Isolated leptomeningeal infiltration of a primary CNS B-cell lymphoma diagnosed by flow cytometry and confirmed by necropsy

Background The diagnosis of the isolated leptomeningeal involvement of a primary central nervous system B‐cell lymphoma without parenchyma lesions may be difficult. Patients with leptomeningeal meningeosis lymphomatosa can present with various neurologic deficits. Aims of the study To demonstrate the impact of cerebrospinal fluid (CSF) flow cytometry in the diagnosis of an isolated leptomeningeal manifestation of B‐cell lymphoma by presenting an interesting case report. Methods Flow cytometric analysis of B‐cell monoclonality of the CSF was performed as complementary diagnostic procedure in addition to CSF cytology. Final diagnosis was confirmed by necropsy. Results We suspected isolated leptomeningeal manifestation of B‐cell lymphoma with palsy of the VI and VII cranial nerves in a 79‐year‐old male, because of mononuclear pleocytosis in CSF. Interestingly, the decisive diagnostic hint was given by implementation of flow cytometry of the CSF. Diagnosis was confirmed by postmortem autopsy. Conclusion Our case shows that flow cytometry of the CSF in addition to conventional CSF cytology has the potential to accelerate diagnosis of lymphomeningeal infiltration of B‐cell lymphoma.