Double Trouble in the Thyroid: Coexistence of Hurthle Cell Neoplasm and Microfilarial Infestation.

Lymphatic filariasis, though often asymptomatic, remains a pervasive parasitic disease in endemic regions worldwide. The incidental identification of microfilariae on fine-needle aspiration cytology (FNAC) smears is rare and their coexistence with thyroid neoplasms is exceedingly uncommon. To our knowledge, very few cases of thyroid malignancy with coexistent microfilarial infestation have been documented. We describe a compelling case of a 68-year-old female who presented with a thyroid nodule and underwent FNAC. Cytological analysis revealed features diagnostic of a Hürthle cell neoplasm, accompanied by the unexpected presence of Wuchereria bancrofti microfilariae. Remarkably, the patient exhibited no clinical signs of filarial infection, and peripheral blood examination showed neither microfilaremia nor eosinophilia. This rare cytological finding underscores the diagnostic breadth of FNAC, not only in the evaluating thyroid pathology but also in revealing occult parasitic infestations. It highlights the necessity of meticulous smear evaluation, especially in patients from endemic regions presenting with chronic nodular lesions. The detection of neoplastic and parasitic elements together illustrates the complex interplay between infectious and neoplastic processes and reaffirms FNAC's utility in identifying unexpected pathological associations.