**1. Introduction**

Thyroid gland is a butterfly shaped gland located in front of neck. Thyroid gland synthesises and secretes thyroxine under influence of thyroid stimulating hormone (TSH). Hyperproduction and secretion of thyroxine is called as hyperthyroidism and presence of excess amount of thyroxine in blood is called as thyrotoxicosis. Hence presence of thyrotoxicosis does not necessarily means presence of hyperthyroidism, as thyrotoxicosis can be due to other reasons like thyroiditis, overdose of thyroxine tablets, ectopic sources like strauma ovarii producing excess thyroxine, etc. An approach to diagnose thyrotoxicosis is shown in **Figure 1**.

**Figure 1.** *Approach to thyrotoxicosis.*

Treatment of thyrotoxicosis is symptomatic and the treatment of the cause, but treatment of hyperthyroidism is divided in three parts. First antithyroid drugs (ATD), radioactive iodine and thyroid surgery. The prevalence of hyperthyroidism is 1.2–1.6, 0.5–0.6 overt and 0.7–1.0% subclinical [1, 2]. The most frequent causes are Graves' disease (GD) and toxic nodular goitre.

#### **1.1 Prevalence**

Prevalence of thyroid disease varies with iodine sufficiency of the region The National health and nutrition examination survey (NHANES III)[3] and epidemic survey in UK [4] demonstrates female preponderance of thyroid diseases and lower incidence of hyperthyroidism with 1–2% prevalence in women and 1/10th in men.
