Human herpesvirus 6 associated post-transplant acute limbic encephalitis: Clinical observations of biomarkers for risk of seizure in a pediatric population.

BACKGROUND: Human herpesvirus 6 (HHV6) is a cause of post-transplant acute limbic encephalitis (PALE). Seizures are associated with this disorder yet no predictive biomarkers have been identified. The objective of this study was to evaluate lab and neurodiagnostic biomarkers in patients with HHV6 associated PALE.

METHODS: A retrospective chart review was performed at our institutions between 2000 and 2017. Patients were identified through a clinical database. Inclusion criteria included: age less than 18 years, HHV6 (quantitative real-time PCR or meningoencephalitis panel) tested in CSF and serum. Biomarkers of serum and CSF viral load, EEG, and MRI were reviewed along with clinical data.

RESULTS: In total, 11 patients met inclusion criteria. All patients had undergone hematopoietic stem cell transplantation. Five of 11 patients had seizures as part of their clinical course, all being controlled with antiepileptic monotherapy. Seizure semiology was focal-onset in three cases and generalized in two. Neuroimaging was normal in all patients within seven days but six patients developed T2 signal intensities in the temporal lobes on repeat imaging between 14-28 days. The median CSF HHV6 viral load for all patients was 47 300 copies/mL although the median viral load was 2586 copies/mL in patients who had seizure compared to 473 969 copies/mL in those who had not (P = 0.02). Those with seizures tended to be younger (median 6.5 years compared to 11 years, P = 0.27). All patients with seizures had an EEG with 80% demonstrating abnormalities.

CONCLUSION: In patients with post-hematopoietic stem cell transplant HHV6 associated PALE, lower CSF viral load may be associated with a higher likelihood to have seizures. This may indicate a primary infection as opposed to secondary reactivation phenomenon.