[Langerhans cell histiocytois of the thyroid: a rare disease not to be ignored].

Thyroid involvement by Langerhans cell histiocytosis is rare. We report the case of a ten-year old boy who presented with a 5 cm goitre. He was treated for diabetes insipidus 14 months before. Thyroid isotopic scan showed hypoactivity of right lobe and revealed a cold left nodule. The patient was treated by right lobo-isthmectomy with adjuvant corticotherapy and chemotherapy (vinblastine). He is well with 12 months follow-up. Microscopic analysis demonstrated a diffuse infiltrate of thyroid parenchyma by sheets of CD1a positive Langerhans cells associated with lymphocyte foci. This case is remarkable by the abundance of Langerhans cells and scarcity of eosinophils. The diagnosis of thyroid langerhans cell histiocytosis should not be ignored in both children and adult patients.