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

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.