White Blood Cell Count and Lymphocyte-to-monocyte Ratio as a Screening Tool for Predicting Intravascular Lymphoma in the Differential Diagnosis of Fever of Unknown Origin

Objective Intravascular large B-cell lymphoma (IVLBCL) is a critical cause of fever of unknown origin (FUO). While a pathological analysis is essential for diagnosing IVLBCL, the indications for an invasive procedure may be ascertained using easy, non-invasive tests. The lymphocyte-to-monocyte ratio (LMR) can reportedly predict the diagnosis of malignant lymphoma in patients with lymphadenopathy; however, its clinical utility in predicting an IVLBCL diagnosis in patients with FUO remains to be elucidated. Methods The medical records of 91 patients with FUO who underwent a skin biopsy for suspected IVLBCL between January 2010 and April 2023 were retrospectively reviewed. Patients Seventeen and 60 patients with and without pathologically diagnosed IVLBCL, respectively, were included in the analysis. The laboratory data nearest to the timing of the skin biopsy were then compared between the groups. Results Among the variables with an intragroup difference, a low white blood cell (WBC) count and LMR were predictors of an IVLBCL diagnosis after adjusting for covariates. A receiver operating characteristic analysis demonstrated that a WBC ≤7,200 and LMR ≤3.0 predicted the diagnosis with a sensitivity of 88.2% and 100%, and a specificity of 65.0% and 43.3%, respectively. In addition, the probability of IVLBCL increased to 71.4% in patients with both variables but was 0% in those with neither variable, indicating its potential utility in determining the need for an invasive procedure. Conclusion The WBC count and LMR predicted an IVLBCL diagnosis in patients presenting with FUO.