Hashimoto thyroiditis, also known as lymphocytic thyroiditis or chronic autoimmune thyroiditis, is a subtype of autoimmune thyroiditis. It is one of the most common thyroid disorders.
Typically affects middle-aged females (30-50 year age group with an F:M ratio of 10-15:1).
Patients usually present with hypothyroidism +/- goiter. However, a very small proportion of cases (~5%) can present with hyperthyroidism (also known as Hashitoxicosis). There is often a gradual painless enlargement of the thyroid gland during the initial phase with atrophy and fibrosis later on in the course.
The Hashitoxicosis phase, if present, usually only lasts 1-2 months. Although rare cases last much longer .
There is autoimmunity to the thyroid gland which bears both humoral- and cell-mediated features. This is followed by lymphocytic infiltration of the thyroid gland with lymphoid follicles replacing thyroid follicles. This may affect the thyroid gland in either a diffuse or focal manner. Cell populations include:
- lymphocytic aggregates
- transformed follicular cells (Askanazy/oxyphilic/Hurthle cells)
Later stages show superadded fibrosis.
- antithyroglobulin antibodies: found in ~70% of cases
- thyroid peroxidase antibodies (TPO): found in 90-95% of cases
- Turner syndrome
- primary thyroid lymphoma
- Hashimoto encephalopathy (rare)
- Down syndrome
- other autoimmune disorders
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 disease :
- diffusely enlarged thyroid gland with a heterogeneous echotexture is a common sonographic presentation (especially initial phase)
- the presence of hypoechoic micronodules (1-6 mm) with surrounding echogenic septations is also considered to have a relatively high positive predictive value ; this appearance may be described as pseudonodular or a giraffe pattern.
- color Doppler study usually shows normal or decreased flow, but occasionally there might be hypervascularity similar to a thyroid inferno
- the hypervascularity does not reflect thyrotoxicosis, indeed it appears to be more common in hypothyroid Hashimoto patients !
- 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 thyroiditis .
- early stages: may show increased uptake
- late stages: single or multiple areas of reduced uptake (cold spots)
- diffuse high uptake throughout the thyroid is consistent with chronic thyroiditis (or a normal variant)
- superimposed focal high uptake should raise concern for a thyroid nodule including the possibility of carcinoma
History and etymology
It was first described in 1912 by Hakaru Hashimoto (1881-1934), a Japanese physician while working in Germany; in his original description, he called it 'struma lymphomatosa' .
For ultrasound appearances consider: