3
Determination of Etiology
Table 1. Causes of Thyrotoxicosis
Thyrotoxicosis associated with a normal or elevated radioactive iodine (RAI)
uptake over the neck
a
GD
TA or TMNG
Trophoblastic disease
yroid-stimulating hormone (TSH)-producing pituitary adenomas
Resistance to thyroid hormone (T
3
receptor β mutation [THRB])
b
Thyrotoxicosis associated with a near-absent RAI uptake over the neck
Painless (silent) thyroiditis
Amiodarone-induced thyroiditis
Subacute (granulomatous, de Quervain's) thyroiditis
Palpation thyroiditis
Iatrogenic thyrotoxicosis
Factitious ingestion of thyroid hormone
Struma ovarii
Acute thyroiditis
Extensive metastases from follicular thyroid cancer
a
In iodine-induced or iodine-exposed hyperthyroidism (including amiodarone type 1), the uptake
may be low.
b
Patients are not uniformly clinically hyperthyroid.
Determination of Etiology
1. The etiology of thyrotoxicosis should be determined. If the
diagnosis is not apparent based on the clinical presentation and
initial biochemical evaluation, diagnostic testing is indicated and
can include, depending on available expertise and resources: (S-M)
1. measurement of thyrotropin receptor antibodies (TRAb)
2. determination of the radioactive iodine uptake (RAIU) or
3. measurement of thyroidal blood flow on ultrasonography.
• An
123
I or
99m
Tc pertechnetate scan should be obtained when the clinical
presentation suggests a toxic adenoma or toxic multinodular goiter.
