Thyroid Disorders in the ICU
Alan P. Farwell
I. THYROID STORM
A. General principles.
1. Thyroid storm is a rare, life-threatening complication of thyrotoxicosis in which a severe form of the disease is usually precipitated by an intercurrent medical problem.
2. Thyroid storm is primarily a clinical diagnosis, as there are no absolute levels of elevated thyroid hormones that are diagnostic of storm.
3. Thyroid storm is a medical emergency that should be managed in the ICU.
B. Etiology.
1. Hyperthyroidism is the most common cause of thyrotoxicosis leading to thyroid storm.
2. Precipitating factors associated with thyroid storm include infections, stress, trauma, thyroidal or nonthyroidal surgery, diabetic ketoacidosis, labor, heart disease, iodinated contrast studies, thyroid hormone overdose, and radioiodine treatment (especially if there was no pretreatment with antithyroid drugs).
3. Historically, thyroid storm was frequently associated with surgery for hyperthyroidism, but this is rarely seen now.
C. Pathophysiology.
1. Thyroid storm is the most severe manifestation of thyrotoxicosis, and the onset is rapid.
2. Increased levels of T4 and T3 are necessary, but there is no absolute level that establishes the diagnosis.
3. While the cause of the rapid clinical decompensation is unknown, a sudden inhibition of thyroid hormone binding to plasma proteins by the precipitating factor, causing a rise in free hormone concentrations in the already elevated free hormone pool, may play a role in the pathogenesis of thyroid storm.
D. Diagnosis.
1. Symptoms.
a. Thyroid storm is primarily a clinical diagnosis, with features similar to those of thyrotoxicosis, but more exaggerated (Table 84-1).
b. Cardinal features include fever (temperature usually >38.5°C), tachycardia out of proportion to the fever, and mental status changes.
TABLE 84-1 Clinical Features of Thyroid Storm | |
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c. Tachyarrhythmias, especially atrial fibrillation in the elderly, are common, as are nausea, vomiting, diarrhea, agitation, and delirium.
d. Coma and death may ensue in up to 20% of patients, frequently due to cardiac arrhythmias, congestive heart failure (CHF), hyperthermia, or the precipitating illness.
2. Signs.
a. Most patients display the classic signs of Graves disease, including ophthalmopathy and a diffusely enlarged goiter, although thyroid storm has been associated with toxic nodular goiters.
b. In the elderly, severe myopathy, profound weight loss, apathy, and a minimally enlarged goiter may be observed.
c. There are no distinct laboratory abnormalities, and thyroid hormone levels are similar to those found in uncomplicated thyrotoxicosis; there is little correlation between the degree of elevation of thyroid hormones and the presentation of thyroid storm.
3. Differential diagnosis.
a. The differential diagnosis of thyroid storm includes sepsis, neuroleptic malignant syndrome, malignant hyperthermia, and acute mania with lethal catatonia, all of which can precipitate thyroid storm in the appropriate setting.
b. Clues to the diagnosis of thyroid storm are a history of thyroid disease, history of iodine ingestion, and the presence of a goiter or stigmata of Graves disease.
c. Burch and Wartofsky have published a scoring system for the diagnosis of thyroid storm (Table 84-2). The diagnosis of thyroid storm was possible with a score of 25 to 45 and is likely with a score >45. Thyroid storm is unlikely with a score <25.
TABLE 84-2 Clinical Scoring System for the Diagnosis of Thyroid Storm (Burch and Wartofsky) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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d. A recent study suggested new criteria for the rapid diagnosis of thyroid storm.
i. Patients who had specific CNS manifestations (restlessness, delirium, psychosis/mental aberrations, somnolence/lethargy, convulsions) needed to have only one of four additional conditions: temperature
of 38°C or higher; tachycardia of 130 beats per minute or higher; class IV CHF; or gastrointestinal/hepatic manifestations (diarrhea, nausea/vomiting, or a bilirubin above 3 mg/dL).
of 38°C or higher; tachycardia of 130 beats per minute or higher; class IV CHF; or gastrointestinal/hepatic manifestations (diarrhea, nausea/vomiting, or a bilirubin above 3 mg/dL).
ii. Those without CNS mainfestations needed three out of four conditions: temperature of 38°C or higher; tachycardia of 130 beats per minute or higher; class IV CHF; or gastrointestinal (GI)/hepatic manifestations (diarrhea, nausea/vomiting, or a bilirubin above 3 mg/dL).
e. In any event, the physician must have a high clinical index of suspicion for thyroid storm, as therapy must be instituted before the return of thyroid function tests in most cases.
E. Treatment.
1. Thyroid storm is a major medical emergency that must be treated in an ICU (Table 84-3).
2. Treatment includes supportive measures such as intravenous fluids, antipyretics, cooling blankets, and sedation.
3. β-Adrenergic blockers or calcium channel blockers are given to control tachyarrhythmias.
4. Antithyroid drugs are given in large doses, with propylthiouracil (PTU) being preferred over methimazole due to its additional advantage of impairing peripheral conversion of T4 to T3.
5. PTU and methimazole can be administered by nasogastric tube or rectally if necessary; neither of these preparations is available for parenteral administration.
6. Iodides, orally or intravenously, may be used only after antithyroid drugs have been administered, although the useful radiographic contrast dye iopanoic acid is no longer available in the United States.
7. High-dose dexamethasone is recommended as supportive therapy, as an inhibitor of T4-to-T3 conversion and as management of possible intercurrent adrenal insufficiency.
8. Orally administered ion-exchange resins (colestipol or cholestyramine) can trap hormone in the intestine and prevent recirculation, and plasmapheresis has also been used in severe cases.
9. Treatment of the underlying precipitating illness is essential to survival in thyroid storm.
10. Once stabilized, the antithyroid treatment should be continued until euthyroidism is achieved, at which point a final decision regarding antithyroid drugs, surgery, or 131Iodine (131I) therapy can be made.
F. Complications.
1. The mortality rate of thyroid storm has been reported to be 10% to 20%.
2. Complications of thyroid storm other than mortality are the same as complications from the underlying etiology of the thyrotoxicosis (i.e., opthalmopathy in Graves disease).
3. After definitive therapy for hyperthyroidism (surgery or radioactive iodine), hypothyroidism is the most common, and desired, result.
TABLE 84-3 Treatment of Thyroid Storm | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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II. MYXEDEMA COMA
A. General principles.
1. Myxedema coma is a rare syndrome that represents the extreme expression of severe, long-standing hypothyroidism.
2. Even with early diagnosis and treatment, the mortality can be as high as 60%.
3. Myxedema coma occurs most often in the elderly and during the late fall and winter months.
4. Myxedema coma is primarily a clinical diagnosis, as there are no absolute levels of decreased thyroid hormones that are diagnostic.
5. Myxedema coma is a medical emergency that should be managed in the ICU.
B. Etiology.
1. Hypothyroidism by any cause can be the underlying cause of myxedema coma.
2. Most episoides of myxedema coma are caused by a precipitating factor in the setting of severe hypothyroidism.
3. Common precipitating factors include pulmonary infections, cerebrovascular accidents, trauma, surgery, and CHF.
4. The clinical course of lethargy proceeding to stupor and then coma is often hastened by drugs, especially sedatives, narcotics, antidepressants, and tranquilizers, especially in the undiagnosed hypothyroid patient who has been hospitalized for other medical problems.
C. Pathophysiology.
1. Myxedma coma is the most severe manifestation of hypothyroidsm.
2. Decreased levels of T4 and T3 and increases in thyroid-stimulating hormone (TSH) are necessary, but there is no absolute level upon which the diagnosis is clear.
D. Diagnosis.
1. Symptoms.
a. Cardinal features of myxedema coma are hypothermia, respiratory depression, hypotension, and unconsciousness (Table 84-4).
b. Most patients have the physical features of severe hypothyroidism, including bradycardia; macroglossia; delayed reflexes; and dry, rough skin and myxedematous facies, which result from the periorbital edema, pallor, hypercarotinemia, periorbital edema, and patchy hair loss.
c. Hypotonia of the gastrointestinal tract is common and often so severe as to suggest an obstructive lesion.
d. Urinary retention due to a hypotonic bladder is related but less frequent.
TABLE 84-4 Clinical Features of Myxedema Coma | ||
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2. Signs.
