Hashimoto thyroiditis is a type of autoimmune inflammation of the thyroid gland with goiter, resulting in hypothyroidism.
The goiter 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 Hashimotos goiter, 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, but serum thyroid stimulating hormone (TSH) levels can be elevated even if thyroid hormones are within the reference range, representing sublinical thyroid failure with pituitary-driven compensation.
The prevalenve 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. Thus only a fraction of individuals with serological evidence of thyroid autoimmunity have clinical disease.