Hashimoto thyroiditis

Hashimoto thyroiditis (also known as lymphocytic thyroiditis ¹ or chronic autoimmune thyroiditis ²) is a sub type of autoimmune thyroiditis. It is one of the commonest of all thyroid disorders.

Epidemiology

Typically affects middle aged females (30-50 year age group with a F:M ratio of ~ 10 - 15:1). 

Clinical presentation

Patients usually present with hypothyroidism +/- a goitre. However a very small proportion of cases (~5%) can present with hyperthyroidism (hashithyrotoxicosis). There is often a gradual painless enlargement of the thyroid gland during the initially phase with atrophy and fibrosis later on in the course.

Pathology

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. 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 added fibrosis.

Serological markers

• antithyroglobulin antibodies - found in 55-90% of cases ²
• thyroid peroxidase antibodies (TPO) - found in 90-95% of cases ²

Associations

• Turner syndrome
• primary thyroid lymphoma ⁶
• Hashimoto encephalopathy (rare)
• Down syndrome
• Other auto immune disorders 
  • systemic lupus erythematosus (SLE)
  • type 1 diabetes
  • rheumatoid arthritis (RA)
  • Sjogren syndrome
  • primary biliary cirrhosis

Radiographic features

Ultrasound

It is difficult to reliably sonographically differentiate Hashimoto thyroiditis from other thyroid pathology. Ultrasound features can be variable depending of the severity and phase of disease ^1,5. 

• a diffusely enlarged thyroid gland with a heterogeneous echotexture is a common sonographic presentation ⁶. 
• the presence of hypoechoic micronodules (1-6mm) with a surroundning echogenic rim is also considered to have a relatively high positive predictive value ^3-4. 

In some situations, large nodules may be present - see nodular Hashimoto thyroiditis ¹⁰.

Scintigraphy

Radioactive iodine 

• early stages - may show increased uptake 
• late stages - single or multiple areas of reduced uptake (cold spots). 

Etymology

It was first described in 1912 by Hikaru Hashimoto, Japanense physician (1881-1934) ⁷

Differential diagnosis

For ultrasound appearences consider

• lymphoma affecting thyroid gland
• papillary thyroid carcinoma
• sub acute granulomatous (de Quervain) thyroiditis