P14.04.A CHARACTERISTIC FEATURES OF PATIENTS WITH AUTOIMMUNE DIFFERENTIAL DIAGNOSES FOR PRIMARY CENTRAL NERVOUS SYSTEM LYMPHOMA (PCNSL)

Abstract BACKGROUND The diagnosis of this rare subtype of B-cell non-Hodgkin’s lymphoma limited to the CNS includes magnetic resonance imaging (MRI), tissue biopsy, cerebrospinal fluid (CSF) analysis and systemic staging. In imaging, PCNSL may resemble a number of differential diagnoses including autoimmune diseases like multiple sclerosis (MS). To identify aspects with which autoimmune differential diagnosis can be ruled out, we analyzed clinical and diagnostic features in PCNSL patients. MATERIAL AND METHODS Data of 107 patients who were hospitalized at University Hospital Regensburg and diagnosed with PCNSL between 2012 and 2022 were reviewed retrospectively. Patients were retrospectively classified according to the McDonald criteria of 2017, according to which MS is diagnosed. Descriptive statistics and correlation analyses, using Student’s T test, Chi-squared test and Fisher’s exact test, were performed. RESULTS Of 104 patients, to whom the McDonald criteria could be retrospectively applied, 6 (5.8%) patients with formally positive criteria were identified. Of these six patients, the majority (66.7% vs. 33.3%) had a relapsing symptomatology that could resemble MS (p < 0.001). Patients with positive McDonald criteria (n = 6) had significantly more often (50%) a history of an autoimmune disease (like Crohn’s disease or rheumatoid arthritis) compared to patients with negative McDonald criteria (4.1%) (p = 0.004). CSF-specific oligoclonal bands (OCBs) were detected in 60% (n = 3) of patients with positive McDonald criteria and in 8% (n = 4) of patients with negative criteria (p < 0.001). Regarding MRI criteria, patients with positive McDonald criteria had more often oval lesions (83.3%, n = 5 vs. 26.9%, n = 25) (p = 0.009). Furthermore, patients with positive McDonald criteria showed more often lesions in the cerebellum (33.3%, n = 2 vs. 2.0%, n = 2) (p = 0.021). Patients with negative McDonald criteria had their main lesions more often in the white matter (54.1%, n = 53 vs. 16.7%, n = 1) and both supra- and infratentorial (21.4%, n = 21 vs. 16.7%, n = 1) (p = 0.021). The distribution of periventricular lesions was surprisingly not significant (100%, n = 6 vs. 86.9%, n = 86) (p = 1.0). The same was demonstrated for multiple lesions (50%, n = 3 vs. 48%, n = 47) (p = 0.060). CONCLUSION In our study, very few patients with confirmed PCNSL had retrospectively positive McDonald criteria. Therefore, MS is an unlikely but in single cases highly relevant differential diagnosis for PCNSL, however other autoimmune diseases such as vasculitis can still be considered.. Autoimmune differential diagnoses should rather be considered if patients have an autoimmune disease in their medical history. Regarding diagnostics, CSF-specific OCBs or an oval or lumpy lesion on MRI might be suspicious for MS. In addition, frontal lesions may be less frequent among patients with MS as possible differential diagnosis.