Commentary:Herpes simplex virus and SLE: though uncommon yet with significant implicationsNaim Mahroum1, Abdulrahman Elsalti1, Yehuda Shoenfeld21International School of Medicine, Istanbul Medipol University, Istanbul, Turkey.2Zabludowicz Center for autoimmune diseases, Sheba Medical Center, Ramat-Gan, Israel.Running title : Commentary: Herpes simplex virus and SLE: though uncommon yet with significant implicationsKeywords – Autoimmunity, infection and autoimmunity, systemic lupus erythematosus, human herpes viruses, herpes simplex virus

Background: Fever of unknown origin (FUO) is a diagnostic challenge. Positron emission tomography with computed tomography (PET/CT) is expensive and not widely available. We aimed to evaluate the diagnostic yield of PET/CT in the workup of FUO, and identify the patients for whom this test is most useful. Methods: We reviewed the records of all patients admitted to Sheba Medical Center from 2013 to 2017 who were underwent PET/CT for the evaluation of FUO. Results: Of the 128 patients included, PET/CT was helpful in revealing the cause of FUO in 61 (48%). A final diagnosis was made in 95 (74%) patients. Of the 128 PET/CT tests conducted for the workup of FUO, 61 (48%) had true positive results, 25 (20%) false positive results, 24 (19%) true negative results, and 18 (14%) false negative results. In a multivariate analysis, helpfulness of PET/CT was independently associated with weight loss and low hemoglobin. The calculated test sensitivity was 77%, specificity was 49%, positive predictive value was 71% and negative predictive value was 57%. Conclusion: PET/CT is valuable in the diagnostic workup of FUO. When used as a complementary test, it was helpful in diagnosing almost half the patients, and especially in those with low hemoglobin and weight loss.