While BNS usually presents in a patient who has been diagnosed with Waldenstrom's macroglobulinemia it occasionally may be the presenting finding.
Findings which can help to make the diagnosis of BNS:
(1) CSF analysis showing monoclonal IgM and lymphoplasmacytoid cells.
(2) Flow cytometry of the CSF showing monoclonal lymphoid cells with CD19, CD20, CD79a,CD79b, CD27, CD52, CD138 and IgM).
(3) MRI demonstration of leptomeningeal infiltration or a mass lesion (tumoral).
(4) A CNS biopsy (guided by imaging studies) showing lymphoplasmacytoid cells with immunoglobulin gene rearrangement
(5) Demonstration of the MYD88 L265P mutation
(6) Exclusion of alternative diagnoses (hyperviscosity, other lymphoproliferative disorder, infection, etc).
