashimoto's thyroiditis (chronic autoimmune thyroiditis). Hashimoto's may be associated with a goiter. It is characterized by infiltration of the thyroid gland with T lymphocytes and autoantibodies against specific thyroid antigens such as thyroid peroxidase, thyroglobulin and the TSH receptor. After women give birth, about 5% develop postpartum thyroiditis which can occur up to nine months afterwards. This is characterized by a short period of hyperthyroidism followed by a period of hypothyroidism; 20–40% remain permanently hypothyroid. Autoimmune thyroiditis is associated with other immune-mediated diseases such as diabetes mellitus type 1, pernicious anemia, myasthenia gravis, celiac disease, rheumatoid arthritis and systemic lupus erythematosus. It may occur as part of autoimmune polyendocrine<unk>  (type 1 and type 2). Group Causes Primary hypothyroidism Iodine deficiency (developing countries), autoimmune thyroiditis, subacute granulomatous thyroiditis, subacute lymphocytic thyroiditis, postpartum thyroiditis, previous thyroidectomy, acute infectious thyroiditis, previous radioiodine treatment, previous external beam radiotherapy to the neckMedication: lithium-based mood stabilizers, amiodarone, interferon alpha, tyrosine kinase inhibitors such as sunitinib Central hypothyroidism Lesions compressing the pituitary (pituitary adenoma, craniopharyngioma, meningioma, glioma, Rathke's cleft cyst, metastasis, empty sella, aneurysm of the internal carotid artery), surgery or radiation to the pituitary, drugs, injury, vascular disorders (pituitary apoplexy, Sheehan<unk> , subarachnoid hemorrhage), autoimmune diseases (lymphocytic hypophysitis, polyglandular disorders), infiltrative diseases (iron overload due to hemochromatosis or thalassemia, neurosarcoidosis, Langerhans cell histiocytosis), particular inherited congenital disorders, and infections (tuberculosis, mycoses, syphilis) Congenital hypothyroidism Thyroid dysgenesis (75%), thyroid dyshormonogenesis (20%), maternal antibody or radioiodine transferSyndromes: mutations (in GNAS complex locus, PAX8, TTF-1/NKX2-1, TTF-2/FOXE1), Pendred's<unk>  (associated with sensorineural hearing loss)Transiently: due to maternal iodine deficiency or excess, anti-TSH receptor antibodies, certain congenital disorders, neonatal illnessCentral: pituitary dysfunction (idiopathic, septo-optic dysplasia, deficiency of PIT1, isolated TSH deficiency)
complications of Turner syndrome
complications of XYY syndrome
complications of Kallmann syndrome
complications of Klinefelter syndrome
onset of Kallmann syndrome
medical cause of Precocious puberty
medical cause of Hyperdontia
complications of Growth hormone deficiency