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Thyrotoxicosis is a hypermetabolic clinical syndrome caused by a pathological excess of circulating free T4 (thyroxine) and/or free T3 (tri-iodothyronine).
Although commonly done, thyrotoxicosis should not be confused with, nor is it synonymous with hyperthyroidism. The latter term solely means that a patient has abnormally-elevated thyroid hormone levels, and maybe subclinical. This may in turn lead to overt symptoms and signs, which is called thyrotoxicosis.
Signs and symptoms associated with thyrotoxicosis include 1:
- nervousness, anxiety, hyperactivity
- weight loss
- muscle weakness, tremor
- increased perspiration, heat intolerance
- palpitations, tachycardia or atrial arrhythmia, systolic hypertension
- stare and eyelid retraction (i.e. proptosis)
- reduced menstrual flow
In subclinical thyrotoxicosis (normal serum free T4 and T3 with low TSH), the patient may not have any symptoms.
The signs and symptoms attributed to thyrotoxicosis stem from the acceleration of normal physiological processes as a result of excessive serum concentrations of thyroid hormones.
There are multiple causes of thyrotoxicosis 1:
- excessive exogenous thyroid hormone iatrogenesis or ingestion (e.g. hamburger thyrotoxicosis, thyrotoxicosis factitia)
- thyroiditis (where there is excessive release of stored thyroid hormone without a concomitant increase in synthesis)
- high-dose radiation therapy
- surgical manipulation
- iodinated contrast administration (see: contrast medium-induced thyrotoxicosis)
Treatment and prognosis
Upon a precipitating event, “uncomplicated” thyrotoxicosis may transform into a thyrotoxic crisis (thyroid storm) if left unmanaged.