Is there a relationship between CSF Interleukin 34 Level and clinicoradiological activity and IgG index in patients with MS?

•Interleukin −34 (IL34) levels in cerebrospinal fluid of patients with Multiple Sclerosis (MS) were not found to be a predictive feature of clinical and/or radiological activity in one-year follow-up after the diagnosis.•Significantly higher levels of IL-34 in cerebrospinal fluid in the patient group may support its role in the pathogenesis of MS.•The level of IL-34 in cerebrospinal fluid of MS patients may be a candidate biomarker expressing inflammatory response, similar to the IgG index. Multiple sclerosis is an autoimmune, inflammatory, and disabling disease that is subject to research, with the aspects of its pathogenesis awaiting clarification. It is essential to predict the prognosis of the disease and find the responsible mechanisms and molecules to become a treatment option. In this regard, researching the impact of Interleukin 34, with its immunomodulatory properties, on the clinicoradiological activity effect of MS and determining its role, if any, may be guiding. The study included 52 MS patients who underwent lumbar puncture at the diagnosis stage, and dimethyl fumarate treatment was initiated in these patients. During a one-year prospective follow-up, CSF IL-34 levels of 26 patients with clinical and/or radiological activity and 26 patients without activity were evaluated for prediction of disease activity. Additionally, CSF IL-34 levels of 26 control patients who underwent lumbar puncture due to pseudotumor cerebri but were not diagnosed with this disorder and whose CSF examinations were normal and were compared with MS patients. Our study also included the Immunoglobulin G index and investigated its relationship with IL-34. The IL-34 level was higher in the MS patient group compared to the control group. No significant difference was identified between MS patient groups with and without clinical and/or radiological activity. A weak correlation without statistical significance was found between IL-34 and the IgG index. The IL-34 level did not correlate with clinical and radiological activity in MS patients. However, the high IL-34 level observed in the patient group in comparison with the control group may be significant for MS pathogenesis. Furthermore, IL-34 may be a useful biomarker candidate for MS diagnosis, similar to the IgG index.