Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis, is a common type of autoimmune thyroid disease and the main cause of primary hypothyroidism. Often, Hashimoto's thyroiditis may present no symptoms, having hidden onset and slow development. Typical symptoms include general fatigue, throat discomfort, localized pressure, or dull pain. Hashimoto's thyroiditis can lead to damage by the autoimmune system, causing permanent hypothyroidism. Diagnosis can be facilitated through thyroid function tests, iodine-131 uptake tests, anti-thyroid antibody tests, thyroid ultrasound, and thyroid nuclear scanning.