Illuminating the cytological intricacies of isolated filarial epitrochlear lymphadenitis: a case series of a seldom-seen clinicopathological occurrence with a review of the literature.

BACKGROUND: Lymphatic filariasis is a major parasitic disease caused by Wuchereria bancrofti, Brugia malayi, and Brugia timori, with India contributing a significant proportion of global cases. Although lymphadenitis commonly involves inguinal, axillary, or cervical nodes, isolated epitrochlear lymphadenopathy is exceptionally rare and can be mistaken for other infectious or neoplastic causes. Fine-needle aspiration cytology (FNAC) offers a rapid, cost-effective method for diagnosing filarial infections, especially when peripheral blood smears are negative. This study presents a series of isolated epitrochlear filarial lymphadenitis with a brief literature review to emphasize this unusual presentation.

METHODS: A retrospective review of cytopathology archives from July 2023 to June 2025 was conducted to identify cases of isolated epitrochlear filarial lymphadenopathy. Clinical findings, hematological data, cytomorphological features, and treatment outcomes were compiled. All smears were re-evaluated independently by 2 cytopathologists. A literature search using major databases, including PubMed, Scopus, Web of Science, and Google Scholar, was performed to identify previously reported cases, which were tabulated for comparison.

RESULTS: Three patients aged 25-48 years (2 males, 1 female) presented with solitary, painless, firm epitrochlear swellings measuring 1.5-3 cm, without systemic symptoms or additional lymphadenopathy. FNAC revealed sheathed microfilariae in all cases: B malayi in 2 patients and W bancrofti in 1, within a mixed inflammatory background. No granulomas, atypical cells, or microfilarial ova were identified. Peripheral blood smears were negative for microfilariae in all cases, though eosinophilia was noted in 1 patient. All individuals were treated with diethylcarbamazine citrate, showing complete resolution of lymphadenopathy within 4 weeks.

DISCUSSION AND CONCLUSION: Isolated epitrochlear lymphadenitis due to filarial infection is extremely uncommon and may be overlooked, especially in the absence of microfilaremia. This study underscores FNAC as a crucial diagnostic tool for detecting occult filariasis at atypical sites. Enhanced clinical suspicion and cytological evaluation in endemic regions can improve early diagnosis, guide timely therapy, and contribute to ongoing lymphatic filariasis elimination efforts.