HHV-6 reactivation is one of the most common causes (in 30-70% of patients) of encephalitis in allo-SCT. It is a ubiquitous viral infection that remains latent and can reactivate after transplant.
Risk factors: HLA mismatch, T-cell depletion therapy, treatment with glucocorticoids, and the use of cord blood as a source of stem cells; 90% of cases of HHV-6 reactivation occur in patients who with cord-blood transplants.
Encephalitis presents as subacute confusion, but some may have a more progressive course. Anterograde amnesia, personality changes, irritability and seizures. SIADH is common.
CSF analysis shows mild lymphocytic pleocytosis and protein elevation.
Treatment is based on in-vitro susceptibility testing and foscarnet is therapy of choice. Can add ganciclovir if not clinically improving. But need to monitor closely for side effects including bone marrow suppression and electrolyte derangement which can predispose to seizures. Alternative therapy is cidofovir, but watch out for nephrotoxicity. Duration is 3-6 weeks and you shouldn’t monitor PCR levels to shorten treatment duration.
Notes from: N Engl J Med 2018; 378:659-669