Endocrinology · Hypothyroidism
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Myxedema coma is a life-threatening decompensation of severe, long-standing hypothyroidism often precipitated by infection, cold exposure, or sedative use.
The classic clinical presentation includes altered mental status, hypothermia, hypoventilation, and bradycardia.
Physical examination frequently reveals non-pitting edema (myxedema), delayed relaxation of deep tendon reflexes, and macroglossia.
Laboratory findings typically demonstrate elevated TSH and low free T4 in primary hypothyroidism, alongside hyponatremia and hypoglycemia.
The diagnosis is clinical and must be made immediately without waiting for laboratory confirmation, as mortality remains high.
Initial management requires intravenous levothyroxine (T4) and intravenous liothyronine (T3) alongside stress-dose glucocorticoids to prevent adrenal crisis.
Passive rewarming is indicated for hypothermia, but aggressive active rewarming should be avoided to prevent vasodilation and circulatory collapse.
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A 72-year-old female is brought to the emergency department by her daughter due to increasing lethargy. The patient has a history of Hashimoto thyroiditis but has been non-compliant with her medications for several months. On examination, she is obtunded, her temperature is 94.1°F (34.5°C), heart rate is 48 bpm, and respiratory rate is 8 breaths/min. Physical exam reveals periorbital edema, thickened skin on the lower extremities, and delayed relaxation phase of the ankle jerks. Laboratory studies show a serum sodium of 126 mEq/L and a TSH of 98 mIU/L.
What is the most appropriate next step in the management of this patient?
Intravenous levothyroxine and stress-dose glucocorticoids
The patient presents with classic signs of myxedema coma; immediate treatment with thyroid hormone replacement and glucocorticoids is required to prevent adrenal insufficiency and death.
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Etiology / Epidemiology
Severe, decompensated hypothyroidism in elderly women. Triggered by infection, cold exposure, or non-compliance.
Clinical Manifestations
Altered mental status, hypothermia, and non-pitting edema. Look for bradycardia and hypoventilation.
Diagnosis
Clinical diagnosis supported by TSH and Free T4. Expect elevated TSH and low Free T4.
Treatment
Immediate IV Levothyroxine and IV Hydrocortisone. Do not delay treatment for labs.
Prognosis
High mortality rate of 30-60%. Requires ICU admission and aggressive supportive care.
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Epidemiology & Etiology
Occurs primarily in elderly women with long-standing, undiagnosed, or undertreated hypothyroidism. Precipitating factors include infection, trauma, surgery, or sedative use. Cold weather exposure is a classic environmental trigger for this metabolic crisis.
Pertinent Anatomy
The hypothalamic-pituitary-thyroid axis is disrupted, leading to systemic failure. The myxedema results from glycosaminoglycan deposition in the interstitial space, causing characteristic non-pitting edema.
Pathophysiology
Severe thyroid hormone deficiency leads to decreased metabolic rate and multi-organ failure. The body fails to maintain core temperature, resulting in profound hypothermia. Reduced sympathetic tone causes bradycardia and decreased cardiac output, while respiratory drive is blunted, leading to hypercapnia.
Clinical Manifestations
Patients present with altered mental status ranging from lethargy to coma. Classic signs include non-pitting edema, hypothermia, and hypoventilation. Red flags include hypotension, bradycardia, and hyponatremia due to impaired free water clearance.
Diagnosis
Diagnosis is clinical; do not wait for lab results to initiate therapy. Order TSH and Free T4 to confirm primary hypothyroidism. Expect elevated TSH and low Free T4. Check serum cortisol to rule out concomitant adrenal insufficiency.
Treatment
Initiate IV Levothyroxine (T4) immediately. Administer IV Hydrocortisone prior to thyroid replacement to prevent adrenal crisis if secondary adrenal insufficiency is present. Provide passive rewarming and mechanical ventilation as needed. Avoid aggressive fluid resuscitation due to risk of heart failure.
Prognosis
Mortality remains high at 30-60% despite treatment. Survivors require ICU admission for continuous cardiac monitoring and serial assessment of mental status.
Differential Diagnosis
Sepsis: fever present vs. hypothermia in myxedema
Adrenal Crisis: hyperpigmentation and hypotension
Hypoglycemia: rapid reversal with dextrose
Drug Overdose: history of ingestion/tox screen
Stroke: focal neurological deficits present