Rosai-Dorfman disease with thyroid involvement: a case report and literature review.

Rosai-Dorfman disease is a rare non-Langerhans cell histiocytosis that usually presents with lymph node enlargement but may involve extranodal sites. Thyroid involvement is exceedingly uncommon and often leads to diagnostic difficulties. We report the case of a 46-year-old woman with a progressively enlarging, painless cervical mass accompanied by mild fever, malaise, and difficulty swallowing. Physical examination revealed cervical lymph node enlargement and a thyroid nodule. Fine needle aspiration specimens from the thyroid gland and lymph nodes showed numerous pale histiocytes with emperipolesis, lymphocytes, neutrophils, and plasma cells. Histopathological evaluation demonstrated sinus expansion with large histiocytes exhibiting vesicular nuclei and clear cytoplasm, along with characteristic emperipolesis, while immunohistochemical staining showed strong S100 protein positivity and CD1a negativity. Treatment with oral corticosteroids led to clinical improvement and normalization of inflammatory markers. This case emphasizes the need to consider Rosai-Dorfman disease in the differential diagnosis of thyroid masses.