Neurological and neuropsychiatric manifestations in a teenager with familial haemophagocytic lymphohistiocytosis with STXBP2 mutation.

Familial haemophagocytic lymphohistiocytosis (FHLH) is a rare, life-threatening immune disorder. We report a teenager who experienced several months of low mood, fatigue and progressive lower limb weakness; symptoms which had previously been attributed to a psychosomatic disorder before admission. Clinical findings included lower limb neurological deficits, thrombocytopenia and splenomegaly. Further investigation revealed neuroinflammation on MRI, progressive cytopenias, raised inflammatory markers and elevated protein in the cerebrospinal fluid. Bone marrow aspirate identified haemophagocytosis, and an STXBP2 mutation on genetic testing confirmed FHLH as the diagnosis. Treatment followed the HLH-94 protocol, including intrathecal methotrexate for central nervous system involvement. This case highlights the importance of considering HLH in children with atypical neuropsychiatric presentations. It emphasises the need for early, multidisciplinary intervention for timely diagnosis and effective treatment with immunosuppressants before bone marrow transplant.