Human herpes virus (HHV)6-associated limbic encephalitis and/or myelitis is one of the life-threatening central nervous system complications following allogeneic hematopoietic stem cell transplantation (HSCT). Recent reports have shown significant correlations of these complications with unrelated cord blood transplantation (UCBT). We retrospectively analyzed 228 allogeneic HSCT recipients in our single institution; 13 patients (5.7%) were diagnosed with HHV6-associated encephalitis/myelitis. This complication was documented in 8 of 51 UCBT recipients (15.7%) and 5 of 177 recipients (2.8%) transplanted with bone marrow or peripheral blood stem cells, indicating a higher incidence of this complication occurring in UCBT recipients (P =0005). In addition, HHV6-associated encephalitis/myelitis occurred more frequently in recipients who underwent 2 or more HSCTs (7 of 59 recipients [11.9%]), compared to those who received only 1 HSCT (6 of 169 recipients [3.6%], P =018). Of note, the incidence of this complication increased to 28.6% (6 of 21 recipients), when the analysis was restricted to a second or more UCBT recipients. All 13 patients presented preengraftment immune response prior to the onset of encephalitis. Two patients manifested typical symptoms at the onset of HHV6-associated encephalitis/myelitis, such as memory dysfunction, disorientation, and consciousness disturbance. However, 4 patients presented only with dysesthesia and pruritus, described as typical manifestations of patients with calcineurin-inhibitor-induced pain syndrome (CIPS), and the remaining 7 showed both symptoms, indicating that CIPS-like symptoms might be manifestations of HHV6-associated myelitis. Thus, physicians should be alert to this rare but often fatal complication, particularly for those who receive 2 or more HSCTs using UCB.
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