Recurrent episodes of hypothermia as a sequela of human herpesvirus 6 encephalitis following cord blood transplantation for acute myeloid leukemia

: A 46-year-old female patient underwent a cord blood transplantation (conditioning regimen: fludarabine/busulfan4/melphalan80; graft-versus-host disease (GVHD) prophylaxis: tacrolimus + mycophenolate mofetil) for acute myeloid leukemia (AML) with her 1st hematological complete response to induction therapy (idarubicin 3 days+cytarabine 7 days). She lost her consciousness due to human herpesvirus 6 (HHV-6) encephalitis on day 31, and therefore, we increased the foscarnet dosage (from 120 mg/kg to 180 mg/kg). Her consciousness level improved after treatment. However, 8 hours of sudden hypothermia occurred with hyperhidrosis, hypertension, and subsequent hyperglycemia on day 34. Her condition did not improve even after administration of anticonvulsant, steroid pulse, or intravenous immunoglobulin. A total of 75 attacks were observed until she was discharged on day 471. She has not shown chronic GVHD or relapsed AML since then. However, HHV-6 caused prolonged damage to her hypothalamus as observed through magnetic resonance imaging (MRI) and single-photon emission computed tomography (SPECT) using 99mTc ethyl cysteinate dimer even when the virus was not detected from her cerebrospinal fluid. This damage can be responsible for the hypothermia attacks. This is the first case report of prolonged series of hypothermia attacks for over a year as a sequela of HHV-6 encephalitis after a cord blood transplantation for AML.