The final member of the thyroiditis quartet is lymphocytic thyroiditis (also called silent thyroiditis). This type of thyroiditis is characterized histologically by – you guessed it – a ton of lymphocytes (as in the image above). Just lymphocytes. No germinal centers, plasma cells, or Hurthle cells (like you see in Hashimoto thyroiditis).

The pathogenesis of lymphocytic thyroiditis is unresolved. There may be an inherited component (there is a high frequency of both HLA-DR3 and HLA-DR5 in patients with this type of thyroiditis) and/or an autoimmune component (patients often make anti-thyroglobulin and anti-peroxidase antibodies).

Whatever the pathogenesis is, the disorder itself is mild. Some patients are asymptomatic (hence the name “silent”); others present with a painless, slightly enlarged thyroid. Mild, transient hyperthyroidism may develop over the first few weeks after onset, but by two months, the disease has usually run its course.