Severe Hyperthyroidism

Marjorie S. Safran

Patients with thyrotoxicosis rarely need hospitalization. However, some patients with severe thyrotoxicosis develop a decompensated clinical presentation called thyroid storm. It is characterized by hyperpyrexia, tachycardia, and delirium [1] and generally occurs in a patient with severe thyrotoxicosis who then experiences a stressful event. The cause of this rapid decompensation is unknown, but it may be partly due to a sudden inhibition in thyroid hormone binding to plasma proteins, resulting in a rise in the already elevated free hormone pool [2]. Thyroid storm accounts for no more than 2% of hospital admissions for all forms and complications of thyrotoxicosis, and the diagnosis is often difficult to make because there is a fine line between severe thyrotoxicosis and thyroid storm. Even when properly treated, thyroid storm has a mortality rate of 7% to 30% [3].

Etiology

Before the preoperative use of iodides and the antithyroid drugs propylthiouracil (PTU) and methimazole (MMI; Tapazole), thyroid storm was most frequently seen during and after subtotal thyroidectomy. Because these agents are used to restore euthyroidism before surgery, thyroid storm is rarely seen in this context. Thyroid storm now occurs most commonly in patients with severe underlying thyrotoxicosis, frequently undiagnosed, who become ill for other reasons, such as infections, trauma, labor, diabetic ketoacidosis, or pulmonary and cardiovascular disorders. It can occur during or after nonthyroid surgery, and has been reported after external beam radiation to the neck [4], ingestion of sympathomimetic drugs (such as
pseudoephedrine) in a thyrotoxic patient [5], and rarely with intentional or accidental overdoses [6,7]. Thyroid storm may rarely occur approximately 10 to 14 days after the administration of large doses of iodine 131 in patients with large goiters who have not been adequately pretreated with PTU or MMI to deplete the gland of stored thyroxine (T₄) and triiodothyronine (T₃) [8]. Beta-blockers are used to decrease symptoms of excess thyroid hormone release, but may not prevent thyroid storm.

Clinical Manifestations

There is no absolute level of circulating thyroid hormones indicative of thyroid storm, and the diagnosis is made on a clinical basis [3]. Patients with thyroid storm are almost always febrile (temperature usually higher than 100°F) and have rapid sinus tachycardia and tachyarrhythmias (especially atrial fibrillation in elderly patients) out of proportion to the degree of fever that can frequently result in congestive heart failure. Patients are often agitated, delirious, and tremulous, with hot, flushed skin due to vasodilation. The skin may be moist or dry, depending on the state of hydration. Diarrhea occurs frequently and contributes to dehydration and hypovolemia. Vascular collapse and shock, which are poor prognostic signs, may occur in these patients. Hepatomegaly with abnormal liver enzymes and splenomegaly can be present; jaundice portends a poor prognosis.

Most patients display the classic signs of thyrotoxic Graves’ disease, including ophthalmopathy, or toxic uninodular or multinodular goiter. However, in elderly patients, apathy, severe myopathy, profound weight loss, and congestive heart failure may be the predominant findings. As thyroid storm progresses, coma, hypotension, vascular collapse, and death may ensue unless active therapy is instituted.

Diagnosis and Differential Diagnosis

The diagnosis of thyroid storm is made on clinical grounds. Thyroid function tests do not differentiate between severe thyrotoxicosis and thyroid storm. Serum T₄ concentrations are usually similar, although it has been suggested that the serum-free T₄ concentration is significantly higher in patients with thyroid storm [2], which might partially explain their more severe symptoms. On the other hand, the serum T₃ concentrations are not higher and in fact may be less elevated or even normal in these patients when the precipitating cause is an intercurrent illness or surgery because peripheral T₃ production from T₄ is markedly impaired in a wide variety of acute and chronic systemic illnesses. Liver function tests are frequently abnormal, especially in elderly patients with congestive heart failure. Elevations in total and free serum calcium concentrations may occur.

The differential diagnosis for a patient presenting with hyperpyrexia, delirium, and tachycardia includes severe infection, malignant hyperthermia [9], neuroleptic malignant syndrome, and acute mania with lethal catatonia. Thyroid storm can be distinguished from these disorders clinically by a history of thyroid disease, thyroid hormone, or iodine ingestion and the presence on physical examination of a goiter or the stigmata of Graves’ disease, including ophthalmopathy, onycholysis, and pretibial myxedema. However, any of the disorders mentioned in the differential diagnosis can coexist with thyroid storm since they may precipitate decompensation in a patient with preexisting hyperthyroidism.

Treatment

Treatment of thyroid storm is directed toward therapy of the underlying illness, supportive care, blocking peripheral effects of thyroid hormone, and inhibition of thyroid hormone synthesis and release (Table 102.1).

Underlying Illness

Nonthyroidal illness and surgery in previously undiagnosed or only partially treated patients with hyperthyroidism are the most common causes of thyroid storm. Thus, the precipitating disease should be vigorously treated. Cardiac arrhythmias and congestive heart failure require approximately twice the dose of digoxin needed in euthyroid patients, and refractory arrhythmias should alert the physician to the presence of thyrotoxicosis. Patients may also be refractory to heparin and insulin, with higher doses required. It is evident that these patients must receive adequate antibiotic therapy; careful fluid, electrolyte, and vitamin supplementation; vigorous pulmonary therapy; and careful pre- and postoperative care. If emergency surgery is required in a thyrotoxic patient, propranolol, PTU or MMI, iodides, and perhaps corticosteroids should be given before, during, and after surgery.

Supportive Care

A cooling blanket can be used if the temperature rises above 101°F, but the shivering response should be decreased by using drugs that block the central thermoregulatory centers, such as chlorpromazine or meperidine, 25 to 50 mg every 4 to 6 hours. Antipyretics other than salicylates may also be given because salicylates displace thyroid hormones from serum-binding proteins and can increase the free hormone concentrations [10]. Dehydration is frequently present and should be treated while monitoring for congestive heart failure.

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