A case of Epstein–Barr virus infection presenting with facial nerve palsy following the precursor condition of hemophagocytic lymphohistiocytosis

A 25‐year‐old man with infectious mononucleosis caused by Epstein–Barr virus infection developed facial nerve palsy. He was admitted to the hospital due to prolonged fever with liver enzyme elevations, diagnosed as primary Epstein–Barr virus infection. During conservative management, his fever and liver dysfunction persisted, with elevated serum inflammatory marker levels, and the precursor state of Epstein–Barr virus‐associated hemophagocytic lymphohistiocytosis was suspected. Although his symptoms and liver dysfunction trended toward amelioration after short‐term prednisolone, left‐sided facial palsy developed acutely. Facial palsy was considered Epstein–Barr virus infection‐related, and he recovered within 1 month following additional steroid therapy. Given the presence of the precursor condition of hemophagocytic lymphohistiocytosis just prior to facial palsy, hypercytokinemia was considered a possible pathogenic mechanism for the facial palsy. In patients with Epstein–Barr virus infection, facial palsy may occur independently of the recovery of other symptoms, and cytokine disturbance may affect its development.