Kikuchi-Fujimoto Disease and COVID-19 vaccination: pharmacovigilance approach.

Summary: Background. Kikuchi-Fujimoto Disease (KFD) or histiocytic necrotizing lymphadenitys is a rare disorder characterized by subacute necrotizing regional lymphadenopathy. It is usually presented as painful cervical nodes and associated with fever, headache, night sweats, nausea, vomiting and sore throat. Etiology of KFD is still unclear, two theories have been proposed: infections and autoimmune origin. Due to recent reports of KFD related to COVID-19 vaccination, the novelty of the mechanism of these vaccines and the immunomodulated role of both matters, a literature and adverse event databases review was carried out in order to shed light on the relationship between these two matters. Methods. A search in the Spanish and the European adverse events databases (FEDRA and Eudravigilance) was performed. Search criteria were any drug and the diagnosis "Histiocytic necrotizing lymphadenitis" according to the Medical Dictionary for Medical Activities version 25.0. All adverse events registered as June 2, 2022, were included. Results. FEDRA encompassed two KFD reports, one related to a mRNA COVID-19 vaccine. Eudravigilance included a total of 62 KFD cases, 14 of them associated to COVID-19 vaccines and eight to other vaccines. Conclusions. Pharmacovigilance is of utter importance in detecting adverse events caused by new vaccines. More research is needed to establish a final connection between KFD and COVD-19 vaccines, but due to the physiopathology of the condition, how vaccines stimulate the immune system and the high number of reported KFD cases with vaccines given its rare incidence, it is plausible to think that both entities are related.