Case Report: Hemophagocytic lymphohistiocytosis after SARS-CoV-2 infection revealing clinically diagnosed stage IVB diffuse large B-cell lymphoma in quiescent adult-onset Still's disease.

BACKGROUND

Adult hemophagocytic lymphohistiocytosis (HLH) may be triggered by infection, malignancy, or systemic inflammatory disease. Attribution is challenging when recent SARS-CoV-2 infection, quiescent adult-onset Still's disease (AOSD), and an occult B-cell clonal disorder coexist.

CASE REPORT: A 71-year-old man with AOSD controlled for 14 years on low-dose methotrexate developed persistent fever and fatigue after mild SARS-CoV-2 infection. He subsequently developed cytopenias, hyperferritinemia, markedly elevated lactate dehydrogenase, diffuse FDG-avid lymphadenopathy, hepatosplenomegaly, elevated soluble interleukin-2 receptor, reduced natural killer-cell activity, and bone marrow hemophagocytosis, fulfilling HLH criteria. Broad pathogen evaluation, including blood and bone marrow metagenomic next-generation sequencing, did not identify an alternative infectious trigger. Bone marrow histopathology did not show definite tumor cells; however, flow cytometry identified monoclonal mature B cells, and peripheral-blood smear high-throughput sequencing detected lymphoma-associated mutations including MYD88, CD79B, IGLL5, PRDM1, DTX1, DUSP2, and BTG1. Multidisciplinary consultation favored probable lymphoma-associated HLH with clinically diagnosed stage IVB diffuse large B-cell lymphoma. HLH-directed therapy followed by rituximab-based lymphoma-directed chemotherapy led to transient clinical improvement, but the patient later died from infectious complications.

CONCLUSION

Mild SARS-CoV-2 infection may act as a co-trigger or unmasking event rather than the sole cause of HLH. Persistent high lactate dehydrogenase and soluble interleukin-2 receptor, diffuse lymphadenopathy, clonal mature B cells, lymphoma-associated mutations, and negative broad pathogen testing should prompt evaluation for occult lymphoma-associated HLH.