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.
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What this article covers
- Overview
Chronic autoimmune thyroid failure: Hashimoto thyroiditis (chronic lymphocytic thyroiditis) is a T lymphocyte-mediated autoimmune disease that progressively destroys thyroid follicles, leading over months to years to hypothyroidism.
- Epidemiology
Common disease: thyroid hormone deficiency overall affects more than 10 million Americans, and Hashimoto thyroiditis accounts for most cases in iodine-sufficient regions.
- Risk factors
Family history of thyroid autoimmunity: the strongest identifiable risk factor; Hashimoto thyroiditis clusters in families.
- Pathophysiology
Lymphocytic and plasma cell infiltration: the thyroid gland is diffusely infiltrated by lymphocytes and plasma cells, forming lymphoid follicles within the gland.
- Clinical features
Painless, diffusely enlarged, non-tender goiter: the classic examination finding; the gland is typically firm but not hard, and lymphadenopathy is not expected.
- Differential diagnosis
Painless (silent) thyroiditis: also a destructive lymphocytic thyroiditis, but typically transient and self-limited rather than progressing to permanent hypothyroidism; occurs unrelated to pregnancy…
- Diagnosis
The diagnosis is established biochemically: an elevated TSH with a low free T4 defines overt hypothyroidism, while an elevated TSH with a normal free T4 defines subclinical hypothyroidism; TPO…
- Management
First, confirm overt hypothyroidism (TSH elevated, free T4 low) and start levothyroxine 1.6 mcg/kg lean body weight PO once daily in otherwise healthy adults, taken on an empty stomach 60 minutes before breakfast or coffee.
- Complications
Myxedema coma: severe, decompensated hypothyroidism with altered mental status, hypothermia, and hypoventilation, typically precipitated by infection, myocardial infarction, stroke, trauma…
- 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 for primary hypothyroidism with TSH at diagnosis and periodically thereafter, given the strong autoimmune clustering.
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- Graves disease
Graves disease is an autoimmune disorder in which thyrotropin receptor antibodies stimulate the thyroid, causing hyperthyroidism, and is the most common cause of thyrotoxicosis in iodine-sufficient regions. Diagnosis rests on a suppressed thyroid-stimulating hormone with elevated free thyroxine and positive thyrotropin receptor antibodies, and first-line treatment is a thionamide, most often methimazole, with radioactive iodine or thyroidectomy reserved for recurrence or patient preference.
- 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.
- Painless thyroiditis
Painless (silent) thyroiditis is a self-limited destructive thyroiditis, usually arising in patients with underlying autoimmune thyroid disease, that releases preformed hormone in a triphasic pattern of thyrotoxicosis, hypothyroidism, and recovery without a tender gland. Treatment is symptomatic, with a beta-blocker for the thyrotoxic phase and temporary levothyroxine for a symptomatic hypothyroid phase, because thionamides and radioactive iodine have no role.
- Thyroid nodules
A thyroid nodule is a discrete structural lesion within an otherwise normal thyroid gland, found on ultrasound in about 40% of the United States population though palpable in far fewer, and malignant in roughly 5%. Evaluation begins with a thyroid-stimulating hormone (TSH) level and thyroid ultrasonography, and management is surveillance for benign or low-risk nodules, with lobectomy or total thyroidectomy reserved for cytology suspicious for or diagnostic of malignancy.