Thyroid storm, treatment

Peripheral Antagonists. The relatively long duration of action of the thyroid hormones makes it desirable to have compounds capable of blocking them competitively at their site of action. This is desirable in the treatment of thyroid storm where the reduction of circulating hormone levels brought about by the inhibition of their synthesis is too slow. 

III.b.1.4. lodinated contrast media. When iodides or thioamides are contraindicated, the contrast media ipodate and iopanoic acid may be used to treat hyperthyroidism. These drugs rapidly inhibit conversion of T4 to T3 in the liver, kidney, brain and pituitary gland, and the effects are so rapid that they are sometimes helpful in the treatment of thyroid storm (see below). The drugs are non toxic and have prolonged effect. Precautions are similar to iodide,... 

Occasionally patients develop a dramatically acute and severe form of thyrotoxicosis which may be life-threatening, termed thyroid crisis or thyroid storm. In this condition the patient is at risk of cardiac complications, notably arrhythmia and ventricular failure, and it requires very urgent treatment. It is essential to use high doses of anti-thyroid drugs, and PTU is often preferred for this, particularly because of its fast absorption. Iodides or ipodate are often... 

The most serious complication of hyperthyroidism is thyroid storm (thyrotoxic crisis). This is an acute exacerbation of hyperthyroidism with marked tachycardia, fever, mental status changes and haemodynamic collapse. It is usually precipitated by acute illness, trauma, parturition or surgery, especially of the thyroid gland. The mortality rate is 20-30%, even with aggressive treatment, due to cardiac failure, arrhythmias or hyperthermia. 

The imidazoles methimazole [60-56-0] (MMI) (12) and Carbimazole [22232-54-8] (13) act by inhibiting intrathyroidal hormone synthesis, whereas the thiouracils (10) [51-52-5] and (11) [56-04-2] also inhibit the peripheral deiodination of T4 to T3. Thus, the latter are preferred in the treatment of thyroid storm (thyrotoxic crisis) where a quick drop in circulating T3 is desired (2,9). In general, the imidazoles are 10 times as active as the thiouracils. 

Propylthiouracil differs from other members of the group in that it also inhibits peripheral conversion of T to Tj, but only at the high doses used in treatment of thyroid storm (p. 705). 

In hyperthyroidism the beneficial effects of a single dose may be felt in one month, and patients should be reviewed at 6 weeks to monitor for onset of hypothyroidism. The maximal effect of radioiodine may take 3 months. P-adrenoceptor blockade and, in severe cases, an antithyroid drug (but see footnote 1) will be needed to render the patient comfortable whilst waiting this is more likely when radioiodine is used for treatment of patients with relapsing thyrotoxicosis. Very rarely radiation thyroiditis causes excessive release of hormone and thyroid storm. Repeated doses are sometimes needed. 

In addition to blocking hormone synthesis, propylthiouracil also inhibits the peripheral deiodi-nation of T to Tji this added effect provides a rationale for the choice of propylthiouracil over methimazole in the treatment of severe hyperthyroid states such as thyroid storm. 

The direct and immediate treatment result, as opposed to the delayed effect of radioiodine, is another advantage of surgery. The latter may be particularly relevant to patients who require rapid correction of thyrotoxicosis in case of thyroid storm or severe iodine-induced hyperthyroidism. 

In patients with a poor or delayed response to antithyroid drugs, in elderly patients, pregnant women, or in patients with neurologic symptoms of thyrotoxicosis (incipient thyroid storm), early thyroidectomy is the treatment of choice, especially in IIH and when high-dose thionamides, glucocorticoids and intensive care fail to improve the patients conditions within 24h. Thyrotoxic crisis occurs in about 1% of all patients admitted to hospitals for hyperthyroidism Schaaiet al., 1990). 

The ability of PTU to inhibit the enzyme 5 -D-l (i.e., the peripheral deiodination of T4 to T3, in addition to its intrathyroidal inhibition of thyroid hormone formation) has made PTU the drug of choice in the emergency treatment of thyroid storm (68). Single doses of PTU in excess of 300 mg are capable of almost total blockage of peripheral T3 production (69). 

Iodides have. several poorly understood actions on the thyroid. They inhibit organitication and hormone release. In addition, iodide de-crca.scs the size and vascularity of the hyperplastic gland, effects which are useful in the preparation of patients for thyroidectomy. In phamia-cological dose.s. the main effect of iodides is to inhibit hnmtone release (possibly by inhibition of thywglobulin proteolysis) and. because thyrotoxic symptoms are reduced relatively quickly (2 7 days), iodine is valuable in the treatment of thyrotoxic crisis ( thyroid storm —a life-threatening acute exacerbation of all the symptoms of thyrotoxicosis). Iodine caimoi be used for the long-term treatment of hyperthyroidism because its antithyroid action tends to diminish. 

The following therapeutic measures should be instituted promptly (1) suppression of thyroid hormone formation and secretion (2) antiadrenergic therapy (3) administration of corticosteroids and (4) treatment of associated complications or coexisting factors that may have precipitated the storm (Table 20-2). 

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