Thyrotoxicosis factitia

Excess thyroid hormone intake (thyrotoxicosis factitia)... 

Thyrotoxicosis factitia is hyperthyroidism produced by the ingestion of exogenous thyroid hormone. This may occur when thyroid hormone is used for inappropriate indications, when excessive doses are used for accepted medical indications, or when it is used surreptitiously by patients. 

Thyrotoxicosis factitia should be suspected in a thyrotoxic patient without evidence of increased hormone production, thyroidal inflammation, or ectopic thyroid tissue. The RAIU is low because thyroid gland function is suppressed by the exogenous thyroid hormone. Measurement of plasma thyroglobulin reveals the presence of very low levels. 

Serial measurement of Tg is most useful in detecting recurrence of DTC following surgical resection or radioactive iodine ablation. Tg determination is used as an adjunct to ultrasound and scanning. Assessment of serum Tg also aids in the management of infants with congenital hypothyroidism, All patients with hyperthyroidism should have elevated Tg low concentrations of Tg may be an indication that thyrotoxicosis factitia is present. 

Thyroid uptake measurements may also be of value in the diagnosis of subacute thyroiditis and thyrotoxicosis factitia. In both conditions the blocked thyroid gland syndrome may be found with high circulating levels of thyroid hormone and zero or low thyroid uptake. 

Patients are sometimes seen who are taking excessive amounts of f-thy-roxine either as thyrotoxicosis factitia (self-administered) or thyrotoxicosis medicamentosa. These should prove to be no diagnostic problem, as their tests should fall into the category of blocked thyroid syndrome, and thyroid uptake will be negligible with very high levels of thyroid hormones in the serum, particularly of total T4. 

Surreptitious ingestion of thyroid hormones may be responsible for thyrotoxicosis factitia which may be confused with other types of thyrotoxicosis associated with low radioiodine uptake. Short term... 

Mariotti S, Martino E, Cupini C, Lari R, Giani C, Baschieri L, Pinchera A. 1982. Low serum thyroglulin as a clue to the diagnosis of thyrotoxicosis factitia. New Engl J Med 307, 410-412. 

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