Background: Bing-Neel syndrome (BNS) is a rare central nervous system involvement of lymphoplasmacytic lymphoma (LPL). The diagnosis is made using a combination of cerebrospinal fluid (CSF) cytology, flow cytometry, detection of the MYD88 L265 mutation, and magnetic resonance imaging. CSF samples often have low cellularity, and LPL cells in CSF samples decay quickly, which makes diagnosis challenging. The driver mutation in 93-97% of LPL cases is MYD88 L265P (WHO Classification, 5th edition). Immunoglobulin heavy chain (IGH) gene rearrangements are frequently observed in LPL. With the rapid advancement of molecular diagnostic technologies, MYD88 L265P and IGH polymerase chain reaction (PCR) are widely available in diagnostic laboratories. We aimed to evaluate the use of MYD88 L265P and IGH PCR in the diagnosis and follow-up of BNS.

Methods: We retrospectively collected the data from electronic patient records. We included CSF samples from all patients with Bing-Neel syndrome treated at University College London Hospital between 2014 and 2024. Sample cellularity and morphology were assessed by cytology after cytospin. Blood-contaminated samples were excluded from further analysis. Good cellular samples were assessed by flow cytometry (Beckman Coulter Duraclone), followed by MYD88 L265P PCR (detection limit, 0.25%) and IGH PCR (detection limit, 1%) if there was sufficient sample. Acellular and low cellular (≤10 cells by cytology) samples were assessed only by MYD88 L265P PCR and IGH PCR.

Results: A total of 211 samples from 51 patients with BNS were included. Cytology analysis was performed on all samples after cytospin. 13/211 (6%) samples were blood contaminated and excluded from further analysis. Of the 198 clear CSF samples, 21/198 (11%) were acellular, and 89/198 (45%) were low cellular; therefore, they were insufficient for flow cytometry analysis. The remaining 88/198 (44%) samples were good cellular, which all showed a small, mature lymphocyte morphology.

Flow cytometry was performed on 82/88 cellular samples. 17/82 (20.7%) detected light-chain-restricted B lymphocytes; 12/17 had sufficient samples for MYD88 L265P and IGH PCR, which all (100%) confirmed clonality. 30/82 (36.6%) detected surface immunoglobulin-negative B lymphocytes by flow cytometry, which is highly suggestive of clonal B lymphocytes; 24/30 had sufficient samples for MYD88 L265P and IGH PCR; 23/24 (96%) confirmed clonality. 35/82 (42.7%) showed no clonal B lymphocytes by flow; 24/35 had sufficient samples for MYD88 L265P and IGH PCR; 6/24 (25%) confirmed clonality.

One hundred eleven samples were either acellular or low cellular. 44/111 were sent for MYD88 L265P and IGH PCR. 23/44 (52%) confirmed clonality.

Conclusion: Compared to flow cytometry, MYD88 L265P and IGH PCR are more sensitive in detecting clonal LPL cells. They are especially useful in follow-up samples and samples with low cellularity. In combination with typical lymphoplasmacytic lymphocyte morphology by cytology, MYD88 L265P and IGH PCR can also be used to diagnose Bing-Neel syndrome.

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2025
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