Cytological Diagnostic Approach in 3 Cases of Langerhans Cell Histiocytosis Presenting Primarily as a Thyroid Mass

Background: Langerhans cell histiocytosis (LCH) is a monoclonal disease of specialised histiocytes characterised by the proliferation of neoplastic Langerhans cells (LCs) with a varying admixture of mature lymphocytes, eosinophils and plasma cells. LCH commonly occurs in the paediatric population and young adults with the involvement of bone, skin and lymph nodes. LCH has a protracted clinical course with an overall mortality rate of 3%. Primary involvement of the thyroid gland in LCH at presentation is a rare phenomenon that can result in misdiagnosis with consequent mismanagement. Case: Ultrasound-guided fine-needle aspiration cytology (FNAC) of the thyroid was performed in 3 cases at a tertiary cancer centre, including 2 referral cases where the patient presented with the only symptom of progressive thyroid enlargement. These cases were reported initially or on review and the results were correlated with histology/ancillary techniques. A cytological diagnosis of suspicion for LCH was offered in 2 cases at our centre and 1 case was referred to our centre with a diagnosis of suspected papillary thyroid carcinoma. On review of outside smears at our centre, the diagnosis was changed to suspected LCH. The diagnosis was confirmed by immunopositivity for CD68, CD1a and S100 in 1 case and Tru-cut biopsy followed by immunohistochemistry for CD1a, S100, TTF-1 and LCA in the other 2 cases. Conclusion: FNAC was helpful in accurately diagnosing LCH even though the presentation was unusual. Thus, unnecessary surgery was obviated.