Thyrotoxicosis without hyperthyroidism

Iodine excess (including radiocontrast, amiodarone) Thyrotoxicosis without hyperthyroidism Subacute thyroiditis Silent (painless) thyroiditis... 

The common causes of thyrotoxicosis are shown in Table 41-6.29,30 Thyrotoxicosis can be related to the presence or absence of excess hormone production (hyperthyroidism). Graves disease is the most common cause of hyperthyroidism. Thyrotoxicosis in the elderly is more likely due to toxic thyroid nodules or multinodular goiter than to Graves disease. Excessive intake of thyroid hormone may be due to overtreatment with prescribed therapy. Surreptitious use of thyroid hormones also may occur, especially in health professionals or as a self-remedy for obesity. Thyroid hormones can be obtained easily without a prescription from health food stores or Internet sources. 

Beta blockers without intrinsic sympathomimetic activity (eg, metoprolol, propranolol, atenolol) are effective therapeutic adjuncts in the management of thyrotoxicosis since many of these symptoms mimic those associated with sympathetic stimulation. Propranolol has been the 3 blocker most widely studied and used in the therapy of thyrotoxicosis. Beta blockers cause clinical improvement of hyperthyroid symptoms but do not typically alter thyroid hormone levels. Propranolol at doses greater than 160 mg/d may also reduce T3 levels approximately 20% by inhibiting the peripheral conversion of T4 to T3. 

From a practical standpoint, the measurement of iodine content is of interest in hyperthyroid patients without radioactive uptake. A value above 30 mg, excludes a subacute thyroiditis and suggests an iodine induced thyrotoxicosis (Fig. 13). 

Figure 13 Interest of measurement of iodine content in hyperthyroidism with radioactive uptake (GR 49 Grave diseases) or without radioactive uptake (I.I.T. 28 iodine induced thyrotoxicosis S.T. 15 subacute thyroiditis)...

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