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Hyperthyroidism is diagnosed when the free T4 is elevated. If TSH is low and the free T4 is normal, the free T3 should be checked since there is an uncommon form of hyperthyroidism called “T3 thyrotoxicosis” that is due to a selective increase in T3. Causes for hyperthyroidism include:
Graves’ disease appears to be caused by TSH like antibodies produced by an autoimmune disorder. These TSH like antibodies bind the TSH receptors to continuously activate them. These auto antibodies have been referred to by a number of names including TSI (thyroid stimulating immunoglobulin) and LATS (long acting thyroid stimulator). The diagnosis of Graves’ disease or Plummer’s disease is made by finding a suppressed TSH, an elevated free T4 or free T3, and a radioactive iodine uptake scan to indicate the presence of a diffuse goiter (Graves’), a solitary hot nodule (Plummer’s) or a hot nodule in a multinodular goiter (Plummer’s). The radioactive iodine uptake scan is important to rule out a “cold” nodule. If a “cold” solitary nodule is identified (does not take up radioactive iodine on scan) there is a 10-15% chance of malignancy (cancer) and further evaluation is required. A thyroid nodule in a multinodular goiter without a history of high risk factors for cancer is not usually an indication for further evaluation since it has the same risk of cancer as a normal thyroid gland. High risk factors for thyroid cancer are:
The clinical appearance of hyperthyroidism includes
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