Hypothyroidism
Hypothyroidism is thyroid hormone deficiency, most commonly caused by autoimmune (Hashimoto) thyroid failure in iodine-sufficient countries, diagnosed by an elevated thyroid-stimulating hormone with a low or normal free thyroxine. First-line treatment is levothyroxine dosed at 1.6 mcg/kg lean body weight orally once daily, titrated using thyroid-stimulating hormone rechecked no sooner than 6 weeks after any dose change.
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What this article covers
- Overview
Thyroid hormone deficiency: insufficient thyroxine (T4) and triiodothyronine (T3) production, most often from primary thyroid gland failure.
- Epidemiology
Common: affects more than 10 million people in the United States.
- Risk factors
Personal or family history of autoimmune thyroid disease: the strongest identifiable risk factor; euthyroid people with thyroid peroxidase (TPO) antibodies have a fourfold higher risk of developing hypothyroidism.
- Pathophysiology
Primary hypothyroidism reflects loss of functional thyroid tissue: from autoimmune destruction, surgical removal, radioablation, or iodine deficiency, insufficient thyroid mass fails to meet peripheral T4/T3 demand.
- Clinical features
General slowing: fatigue, weight gain despite unchanged intake, and cold intolerance are the earliest and most common complaints.
- Differential diagnosis
Hashimoto (chronic lymphocytic) thyroiditis: the most common cause; diffuse, non-tender goiter with TPO antibody positivity in about 90%, distinguished from other thyroiditis subtypes by its permanent rather than transient course.
- Diagnosis
Primary hypothyroidism is confirmed biochemically: an elevated TSH establishes thyroid hormone deficiency; a subsequently low free T4 defines overt hypothyroidism, a normal free T4 defines subclinical hypothyroidism.
- Management
First, confirm overt hypothyroidism (TSH elevated, free T4 low) and start levothyroxine at a full replacement dose of 1.6 mcg/kg lean body weight PO once daily in otherwise healthy adults, taken on…
- Complications
Myxedema coma: severe, decompensated hypothyroidism with altered mental status, hypothermia, bradycardia, hypotension, and hypoventilation, typically precipitated by infection, myocardial infarction…
- Prognosis
Excellent with adherence to replacement therapy: most patients achieve a euthyroid state and normal quality of life on levothyroxine.
- Prevention
Screen patients with type 1 diabetes mellitus at diagnosis and periodically thereafter, given the strong autoimmune clustering.
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Related articles
- Hashimoto thyroiditis
Hashimoto thyroiditis is a chronic autoimmune process in which lymphocytic infiltration destroys the thyroid, and is the most common cause of hypothyroidism in iodine-sufficient regions such as the United States. Diagnosis rests on an elevated thyroid-stimulating hormone with a low or normal free thyroxine, and first-line treatment is lifelong levothyroxine replacement dosed to normalize thyroid-stimulating hormone.
- Myxedema coma
Myxedema coma is a rare, life-threatening decompensation of severe, longstanding untreated hypothyroidism with hemodynamic compromise and mortality up to 30-40%, typically precipitated by cold exposure, infection, or another acute illness. First-line treatment is empiric intravenous glucocorticoids followed immediately by intravenous levothyroxine (300-500 mcg load, then 1.6 mcg/kg/day), with aggressive supportive care in the ICU.
- Central diabetes insipidus
Central diabetes insipidus is inability of the posterior pituitary to produce adequate antidiuretic hormone, causing free water loss, polyuria, and hypernatremia; common causes include pituitary/hypothalamic tumor, surgery, trauma, and infiltrative disease. Diagnosis is confirmed with a water deprivation test followed by a desmopressin challenge, and treatment is desmopressin (DDAVP) 10-40 mcg intranasally or 0.1-0.4 mg orally, dosed once nightly or twice daily and titrated to control polyuria while avoiding dilutional hyponatremia from over-replacement.