QLTI-17. COMPARATIVE ANALYSIS OF LUMBAR PUNCTURE UTILITY IN DIAGNOSIS OF PRIMARY VERSUS SECONDARY CNS LYMPHOMA: A RETROSPECTIVE STUDY

Abstract OBJECTIVES Central nervous system lymphoma (CNSL) is a subtype of non-Hodgkin lymphoma, which affects the brain, spinal cord, leptomeninges, or eyes. It includes primary (PCNSL) and secondary CNSL (SCNSL). CNSL diagnosis relies on neuroimaging, cerebrospinal fluid (CSF) analysis (cytology, flow cytometry), and/or tissue biopsy. Lumbar punctures (LP) aid in investigating leptomeningeal involvement. Positive findings confirm CNS involvement and guide treatment decisions. This study seeks to determine the effectiveness of CSF analysis via LP in diagnosing SCNSL compared to PCNSL. METHODS This retrospective study comprised patients who received treatment with HD-MTX treated at our center from July 2020 to January 2024. Data was retrospectively collected from electronic medical records (EMR). Pathology reports from tissue biopsy and enhancement of CNS visualized on imaging were utilized to diagnose and differentiate PCNSL and SCNSL. CNS cytology and flow cytometry from LP were analyzed to determine the diagnostic accuracy of LP CSF cytology results in diagnosing CNSL. Descriptive statistical and comparative analysis was conducted to analyze the results. RESULTS The sample included 70 patients, 35 each diagnosed with PCNSL and SCNSL. Of these, only 49 patients underwent LP, with a significantly higher proportion of patients in the SCNSL group, 33 (67%), compared to the PCNSL group, 16 (33%) (P<0.001). Among those who underwent LP, CSF cytology and/or flow cytometry were positive in 19 cases, with significantly higher detection rates among the SCNSL cases (16 of 33, 48.5%) compared to the PCNSL cases (3 of 16, 18.8%; p=0.045). CONCLUSION Our findings indicate that LPs play a crucial role in diagnosing SCNSL, with a significantly higher CSF detection rate than PCNSL. LP has a limited impact on diagnosing PCNSL, suggesting that tissue biopsy should be prioritized to avoid increased time for PCNSL diagnosis. This study underscores the importance of tailored diagnostic approaches for suspected PCNSL and SCNSL, emphasizing the utility of LP in diagnosing SCNSL and tissue biopsy for PCNSL.