Increased neopterin in cerebrospinal fluid in active adult neurohistiocytosis

Diagnosis of neuro-histiocytosis is challenging and relies on clinical presentation, imaging, and cerebrospinal fluid (CSF) analysis to exclude differential diagnoses. Brain biopsy remains the gold standard for accurate diagnosis, but it is rarely performed because of the risk of the procedure and the low rentability in neurodegenerative presentation. Therefore, there is an unmet need to identify a specific biomarker for diagnosing neurohistiocytosis in adults. Because microglia (brain macrophages) is involved in the pathogenesis of neurohistiocytosis and produces neopterin secondary to aggression, the purpose of our study was to evaluate the value of the CSF neopterin levels for the diagnosis of active neurohistiocytosis. Of the 21 adult patients with histiocytosis, four patients had clinical symptoms compatible with neurohistiocytosis. In the two patients with a confirmed diagnosis of neurohistiocytosis, CSF neopterin levels were elevated as well as IL-6 and IL-10 levels. In contrast, the two other patients in whom the diagnosis of neurohistiocytosis was infirmed and all other patients with histiocytosis without active neurological disease involvement had normal CSF neopterin levels. In summary, increased CSF neopterin concentration represented a valuable tool for diagnosing active neuro-histiocytosis in adults with histiocytic neoplasms in this preliminary study.