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 (diffuse goiter),
- Plummer’s disease (nodular goiter, generally seen in postmenopausal women), and
- a pituitary TSH secreting tumor, which is a rare cause of hyperthyroidism (both the TSH and free T4 are elevated)
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:
- a history of irradiation to the head and neck (1 out of 9 with this history develop thyroid cancer)
- a rapidly growing or hard nodule
- palpable regional lymph nodes
- vocal cord paralysis
The clinical appearance of hyperthyroidism includes
- exophthalmos (bulging of the eyes) and pretibial myxedema (in Graves’)
- nervousness and tremor
- heat intolerance (always feeling hotter than those around you and intolerant of heated environments)
- sweating with moist warm skin
- palpitations and possible tachycardia