Commonest cause of hypothyroidism is

(Thyroid dysgenesis) (1872-73-Nelson 17th) (481-Ghai 7th)HYPOTHYROIDISM results from deficient production of thyroid hormone or a defect in thyroid hormone or a defect in thyroid hormonal receptor activity* Someform of thyroid dysgenesis (aplasia, hypoplasia or an ectopic gland) is the most common cause of congenital hypothyroidism, accounting for 85% of cases, 10% are caused by an in bom error of thyroxine synthjesis and 5% are the result of transplacental maternal thyrotropin receptor blocking antibody.* Pendred syndrome - congenital hypothyroidism with sensorineural deafness and goiter, also have a positive perchlorate discharge.* ** Sodium L-thyroxine given orally is the treatment of choices (side effects are - craniosynostosis and temperature problems pseudotumour cerebri)* Acquired hypothyroidism - is most commonly caused by auto immune destruction of thyroid as a part of Chronic lymphocytic thyroidits (Hashimoto's thyroiditis