HHV-6 encephalitis: Mayo clinic finds a high rate of severe hippocampal atrophy and neurological deficits

A Mayo clinic review of long-term outcome of patients with HHV-6 encephalitis showed that over 60% showed persistent sequelae associated with severe bilateral hippocampal atrophy. Symptoms included anterograde amnesia, aphasia, headaches, confusion and persistent memory deficits.

The investigators identified 10 allogenic hematopoietic cell transplant patients over five years, representing 1.7% of allogenic transplant recipients and 7.1% of cord blood transplants.

Of interest, the plasma PCR was HHV-6 negative in two patients in spite of being HHV-6 positive in the CSF. Also, there was a delay in many cases before evidence of injury from HHV-6 encephalitis could be seen on an MRI. Several cases that looked normal at the outset revealed significant hippocampal atrophy at 5-12 weeks, in spite of ganciclovir therapy.

The most common abnormality was increased T2 signal in the bilateral hippocampus (50%) and mesial temporal lobe (38%). In several patients, residual neurologic deficits persisted in spite of normal or improved MRI results.

CSF cell count was normal in half the patients, consistent with past literature.

A large Japanese retrospective study of 145 patients with encephalitis previously found that 20% died within 100 days, and the remaining 57% were left with significant neurological sequelae (Ogata 2017). This study determined that foscarnet resulted in fewer deaths and neurological sequlae than ganciclovir. Foscarnet is approved for HHV-6 encephalitis in Japan.

Read the full Mayo clinic study: Fida 2019