- Thyrotoxicosis is the clinical syndrome that results when tissues are exposed to high levels of circulating thyroid hormones. It results in a generalized acceleration of metabolic processes.
- Hyperthyroidism: hyperactivity of the thyroid gland.
Table 1. Conditions Associated with Thyrotoxicosis.

1. Diffuse toxic goiter (Graves’ disease)
2. Toxic adenoma (Plummer’s disease)
3. Toxic multinodular goiter
4. Subacute thyroiditis
5. "Silent" thyroiditis
6. Thyrotoxicosis factitia
7. Rare forms of thyrotoxicosis: ovarian struma, metastatic thyroid carcinoma (follicular), hydatidiform mole, "hamburger thyrotoxicosis," TSH-secreting pituitary tumor, pituitary resistance to T3 and T4.

Clinical Findings:
• Symptoms include heat intolerance, weight loss, weakness, palpitations, oligomenorrhea, and anxiety.
• Signs include brisk tendon reflexes, fine tremor, proximal weakness, stare, and eyelid lag. Cardiac abnormalities may be prominent, including sinus tachycardia, atrial fibrillation, and exacerbation of coronary artery disease or heart failure.
• In the elderly, hyperthyroidism may present with only atrial fibrillation, heart failure, weakness, or weight loss, and a high index of suspicion is needed to make the diagnosis.
Diagnosis
• Hyperthyroidism should be suspected in any patient with compatible symptoms, as it is a readily treatable disorder that may become very debilitating.
• Plasma TSH is the best initial diagnostic test, as a TSH level >0.1 microunits/mL excludes clinical hyperthyroidism. If plasma TSH is <0.1 microunits/mL, plasma free T4 should be measured to determine the severity of hyperthyroidism and as a baseline for therapy. If plasma free T4 is elevated, the diagnosis of clinical hyperthyroidism is established.
- If plasma TSH is < 0.1 microunits/mL but free T4 is normal, the patient may have clinical hyperthyroidism due to elevation of plasma T3 alone; therefore, plasma T3 should be measured in this case.
-Very mild (or subclinical) hyperthyroidism may suppress TSH to <0.1 microunits/mL, and therefore suppression of TSH alone does not confirm that symptoms are due to hyperthyroidism.
- TSH may also be suppressed by severe nonthyroidal illness (see Evaluation of Thyroid Function). A third-generation TSH assay with a detection limit of 0.02 microunits/mL may be helpful in patients with suppressed TSH and nonthyroidal illness. Most patients with clinical hyperthyroidism have plasma TSH levels that are <0.02 microunits/mL in such assays, whereas nonthyroidal illness rarely suppresses TSH to this degree.2
TREATMENT
- Symptomatic therapy: ß adrenergic antagonist, Verapamil.
- Definitive therapy: radioactive Iodine (RAI), thionamides and subtotal thyroidectomy.The choice of therapy varies with the nature and severity of the illness and prevailing customs.

Receptors: Thyroid hormone receptor - wikipedia