# Localised Kikuchi–Fujimoto Disease With Mediastinal Lymphadenopathy: A Case Initially Mimicking Malignant Lymphoma on Endobronchial Ultrasound‐Guided Transbronchial Needle Aspiration Cytology

## TL;DR

A rare case of Kikuchi–Fujimoto disease in the mediastinum was initially mistaken for cancer, highlighting the need for surgical biopsy for accurate diagnosis.

## Contribution

Reports a rare case of mediastinal Kikuchi–Fujimoto disease misdiagnosed as lymphoma using EBUS-TBNA cytology.

## Key findings

- EBUS-TBNA cytology suggested malignant lymphoma but was later found to be KFD.
- Surgical biopsy confirmed the diagnosis of KFD with massive necrosis and histiocytic infiltration.
- The case emphasizes the diagnostic limitations of EBUS-TBNA in atypical KFD presentations.

## Abstract

Kikuchi–Fujimoto disease (KFD), also known as histiocytic necrotising lymphadenitis, is a benign, self‐limiting disorder that primarily affects young women and is typically characterised by fever and cervical lymphadenopathy. However, isolated mediastinal lymphadenopathy without cervical involvement is rare. We report the case of a 37‐year‐old woman who presented with persistent fever and mediastinal lymphadenopathy. Endobronchial ultrasound‐guided transbronchial needle aspiration (EBUS‐TBNA) cytology of the lymph nodes revealed necrosis and atypical lymphoid cells, highly suggestive of malignant lymphoma. Owing to diagnostic difficulties, video‐assisted thoracoscopic excision was performed to obtain a definitive diagnosis. Histopathological examination confirmed KFD with massive necrosis and histiocytic infiltration. The patient underwent symptomatic treatment and remained under long‐term follow‐up. This case highlights the rarity of mediastinal‐limited KFD and the diagnostic pitfall of EBUS‐TBNA cytology, emphasising that surgical biopsy is critical for an accurate diagnosis when malignancy is suspected in this atypical presentation.

We report a rare case of isolated mediastinal Kikuchi–Fujimoto disease (KFD) in a 37‐year‐old woman, which was initially misinterpreted as malignant lymphoma based on EBUS‐TBNA cytology. Definitive diagnosis was achieved through video‐assisted thoracoscopic surgery, revealing characteristic massive necrosis and histiocytic infiltration. This case highlights the diagnostic pitfalls of EBUS‐TBNA in atypical KFD presentations and underscores the necessity of surgical biopsy for an accurate diagnosis.