2713. Risk factors and clinical presentation of Herpes Simplex Virus Encephalitis in cancer patients

BACKGROUND: Herpes Simplex Virus Encephalitis (HSVE) can have lifelong sequelae. Presentation can be nonspecific in cancer patients. Cerebrospinal fluid testing may be falsely negative early in illness [1]. New immune-based or targeted radiation (RT) modalities may change risk, incidence of HSVE in cancer patients. METHODS: Retrospective study at Memorial Sloan Kettering Cancer Center (MSK). Review of records of patients with CSF meningitis/encephalitis (ME) PCR panels from 8/1/2016 to 7/31/2022. All unique patients who received brain RT at MSK during those dates were used to calculate incidence rates. RESULTS: 2749 patients had 5497 CSF analyses with ME panel. Of these, 12 tests from 10 patients showed HSV-1 or -2; 1 patient had relapsing HSVE and 3 positive HSV2 tests each done at least 6 months apart. Table 1 shows 10 patients with HSVE. 8 had solid tumors, 6 with receipt of chemo- or immunotherapy within 30 days. All solid tumor patients with HSVE had brain RT; 6 received steroids. 1 patient with relapsing HSVE was on immune checkpoint inhibitor (ICI). 4/8 patients with MRIs (Table 2) lacked typical findings; 4/8 patients with EEGs had focal temporal seizure activity. CSF pleocytosis was absent in 4/10 cases. 5 patients had residual deficits. 4 died due to progression of disease. Incidence of HSVE with brain radiation was 2.6/10,000 patient-years. [Figure: see text] [Figure: see text] CONCLUSION: General population incidence of HSVE ranges from 1-4 per million population per year [2]. Those receiving cancer treatment and brain RT have elevated HSVE risk. We found the risk after brain RT is much higher: 2.6/10,000 person-years. Only 1 of 10 patients in our series made a full recovery. Other key findings include: 1) One patient with recurrent HSVE in the setting of nivolumab: ICI combined with brain RT may increase risk of HSV reactivation. Such patients should be considered for high dose antiviral prophylaxis after a first HSVE episode. 2) Normal MR imaging and lack of CSF pleocytosis does not preclude HSVE diagnosis in clinically compatible illness. 3) No cases occurred among solid tumor patients treated with chemo- and/or immunotherapy only. Limitations: 1. Retrospective design. 2. Inclusion of lab confirmed cases only. DISCLOSURES: Mini Kamboj, MD , ASCO: speaker fee|Medscape: speaker fee|MJH life sciences: speaker fee|Regeneron: Advisor/Consultant|Web md: speaker fee