Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis and Hashimoto's disease, is an autoimmune disease in which the thyroid gland is gradually destroyed. Early on there may be no symptoms. Over time the thyroid may enlarge forming a painless goiter. Some people eventually develop hypothyroidism with its accompanying weight gain, feeling tired, constipation, depression, and general pains. After many years the thyroid typically shrinks in size. Potential complications include thyroid lymphoma1.
It is difficult to reliably sonographically differentiate Hashimoto thyroiditis from other thyroid pathology.
Ultrasound features can be variable depending on the severity and phase of disease2,6:
- Diffusely enlarged thyroid gland with a heterogeneous echotexture is a common sonographic presentation7.
- The presence of hypoechoic micronodules (1-6mm) with surrounding echogenic septations is also considered to have a relatively high positive predictive value4,5. This appearance may be described as pseudonodular or a giraffe pattern.
- Colour Doppler study usually shows normal or decreased flow, but occasionally there might be hypervascularity similar to a thyroid inferno.
- Prominent reactive cervical nodes may be present, especially in level VI, but they have normal morphologic features.
- Patients are at higher risk for papillary thyroid carcinoma, so a discrete nodule should be considered for biopsy.
In some situations, large nodules may be present, which may be referred to as nodular Hashimoto thyroiditis8.
Overt, symptomatic thyroid dysfunction is the most common complication, with about 5% of persons with subclinical hypothyroidism and chronic autoimmune thyroiditis progressing to thyroid failure every year. Transient periods of thyrotoxicosis (over-activity of the thyroid) sometimes occur, and rarely the illness may progress to full hyperthyroid Graves' disease with active orbitopathy (bulging, inflamed eyes). Rare cases of fibrous autoimmune thyroiditis present with severe dyspnea (shortness of breath) and dysphagia (difficulty swallowing), resembling aggressive thyroid tumors – but such symptoms always improve with surgery or corticosteroid therapy. Primary thyroid B cell lymphoma affects fewer than one in a thousand persons, and it is more likely to affect those with long-standing autoimmune thyroiditis9.