Hypothyroidism and Myxedema Coma Workup

The following measurements and studies are indicated in hypothyroidism ^[4] :

• Electrolytes

  • Hyponatremia is common secondary to extracellular volume expansion produced by elevated antidiuretic hormone.

  • Blood glucose level ranges from normal to low secondary to decreased gluconeogenesis and reduced insulin clearance.

  • Creatine phosphokinase (CPK), aspartate aminotransferase (AST) or serum glutamic oxaloacetic transaminase (SGOT), and lactate dehydrogenase (LDH) levels may be elevated in myxedema coma due to increased muscle membrane permeability. Creatine kinase (CK)-myocardial band (MB) levels are typically normal.

• Arterial blood gas (ABG): Hypoventilation commonly results in hypercapnia and hypoxia in patients with myxedema coma.

• Urinalysis: Evaluate for source of infection.

• Secondary studies

  • Thyroid function studies may not be immediately available to assist in clinical decision making in the ED.

  • Thyroid-stimulating hormone (TSH) is elevated in primary hypothyroidism, but it may be normal or low in secondary causes of hypothyroidism.

  • Free thyroxine (T4) levels are low.

  • Triiodothyronine (T3) resin uptake is decreased.

  • Free T4 index (T3 resin uptake x total serum T4) is low.

  • Critically ill patients may develop euthyroid sick syndrome, which must not be confused with a primary thyroid abnormality. These patients have low to normal TSH and T4 levels with low T3 levels.

See the list below:

• Chest radiography

  • An enlarged cardiac silhouette in a chest radiograph may suggest pericardial effusion. A chest radiograph depicting a pericardial effusion is shown in the image below.

    Pericardial effusion. Note the "water-bottle" appearance of the cardiac silhouette.

  • However, chest radiography is reported to have a 30% false-negative rate in detecting hypothyroid pericardial effusions.

  • Chest radiography can help detect pulmonary infections often associated with myxedema coma.

• Acute abdominal series: An ileus may be associated with hypothyroidism, and it may be present in myxedema coma.

• Head CT scan (noncontrast)

  • In patients with altered mental status, the scan may be helpful in ruling out other etiologies such as intracerebral hemorrhage.

  • The scan may be helpful in ruling out other etiologies of altered mental status, such as intracerebral hemorrhage.

• Echocardiography: Perform this study if pericardial effusion is suspected.

See the list below:

• Electrocardiogram

  • Bradycardia, low voltage, prolonged PR interval, T-wave abnormalities, and electrical alternans (suggestive of effusion) may be present.

• Core temperature

  • Patients with myxedema coma have a temperature below 37°C (98.6°F) in 15% of cases.

  • Fifteen percent of those patients have a temperature below 29.5°C (85°F).