Langerhans cell histiocytosis: A diagnostic challenge on thyroid fine needle aspiration cytology.

Thyroid gland involvement by Langerhans cell histiocytosis (LCH) is extremely rare. A 28-year-old woman with a history of polyuria, polydipsia and amenorrhoea presented with a diffuse thyroid swelling of 2 months duration. Clinical diagnosis was diabetes insipidus. Endocrine profile was normal. Fine needle aspiration cytology (FNAC) from thyroid revealed numerous large histiocytes with prominent nuclear grooves against an inflammatory background rich in eosinophils. A diagnosis of LCH was made and immunocytochemistry with CD1a confirmed the same. Subsequent skin biopsy also showed LCH. FNAC diagnosis of LCH in thyroid is challenging. The diagnostic pitfalls range from thyroiditis due to the presence of inflammatory cells in the background to papillary thyroid carcinoma due to grooved nuclei. Additional material should be collected at FNAC for ancillary studies to confirm the diagnosis.