Hashimoto's thyroiditis

Hashimoto's thyroiditis is a type of autoimmune inflammation of the thyroid gland with goitre, resulting in hypothyroidism.

The goitre in Hashimoto's thyroiditis varies from small to large and is usually firm and painless, often with an irregular, bosselated surface. Pain may rarely occur in an uncomplicated Hashimoto's goitre, but if associated with an enlarging thyroid this symptom suggests the emergence of a B-cell lymphoma, an uncommon thyroid malignancy found almost exclusively in patients with long-standing Hashimoto's thyroiditis.

As thyroid destruction occurs progressively over months to years, patients are often euthyroid at presentation. However, serum thyroid-stimulating hormone (TSH) levels can be elevated even if thyroid hormones are within the reference range, representing subclinical thyroid failure with pituitary-driven compensation.

The prevalence of autoimmune hypothyroidism in the general Caucasian population is 1-2% in women and 0.1-0.2% in men, whereas thyroid autoantibodies can be found in 20% of middle-aged women, reflecting the presence of focal thyroiditis. Only a fraction of individuals with serological evidence of thyroid autoimmunity therefore have clinical disease.