Kikuchi-Fujimoto disease associated with community acquired pneumonia showing intrathoratic lymphadenopathy without cervical lesions

INTRODUCTION: Kikuchi-Fujimoto disease (KFD), or histiocytic necrotizing lymphadenitis, is a rare entity of unknown etiology in young adults that is typically characterized by cervical lymphadenopathy and persistent fever. The pathogenesis of KFD has been suggested to be an abnormal immune response, and infections or autoimmune diseases are considered to be involved in KFD. However, KFD associated with community acquired pneumonia (CAP) has not been reported. CASE DESCRIPTION: A 35-year-old male was admitted due to high fever, diffuse air-space consolidation in the right lung with ipsilateral pleural effusion and massive mediastinal and hilar lymphadenopathy without cervical lesions. On clinical suspicion of malignant lymphoma complicated with pneumonia, we performed a video-assisted thoracoscopic lymph node biopsy, and the diagnosis of KFD was established. Complete cure of the intrathoratic lesions was observed by administration of β-lactam antibiotics alone without steroid therapy. DISCUSSION AND EVALUATION: Previous large case series have identified no pathogenic relationship between KFD and pneumonia. The hilar adenopathy could have caused airway compression leading to pneumonia. CONCLUSIONS: KFD should be considered in the differential diagnosis of massive mediastinal and hilar lymphadenopathy, even when there are no superficial lesions. In addition, we need to bear in mind that unexpected disorders occasionally coexist with common diseases.