The Morphological Landscape of Bone Marrow Findings in Visceral Leishmaniasis

Background and aim Visceral leishmaniasis (VL) remains a major parasitic disease globally, with a high burden in the Indian subcontinent. Diagnosis relies on identifying Leishmania donovani amastigotes in bone marrow aspirates and biopsies; however, detailed characterization of associated marrow morphology is limited in the current literature. This study aimed to analyze bone marrow aspirate and trephine biopsy findings in visceral leishmaniasis and assess correlations between parasite load and key hematological parameters. Methods This retrospective study included 42 confirmed VL cases diagnosed between January 2003 and March 2025 at a tertiary center hospital in India. Clinical data, peripheral blood films, bone marrow aspirates (Romanowsky stain), and trephine biopsies (hematoxylin-eosin stain) were reviewed. Average parasite density (APD) was quantified using standardized oil immersion counts. Morphological features, including cellularity, plasmacytosis, hemophagocytosis, and stromal changes, were recorded. Statistical associations between APD and clinical or hematological variables were assessed using chi-square and Fisher's exact tests. Results The cohort (M:F=2.8:1; aged 5-55 years) universally presented with fever (n=42; 100%), with splenomegaly (n=37; 88.1%) and hepatomegaly (n=33; 78.6%) commonly observed. Pancytopenia was observed in 73.8% (n=31) of cases. Bone marrow findings included hypercellularity (n=34; 80.95%), plasmacytosis (n=37; 88.0%), increased histiocytes (n=34; 80.9%), and hemophagocytosis (n=22; 52.38%). APD distribution was as follows: 1+ (n=6; 14.29%), 2+ (n=16; 38.10%), 3+ (n=13; 30.95%), and 4-5+ (n=7; 16.6%). Higher parasite load correlated significantly with splenomegaly (p=0.031), pancytopenia (p=0.018), and plasmacytosis (p=0.024). Additional findings included dyserythropoiesis (n=16; 38.1%), increased eosinophilic precursors (n=18; 42.86%), myelofibrosis (n=6; 14.2%), and a rare case of gelatinous transformation. Conclusion Combined assessment of aspirate cytology and trephine histology enhances diagnostic sensitivity in VL. Recognition of characteristic marrow alterations supports timely diagnosis and reduces unnecessary investigations, particularly in non-endemic settings.