H1N1‐Related Hemophagocytic Lymphohistiocytosis Complicated by Severe Rhabdomyolysis in a Pediatric Patient: A First Case Report

Background Hemophagocytic lymphohistiocytosis (HLH) is a rare and often life‐threatening hyperinflammatory disorder, mainly caused by infections, malignancies, or autoimmune diseases. Influenza A (H1N1) has occasionally been linked to pediatric HLH cases. Rhabdomyolysis, relatively uncommon in children, can be a complication of viral infections, including influenza. To our knowledge, this is the first reported pediatric case where H1N1 infection was complicated by both HLH and severe rhabdomyolysis. Case Presentation We describe the case of a previously healthy 4‐year‐old girl who was hospitalized with high fever, gastrointestinal symptoms, and marked somnolence. Blood tests revealed severe rhabdomyolysis (creatine phosphokinase CPK > 100,000 U/L) and metabolic acidosis. Influenza A (H1N1) infection was confirmed by a nasopharyngeal swab. Despite prompt initiation of antiviral and supportive therapies, the patient developed persistent fever, pancytopenia, hyperferritinemia, hypertriglyceridemia, hepatosplenomegaly, and cardiac involvement. Bone marrow biopsy confirmed hemophagocytosis, according to HLH‐2004 criteria. She was treated with high‐dose methylprednisolone and intravenous immunoglobulin (IVIG), with rapid clinical improvement. The patient was discharged after 16 days without sequelae. Conclusions This case describes a rare but severe presentation of Influenza A infection in a child, complicated by both HLH and severe rhabdomyolysis. The combination of a hyperinflammatory condition and multiorgan dysfunction highlights the importance of early recognition and multidisciplinary management. Our case is the first documented pediatric case of H1N1‐related HLH with severe rhabdomyolysis in pediatric populations, and a review of the literature confirms the rarity of this association. Clinicians should maintain a high index of suspicion for HLH in children with persistent fever, cytopenia, hyperferritinemia, and organ involvement during viral infections. The potential coexistence of rhabdomyolysis should be considered in the presence of persistent high CPK levels to prevent serious complications such as acute kidney injury.