[Extra-nodal Rosai-Dorfman disease: a case report with thyroid involvement].

Extra nodal involvement by Rosaï-Dorfman disease (RDD) is not rare but remains poorly described clinically and microscopically. We report a case of RDD involving the thyroid and revealed by a 15 mm cold nodule developed on an ancient goiter. The patient was a 53 year old North African woman. She also presented an involvement of cervical lymph nodes, respiratory tract and right kidney. Microscopic analysis of thyroid revealed a diffuse and dense infiltrate of large pale histiocytes with few features of lymphophagocytosis. To the best of our knowledge, this is the fifth case reported in the literature. In previous reported cases, thyroid RDD was associated to constant lymph node involvement (massive lymphadenopathy in 3 cases and occult in one case) and no other extra nodal localization except the respiratory tract in one case. The characteristic features of lymphophagocytosis must be searched with great care.