Human Herpes Virus-6-Associated Encephalitis/Myelitis Mimicking Calcineurin Inhibitor-Induced Pain Syndrome in Allogeneic Stem Cell Transplantation Recipients.

Human herpes virus-6 (HHV6)-associated myelitis and calcineurin inhibitor-induced pain syndrome (CIPS) are serious complications of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Because these 2 complications cause similar sensory nerve-related symptoms, such as paresthesia, pruritus, and severe pain occurring around the engraftment, it can be difficult to differentially diagnose the 2 conditions. We retrospectively analyzed 435 recipients to distinguish clinical symptoms of these 2 complications. Twenty-four patients (5.5%) developed HHV6-associated encephalitis/myelitis; of these, 11 (2.5%) presented only with myelitis-related symptoms (HHV6-associated myelitis), which was confirmed by the detection of HHV6 DNA, and 8 (1.8%) had CIPS, with undetected HHV6 DNA. All patients with HHV6-associated myelitis or CIPS exhibited similar sensory nerve-related symptoms. Diagnostic images did not provide definite evidence specific for each disease. Symptoms of all patients with CIPS improved after switching to another immunosuppressant. Overall survival rate at 2 years for patients with HHV6-associated encephalitis/myelitis was significantly lower than that of CIPS (13.1% versus 29.2%; P = .049) or that of patients without HHV6-associated encephalitis/myelitis or CIPS (42.4%; P = .036), whereas there was no significant difference among the latter 2 groups (P = .889). The development of HHV6-associated encephalitis/myelitis but not CIPS was significantly associated with poor prognosis. Thus, transplant physicians should be aware that sensory nerve-related symptoms indicate early manifestations that might be correlated with reactivation of HHV6 or CIPS. Therefore, identification of HHV6 DNA is crucial for making a differential diagnosis and immediately starting appropriate treatments for each complication.