Can hypothyroidism cause hypothermia, particularly in older adults or individuals with severe hypothyroidism?

Can Hypothyroidism Cause Hypothermia?

Yes, hypothyroidism can cause hypothermia, particularly in severe cases progressing to myxedema coma, where hypothermia is a cardinal clinical feature and life-threatening emergency requiring immediate intensive care treatment. 1, 2, 3

Mechanism of Hypothermia in Hypothyroidism

Thyroid hormones are essential for maintaining normal body temperature through several mechanisms:

• Thyroid hormones markedly increase the basal metabolic rate and enhance the number and activity of mitochondria in almost all cells of the body, which is critical for heat generation. 4
• In severe hypothyroidism, the profound reduction in metabolic activity leads to decreased heat production, making patients unable to maintain normal core body temperature. 4, 1
• The metabolic slowing affects oxygen consumption by tissues and reduces the synthesis and utilization of high-energy phosphates, further compromising thermogenesis. 4

Clinical Presentation: Myxedema Coma

Myxedema coma represents the most extreme manifestation of severe hypothyroidism and is characterized by the triad of altered mental status, hypothermia, and multiple organ system dysfunction. 2, 3

Key features include:

• Hypothermia is one of the defining clinical features of myxedema coma, along with cardiovascular depression, respiratory depression, gastrointestinal slowing, impaired diuresis, and central nervous system depression. 4, 3
• This condition carries a mortality rate of up to 30% even with treatment, making early recognition critical. 1
• The very young, the very old, and people with impaired temperature perception and regulation are at increased risk of hypothermia. 5

Precipitating Factors

Myxedema coma typically occurs in patients with longstanding, poorly controlled hypothyroidism when exposed to acute stressors:

• Surgery, trauma, infection, cold exposure, and myocardial infarction can precipitate myxedema coma in patients with severe hypothyroidism. 6, 2
• Hypoglycemia must be identified and corrected immediately as it can also trigger decompensation. 6

Diagnostic Considerations

The diagnosis of myxedema coma is based on clinical presentation—history and physical findings—not on any objective thyroid laboratory test alone. 3

Important diagnostic points:

• Patients typically present with rectal temperatures well below normal (e.g., 29.5°C/85.1°F has been reported). 7
• Untreated hypothyroidism can progress to severe hypothyroidism with decompensation (myxedema coma), which requires treatment in an intensive care unit. 1
• The combination of altered mental status, hypothermia, and bradycardia in an elderly patient should immediately raise suspicion for myxedema coma. 2, 3

Critical Management Principles

Treatment with thyroid hormone replacement should be initiated upon suspicion of myxedema coma even prior to obtaining laboratory confirmation, given the high mortality rate. 2

Essential treatment components:

• The American College of Physicians recommends immediate hospitalization in an intensive care unit for aggressive supportive care, maintaining airway, breathing, and circulation with intubation and ventilation if necessary (Glasgow Coma Score ≤8). 8
• Glucocorticoid administration (hydrocortisone 100 mg IV every 8 hours) is recommended until adrenal insufficiency is ruled out, as thyroid hormone replacement can precipitate adrenal crisis. 8, 4
• Concomitant use of thyroid hormone and artificial rewarming is contraindicated—external heat causes peripheral vasodilation that further decreases circulation to vital organs and increases shock. 4
• Administration of thyroid hormones will restore normal body temperature in 24 to 48 hours if heat loss is prevented by keeping the patient covered with blankets in a warm room. 4

Important Caveats

Hypothermia in a patient with elevated TSH does not automatically indicate myxedema coma—accidental environmental hypothermia can transiently elevate TSH as an adaptive response. 7

• In one reported case, an elderly man with accidental hypothermia (rectal temperature 29.5°C) had elevated TSH (28.3 mU/L) that normalized exponentially after body temperature was restored, without thyroid hormone treatment. 7
• This adaptive elevation of TSH upon accidental hypothermia should be borne in mind, and TSH should be rechecked after normalization of body temperature before diagnosing primary hypothyroidism. 7

The key distinction is clinical context: myxedema coma patients have longstanding severe hypothyroidism with multi-organ dysfunction, whereas accidental hypothermia patients have primary environmental cold exposure with secondary TSH elevation that resolves with rewarming alone. 7, 3