Cerebrospinal Fluid Cytology in Lyme Neuroborreliosis Revisited—Role of Neutrophilic Granulocytes: A Retrospective Single-Center Study

Background/Objectives: diagnosis of Lyme neuroborreliosis (LNB) relies on medical history, clinical findings, and detection of pathogen-specific antibodies in the blood and cerebrospinal fluid (CSF). The chemoattractant CXCL13 serves as an additional marker for LNB acuity. During the diagnostic workup, cytomorphological examination of immune cells in CSF provides early insights. Lympho-monocytic pleocytosis with plasma cells and activated lymphocytes is usually described as a typical feature of LNB. In contrast we frequently observe a cytological cell picture featuring neutrophilic granulocytes as well as activated mononuclear cells and plasma cells in patients with LNB, which we refer to as a mixed cell picture. We, hence, investigated the presence of granulocytes to determine their role as typical findings associated with LNB. Methods: we conducted a retrospective analysis of CSF cytology in patients diagnosed with definite LNB at the Department of Neurology, Christian Doppler Medical Centre, Salzburg between 2015 and 2021. CSF results of patients with more than 10 erythrocytes/µL were excluded to avoid the presence of granulocytes due to artificial blood contamination. Additionally, CXCL13 levels were recorded, where available. Results: a total of 75 patients (42 female; 56%) met the diagnostic criteria of definite LNB. Cytology revealed the presence of granulocytes in the CSF of 91% of the patients (68/75). CXCL13 elevation was found to be significantly associated with the presence of granulocytes in CSF (p = 0.0025, or 1.009 (95% CI: 1.003–1.016). Conclusions: we confirm a mixed cell picture with granulocytes, activated mononuclear cells and plasma cells being a typical finding in the CSF cytology of LNB. The association between granulocytes and elevated CXCL13 suggests that their presence is a specific feature of the acute, untreated phase of LNB.