A Case of Pediatric Subcutaneous Panniculitis-like T-cell Lymphoma (SPTCL) presenting as HLH

Background/Objectives: Cutaneous T-cell lymphoma (CTCL) is an uncommon diagnosis in the pediatric population, and among its subtypes, subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is exceedingly rare. We present a unique case of pediatric SPTCL initially manifesting as hemophagocytic lymphohistiocytosis (HLH), with diagnosis established only after a skin biopsy. This report aims to highlight diagnostic challenges and therapeutic complexity in such presentations. Methods: We conducted a detailed case review of a pediatric patient who presented with HLH. Extensive in-fectious, autoimmune, and oncologic evaluations were performed prior to diagnostic skin biopsy. Genetic testing was also conducted to assess for germline mutations, including HAVCR2. Results: The patient was ultimately diagnosed with SPTCL following histopathological analysis of skin tissue. His disease course was marked by significant complications, including recurrent HLH episodes. Multiple therapeutic regimens, including immunosuppressants and chemotherapy, were trialed with varying success. Genetic analysis revealed a HAVCR2 mutation, raising important considerations regarding disease pathogenesis and therapeutic direction. Conclusions: This case underscores the importance of considering SPTCL in pediatric HLH of unknown origin and highlights the diagnostic value of skin biopsy. The presence of a HAVCR2 mutation complicates treatment planning and calls into question the appropriateness and timing of hematopoietic stem cell transplantation in this rare population. Greater understanding of the molecular drivers of SPTCL is needed to guide future management strategies.