Key clinical features supporting a diagnosis of Hashimoto's thyroiditis in adults include symptoms of hypothyroidism such as fatigue, weight gain, cold intolerance, constipation, dry skin, and depression, although symptoms may be subtle or absent initially NICE NG145. Physical examination may reveal a diffusely enlarged, firm, and non-tender thyroid gland (goitre) NICE NG145. There may also be a history of other autoimmune diseases or family history of thyroid autoimmunity Ragusa et al. 2019.
Laboratory findings that support the diagnosis include elevated thyroid-stimulating hormone (TSH) levels with low or normal free thyroxine (FT4), consistent with hypothyroidism or subclinical hypothyroidism NICE NG145. The hallmark laboratory feature is the presence of thyroid peroxidase antibodies (TPOAbs), which are elevated in most cases and indicate autoimmune thyroid destruction NICE NG145. Testing for TPOAbs is recommended in adults with elevated TSH to confirm autoimmune thyroiditis NICE NG145. Thyroglobulin antibodies may also be present but are less specific Ragusa et al. 2019.
Ultrasound imaging, while not diagnostic alone, typically shows a diffusely hypoechoic and heterogeneous thyroid gland with reduced vascularity, supporting the diagnosis in conjunction with clinical and serological findings NICE NG145.
In summary, the diagnosis of Hashimoto's thyroiditis in adults is supported by clinical features of hypothyroidism or goitre, elevated TSH, positive TPOAbs, and characteristic ultrasound findings NICE NG145; these are consistent with the autoimmune pathogenesis described in recent literature Ragusa et al. 2019.