Thyroid storm or crisis is a life-threatening condition characterized by an exaggeration of the manifestations of thyrotoxicosis. When thyroid storm was first described, the acute mortality rate was nearly 100%. Today, the prognosis is significantly improved if appropriate therapy is initiated early; however, the mortality rate continues to be approximately 20%.

Thyroid storm usually occurs in patients who have unrecognized or inadequately treated thyrotoxicosis and a superimposed precipitating event, such as thyroid surgery, nonthyroid surgery, infection, or trauma.

Fever (> 102° F) is the cardinal manifestation. Tachycardia is usually present, and tachypnea is common, but the blood pressure is variable. Cardiac arrhythmias, congestive heart failure, and ischemic heart symptoms may develop. Nausea, vomiting, diarrhea, and abdominal pain are frequent features (Fig. 38-1). Central nervous system manifestations include hyperkinesis, psychosis, and coma. A goiter is a helpful finding but is not always present.

Serum thyroxine (total T₄ and free T₄) and triiodothyronine (total T₃ and free T₃) are usually significantly elevated, and serum thyroid-stimulating hormone (TSH) is undetectable. These hormone levels, however, cannot reliably distinguish patients with thyroid storm from those who have uncomplicated thyrotoxicosis. Other common findings include anemia, leukocytosis, hyperglycemia, azotemia, hypercalcemia, and elevated liver enzymes.

The diagnosis must be made on the basis of suspicious but nonspecific clinical findings. If the diagnosis is strongly suspected, waiting for the results of tests may cause a critical delay in the initiation of effective lifesaving therapy. Clinical features are therefore the key. Table 38-1 provides a useful scoring system to aid in diagnosis.

Similar presentations may be seen with sepsis, pheochromocytoma, and malignant hyperthermia.

The immediate goals are to decrease thyroid hormone synthesis, to inhibit thyroid hormone release, to reduce the heart rate, to support the circulation, and to treat the precipitating condition. Because beta₁-adrenergic receptors are significantly increased in patients with this condition, beta₁-selective blockers are the preferred agents for heart rate control.

 Propylthiouracil, 600 to 1200 mg daily (oral, rectal, or nasogastric [NG] tube)

 Methimazole, 60 to 120 mg daily (oral, rectal, NG tube, or intravenous [IV])

 Sodium iodide (NaI), 1 g over 24 hours (IV)

 Potassium iodide (SSKI), 5 drops every 6 to 8 hours (oral)

 Lugol solution, 10 drops every 6 to 8 hours (oral)

 Esmolol, 500 mg over 1 minute, followed by 50 to 300 mg/kg/minute infusion (IV)

 Metoprolol, 5 to 10 mg every 2 to 4 hours (IV)

 Diltiazem, 60 to 90 mg every 6 to 8 hours orally, or 0.25 mg/kg over 2 minutes, followed by infusion of 10 mg/minute (IV)

 Intravenous fluids

 Stress glucocorticoid doses (hydrocortisone, methylprednisolone, dexamethasone)

 Identification and treatment of the underlying cause of thyroid storm

Plasma exchange and plasmapheresis can be lifesaving measures in patients with thyroid storm who have not adequately responded to the foregoing standard measures.

Myxedema coma is a life-threatening condition characterized by an exaggeration of the manifestations of hypothyroidism. Myxedema coma originally had a mortality rate of 100%. Today, the outlook is much improved for appropriately treated patients; the mortality rate in more recent studies has varied from 0% to 45%.

Myxedema coma usually occurs in older patients who have inadequately treated or untreated hypothyroidism and a superimposed precipitating event. Important events include prolonged cold exposure, infection, trauma, surgery, myocardial infarction, congestive heart failure, pulmonary embolism, stroke, respiratory failure, gastrointestinal bleeding, and administration of various drugs, particularly those with a depressive effect on the central nervous system.

Hypothermia, bradycardia, and hypoventilation are common. Blood pressure, although generally reduced, is more variable. Pericardial, pleural, and peritoneal effusions are often found. Ileus is frequently present, and acute urinary retention may be seen. Central nervous system manifestations include seizures, stupor, and coma (Fig. 38-2). Deep tendon reflexes are absent or exhibit a delayed relaxation phase. Typical hypothyroid skin and hair changes are often apparent. A goiter, although frequently absent, is a helpful finding. A thyroidectomy scar may also be an important clue.

Serum T₄ (total and free T₄) and T₃ (total and free T₃) levels are usually low, and TSH is significantly elevated. Other frequent abnormalities include anemia, hyponatremia, hypoglycemia, and elevated serum levels of cholesterol and creatine kinase (CK). Arterial blood gases often reveal carbon dioxide retention and hypoxemia. The electrocardiogram often shows sinus bradycardia, various types and degrees of heart block, low voltage, and T-wave flattening.

The diagnosis must be made on clinical grounds on the basis of the findings described earlier. Serum levels of thyroid hormones are reduced and the TSH level is elevated, but the delay involved in waiting for test results may unnecessarily postpone the initiation of effective therapy.

The goals are to replace the depleted thyroid hormone pool rapidly, to replace glucocorticoids, to support vital functions, and to treat any precipitating conditions. The normal total body pool of T₄ is about 1000 μg (500 μg in the thyroid, 500 μg in the rest of the body).

Levothyroxine (LT₄), liothyronine (LT₃), or both may be used. The best regimen remains undetermined, but the combination of LT₄ plus LT₃ is recommended. Regimens for LT₄ alone, LT₃ followed by LT₄, and LT₄ plus LT₃ are as follows:

 Oxygen

 IV fluids

 Mechanical ventilation (if necessary)

 Rewarming (blankets or central rewarming)

 Stress glucocorticoid doses (hydrocortisone, methylprednisolone, dexamethasone)

 Identification and treatment of the underlying cause of myxedema coma