Hürthle cell metaplasia in chronic lymphocytic thyroiditis: Role of age factor and review of literature on its molecular pathogenesis.

OBJECTIVES: Hürthle cell (HC) metaplasia is an important feature of chronic lymphocytic (Hashimoto) thyroiditis (HT). However, it is rarely observed in juvenile form HT. In a study based on fine needle aspiration cytology, the cytomorphological difference between pediatric HT and its adult form was studied, with special attention on HC metaplasia and its pathogenesis.

MATERIALS AND METHODS: The frequency of following 12 cytomorphological features in 16 pediatric and 104 adult HT cases were compared: follicular cells, lymphoid cells, HCs, plasma cells, lympho-histiocytic aggregates, epithelioid histiocytes, multinucleated giant cells, fire-flare appearance, colloid, intracytoplasmic lumen (ICL) with or without colloid inclusion, paravacuolar granules, and cyst cells. The age decade distribution of HC metaplasia was analyzed.

RESULTS: Significant difference was observed between pediatric HT and its adult form in respect of HC metaplasia and ICL with colloid inclusion in HC. HC were present in 7 (43.8%) of pediatric and 94 (90.4%) of adult HT cases (P = 0.00006). 1 (6.3%) pediatric and 35 (33.7%) adult HT cases had ICL with colloid inclusion in HC (P = 0.03698). As compared to first two decades of life, significantly higher number of cases revealed HC metaplasia in every decade from third decade onwards (P = 0.01290-0.00009); however, the difference in respect of ICL with colloid inclusions attained significance during sixth decade only (P = 0.00235).

CONCLUSIONS: Hürthlization, which appears to be survival response, is rare in pediatric HT and becomes more pronounced starting from third decade onwards; significant increase in ICL with colloid inclusion is a much more delayed phenomenon.