What is the characteristic feature of Hashimoto's thyroiditis?

Hashimoto's thyroiditis is primarily characterized by autoimmune destruction of the thyroid gland. This condition occurs when the body's immune system mistakenly attacks the thyroid tissue, leading to chronic inflammation and dysfunction of the gland. The destruction is mediated by the presence of antibodies against various thyroid antigens, such as thyroglobulin and thyroid peroxidase.

As a result of this autoimmune attack, patients typically experience hypothyroidism, as the thyroid is unable to produce sufficient amounts of thyroid hormones. The condition can also lead to the gradual replacement of thyroid tissue with fibrous tissue, further impairing thyroid function.

In the context of the provided choices, hyperactivity of the thyroid gland, excessive production of thyroid hormones, and the presence of thyroid nodules are not characteristic features of Hashimoto's thyroiditis. Instead, the hallmark of this disease lies in the autoimmune process that leads to thyroid gland destruction.