2.2. Analysis of blood and cerebrospinal fluid

All samples from patients and controls were immediately transferred to the laboratory, were centrifuged at 4000 rpm for 10 minutes, and stored at −80°C until assayed. Chemokine and cytokine analysis was performed using a commercial bead-based multiplexed human cytokine assay analyzing 40-cytokines (BioRad BioPlex Pro Human Chemokine Assay, all are shown in Table ​Table1).1). Serum was diluted according to manufacturers' instructions, and CSF was diluted two-fold in sample dilution buffer. Analysis was performed on a Luminex 200 instrument (Luminex Corporation, Austin, TX). All analyses were performed in duplicates. Analysis included measurement of calibrators, controls, and standards.

Z-scores of chemokine and cytokine concentrations in serum and cerebrospinal fluid of patients with painful polyneuropathy compared with pain-free controls.

All values are depicted as mean ± SD. The calculation was based on the raw data. Patients' z-scores are shown in reference to the pain-free controls based on the following formula: z = (X_patient − Mean_controls)/SD_control. A z-score of “0” corresponds to the mean of pain-free controls, values >0 correspond to higher concentrations, <0 to lower concentrations.

Bold values show significances between patients with painful polyneuropathy and pain-free controls.

CSF, cerebrospinal fluid.