DISCUSSION:
We report a rare case of polyviral retinitis in a post-allogeneic stem cell transplant patient, with PCR of the aqueous fluid demonstrating two viral populations, CMV and VZV, which occurred despite ongoing prophylaxis for these two viruses, and despite completing two courses of treatment for CMV viremia, with a documented negative CMV PCR in the blood prior to the presentation with retinitis. CMV sensitivity testing performed indicated sensitivity to both agents used for previous treatment (Ganciclovir and Foscarnet)8. As the CMV serum PCR was undetectable at the time of the presentation with CMV retinitis, it is unlikely that this presentation was driven by resistance to treatment. Presentation of CMV retinitis was likely multifactorial driven by early CMV reactivation, low CD4 counts and delayed CD4 lymphocyte recovery in the first 100 days post-transplant which are all associated with late CMV disease. Other potential contributing factors are poor CNS and poor retinal penetration of Letermovir. With very little existing literature on either mixed viral retinitis or CMV retinitis during Letermovir prophylaxis9, this case serves to expand the literature on both topics. The case also highlights the need to expand efficacy data on secondary prophylaxis with Letermovir to address an unmet therapeutic need. To our knowledge this represents the first documented case of mixed viral retinitis in this therapeutic context.