Objective:

To delineate the clinical and PET/CT metabolic imaging characteristics across the spectrum of visceral leishmaniasis (VL) and associated hemophagocytic lymphohistiocytosis (HLH), and to develop a simple risk score for identification of patients at risk of VL-HLH.

Approach:

• Study Design: This retrospective study enrolled 21 VL patients categorized into three groups: visceral leishmaniasis only (VL-only, n=7), VL-HLH (n=8), and a clinically indeterminate Grey Zone group (n=6).
• Clinical Comparison: Clinical and laboratory parameters were compared across groups.
• Metabolic Analysis: For 9 patients with PET/CT, metabolic patterns and correlations between splenic SUVmax and serological markers were analyzed.
• Risk Score Development: A simple risk score was constructed based on significant indicators and evaluated across groups.

Key Findings:

• No differences were observed in age, sex, and main symptoms among the three groups.
• Compared to the VL-only group, the VL-HLH group exhibited significantly higher levels of the inflammatory marker C-reactive protein and greater spleen thickness (P<0.05).
• PET/CT identified the spleen and bone marrow as primary metabolic target organs.
• Splenic SUVmax showed strong positive correlations with D-dimer (r=0.82, p<0.01) and ferritin (r=0.69, p<0.05).

Interpretation:

The study reveals a systemic 'inflammation-coagulation-tissue injury' network in VL, with the spleen as a core metabolic target.

Limitations:

• Small sample size of 21 patients.
• Retrospective design may limit the generalizability of findings.

Conclusion:

The proposed simple stratification tool based on C-reactive protein and spleen thickness serves as a practical instrument for clinical risk warning.