The Role of Neutrophil-to-Lymphocyte Ratio as A Potential Biomarker of Erythema Nodosum Leprosum Disease Severity: A Retrospective Study

Background: Erythema nodosum leprosum (ENL) is an acute immunologic complication of multibacillary leprosy (MB) that causes systemic inflammation in various organs. It is a major factor contributing to morbidity, mortality, and financial hardship. ENL is diagnosed clinically, and objective indicators for severe conditions remain unexplored. Simple blood biomarkers that differentiate between different ENL disease severity levels are required. Neutrophilto-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) have been widely studied as severity biomarkers of numerous neoplastic and inflammatory disorders. Objective: We examined NLR and PLR values at various ENL severities and their role as severe disease indicators for ENL. Methods: This cross-sectional retrospective study examined 246 patients with multibacillary leprosy—with and without ENL reactions and aged 18 and above—and calculated their NLR and PLR values. Then, we compared patients with mild and severe disease states to those without ENL. The severity classification was based on the ENLIST ENL Severity Score (EESS). To determine the NLR and PLR cutoff points of mild and severe ENL, a receiver operating characteristic (ROC) curve was constructed. Results: The NLR value for severe ENL was significantly higher than that for mild ENL (p < 0.05), with a severe disease cutoff point of 5.71 (95.7% sensitivity, 68.7% specificity). No significant differences were found in PLR between patients with mild and severe ENL. Conclusion: While PLR is not an effective assay for evaluating ENL severity, NLR is a potential biomarker for severe ENL reactions in patients with multibacillary leprosy.