eMedicine Specialties > Emergency Medicine > Endocrine & Metabolic

Hypothyroidism and Myxedema Coma

Author: Erik D Schraga, MD, Consulting Staff, Department of Emergency Medicine, Mills-Peninsula Emergency Medical Associates; Consulting Staff, Permanente Medical Group, Kaiser Permanente, Santa Clara Medical Center
Contributor Information and Disclosures

Updated: Mar 13, 2008

Introduction

Background

Hypothyroidism is a clinical syndrome in which the deficiency or absence of thyroid hormone slows bodily metabolic processes. Symptoms can manifest in all organ systems and range in severity based on the degree of hormone deficiency. The disease typically progresses over months to years but can occur quickly following cessation of thyroid replacement medication or surgical removal of the thyroid gland.

The term myxedema refers to the thickened, nonpitting edematous changes to the soft tissues of patients in a markedly hypothyroid state. Myxedema coma, a rare, life-threatening condition, occurs late in the progression of hypothyroidism. The condition is seen typically in elderly women and is often precipitated by infection, medication, environmental exposure, or other metabolic-related stresses. Since rapid confirmatory laboratory tests are often unavailable, the diagnosis may be made on clinical grounds with treatment started promptly.

Treatment of myxedema coma requires potentially toxic doses of thyroid hormone, and mortality rates exceeding 20% have been reported even with optimum therapy.

For more information, see Medscape's Hypothyroidism Resource Center.

Pathophysiology

Thyroid hormone is secreted in response to stimulation of the thyroid gland by thyroid-stimulating hormone (TSH) from the anterior pituitary gland. TSH is released through the action of thyrotropin-releasing hormone (TRH) from the hypothalamus.

Hypothyroidism can be caused by permanent loss or atrophy of functional thyroid tissue (primary hypothyroidism), insufficient stimulation of a normal thyroid gland by as a result of hypothalamic or pituitary disease (secondary hypothyroidism, often accompanied by compensatory thyroid gland enlargement), or a defect in the TSH molecule (control hypothyroidism).

Primary hypothyroidism accounts for approximately 90-95% of hypothyroidism, with a predominantly autoimmune-mediated etiology. TSH hypersecretion produces excessive thyroid tissue, resulting in goiter formation. Surgical and radiation ablation account for a large percentage of acquired cases of hypothyroidism. Congenital abnormalities, malignancies, and infiltrative disorders including amyloidosis and sarcoidosis can also lead to the disease. Iodine deficiency is rarely responsible for hypothyroidism in developed countries; however, it remains the primary cause worldwide.

Suprathyroidal disorders including hypopituitarism and hypothalamic lesions account for fewer than 10% of cases. Rarely, peripheral resistance to thyroid hormone may occur.

The congenital absence or deficiency of thyroid tissue may result in cretinism, a neurodevelopmental disorder characterized by lethargy, poor peripheral circulation, constipation, and goiter. Since infants are asymptomatic, neonatal screening is vital to prevent permanent sequelae.

Frequency

United States

Reports on screening surveys for thyroid disease show an incidence of 5.8% for subclinical thyroid abnormalities. However, those with overt signs and symptoms of hypothyroidism likely make up fewer than 2% of women and 0.2% of men.

Myxedema coma occurs rarely, appearing in 0.1% of all cases of hypothyroidism.

International

Neonatal screening programs for congenital hypothyroidism show that in many areas around the world hypothyroidism appears in 1 of every 4000 newborns.

In developed countries, the incidence of subclinical hypothyroidism is approximately 8% in women and 3% in men. Endemic goiter usually occurs in environmentally iodine-deficient areas; throughout the world, goiter is estimated to affect 200 million people. Goiter is most common in mountainous areas of the Alps, Himalayas, and Andes, possibly due to low soil iodine content as a result of leaching away of minerals as glaciers melt.

Mortality/Morbidity

Mortality rate in myxedema coma has historically been as high as 80%. More recent data suggest that aggressive management and early recognition have improved the mortality rate to 15-20%.

Race

Anecdotal reports indicate the disease appears more often in Caucasian and Hispanic populations.

Sex

Incidence is greater in females than males (female-to-male ratio 5-10:1).

Age

The incidence of primary hypothyroidism increases progressively with age, typically at 40-50 years.

• After age 60 years, the prevalence of hypothyroidism may be as high as 8-10% in women.

Clinical

History

The symptoms characteristic of hypothyroidism are numerous yet often vague and subtle, especially in early stages of the disease.

• Lethargy
• Generalized weakness
• Brittle or thinning hair
• Menstrual irregularity
• Menorrhagia
• Forgetfulness
• Fullness in throat
• Deep, husky voice secondary to mucopolysaccharide infiltration of the vocal cords
• Cold intolerance
• Weight gain
• Muscle/joint pain or weakness
• Inability to concentrate
• Headaches
• Constipation
• Emotional lability
• Depression
• Blurred vision
• Dry hair

Physical

• Pseudomyotonic reflexes - Prolonged relaxation phase, usually at least twice as long as the contraction phase
• Hypothermia (especially in myxedema coma)
• Skin changes - Dry, cool, coarse, and thickened with a yellowish appearance
• Subcutaneous tissues - Nonpitting, waxy, dry edema, secondary to accumulation of polysaccharides
• Loss of axillary and pubic hair
• Pallor
• Loss of outer one third of eyebrows
• Abdominal distention
• Goiter
• Unsteady gait/ataxia
• Pericardial effusion
• Dull facial expression
• Coarsening or huskiness of voice
• Periorbital edema
• Bradycardia, narrow pulse pressure
• Macroglossia
• Thyroidectomy scar - In patients with altered mental status, suggests myxedema coma as a potential cause

Causes

The most common etiology of hypothyroidism worldwide is iodine deficiency as associated with endemic goiter. Conversely, a study among Chinese patients also demonstrated a significant increase in overt hypothyroidism in those with an excessive intake of iodine.¹ Within the United States and developed nations, the major causes of hypothyroidism are autoimmune destruction of the thyroid gland (eg, Hashimoto thyroiditis) and iatrogenic secondary to the treatment of Graves disease (surgical or radioactive iodine ablation of the thyroid gland). Primary hypothyroidism (dysfunction of the thyroid gland) accounts for up to 90-95% of cases. Secondary hypothyroidism (dysfunction of the pituitary or hypothalamus) accounts for the majority of the remainder of cases. ED management rarely requires distinguishing between primary and secondary origins.

• Primary causes include autoimmune, idiopathic, postoperative, and congenital etiologies; radiation; radioiodine therapy; iodine deficiency; metabolic disorders; and medications (eg, lithium, amiodarone, phenytoin, carbamazepine, iodides). Furthermore, those with underlying autoimmune thyroiditis are susceptible to disease progression while taking these medications.
• Secondary causes include pituitary and hypothalamic disorders such as trauma, neoplasm, irradiation, and infiltrative diseases including sarcoidosis or amyloidosis.
• In a patient with underlying hypothyroidism, inciting factors responsible for developing myxedema coma are numerous and include infection, trauma, cold exposure, or medications such as sedatives and anesthetics.

• Search for CME/CE on This Topic »

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• Thyroid Problems Symptoms
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• Myxedema Coma Overview
• Thyroid Problems Treatment