Extremely elevated cerebrospinal fluid protein levels in a child with neurologic symptoms: beware of haemophagocytic lymphohistiocytosis.

Neurologic symptoms can be the initial manifestation of haemophagocytic lymphohistiocytosis (HLH). In this case study, we present a 3-year old boy with a clinical picture of encephalitis, a cerebrospinal fluid (CSF) protein level up to 1165 mg/dl and diffuse cerebral MRI abnormalities. The diagnosis of HLH was established only 6 weeks after initial presentation. The boy recovered after HLH therapy with persisting mild cognitive defects. Genetic investigation demonstrated X-linked lymphoproliferative disease (XLP) as the underlying cause of HLH. The extremely elevated protein level in CSF in this case has not yet been reported in patients with HLH.