<prompt> Which of the following is true regarding thyrotoxicosis?In Graves disease, antibodies are formed to TSH receptors, which result in excessive thyroxine secretionHashimotos thyroiditis occur in young malesIn primary hypothyroidism, decreased TSH levels are seenAll of the above  <response>: Pathophysiology of Graves thyrotoxicosisThe thyrotoxicosis results from the production of immunoglobulin G IgG antibodies directed against the TSH receptor on the thyroid follicular cell, which stimulate thyroid hormone production and proliferation of follicular cells, leading to goitre in the majority of patients. These antibodies are termed thyroid-stimulating immunoglobulins or TSH receptor antibodies TRAb and can be detected in the serum of 8095 of patients with Graves disease. The concentration of TRAb in the serum is presumed to fluctuate to account for the natural history of Graves thyrotoxicosis. Thyroid failure seen in some patients may result from the presence of blocking antibodies against the TSH receptor, and from tissue destruction by cytotoxic antibodies and cell-mediated immunity.Hashimotos thyroiditis is characterised by destructive lymphoid infiltration of the thyroid, ultimately leading to a varying degree of fibrosis and thyroid enlargement. Hashimotos thyroiditis increases in incidence with age and affects approximately 3.5 per 1000 women and 0.8 per 1000 men each year.In the vast majority of cases, hypothyroidism results from an intrinsic disorder of the thyroid gland primary hypothyroidism. In this situation, serum T 4 is low and TSH is elevated, usually in excess of 20 mIUL. Measurements of serum T 3 are unhelpful since they do not discriminate reliably between euthyroidism and hypothyroidism.Reference: : Davidson P R I N C I P L E S and Practice O F M E D I C I N E 23rd edition page no 643,646, 640 