Which histologic findings are characteristic of subacute granulomatous thyroiditis?

Updated: Mar 23, 2021
  • Author: Stephanie L Lee, MD, PhD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Answer

The thyroid gland is moderately enlarged (unilaterally or bilaterally) and edematous in de Quervain thyroiditis, and the gland’s capsule is intact. Affected areas are firm and yellow-white; they stand out from the normal thyroid substance, which is brown and has a more rubbery consistency.

Microscopic

The changes are patchy and vary with the stage of the disease. The early phase is the active inflammatory phase and is characterized by areas of entirely disrupted follicles, which are replaced by neutrophils, forming microabscesses.

In a later phase, the classic changes of granulomatous thyroiditis develop. This is characterized by aggregations of lymphocytes, large histiocytes, and plasma cells among damaged thyroid follicles. Multinucleated giant cells enclose pools or fragments of colloid, from which stems the designation giant cell thyroiditis. Colloid is also found within the giant cells, following a process called colloidophagy.

In the final stages, the areas of injury are replaced by a chronic, inflammatory infiltrate and fibrosis. Different histologic stages sometimes are found in the same gland, suggesting waves of destruction over a period of time.

Under a scanning electron microscope, the cytomorphology of subacute granulomatous thyroiditis shows loss of a uniform honeycomb cellular arrangement, variation in size and decreased or shortened microvilli in follicular cells, and the appearance of round or ovoid giant cells.

The giant cells are closely associated with the granulomas; the small lymphocytes in the granulomas are CD3+, CD8+, and CD45RO+ cytotoxic T cells.

In the nongranulomatous lesions, the follicles are infiltrated by CD8+ T lymphocytes, plasmacytoid monocytes, and histiocytes, resulting in disrupted basement membrane and rupture of the follicles. These findings suggest that cellular immune response may play an important role in the pathogenesis of subacute thyroiditis.


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