Beta-2-microglobulin levels in the cerebrospinal fluid of normal dogs and dogs with neurological disease

Background: Cerebrospinal fluid (CSF) analysis is the basis for establishing a diagnosis of central nervous system (CNS) inflammation. However, the information provided by routine CSF analysis is limited. Determination of CSF beta-2-microglobulin (beta(2)m) concentration has been used diagnostically in humans to identify inflammatory CNS disease; we hypothesized that it may have similar value in dogs. Objectives: The objective of this study was to measure beta(2)m concentration in the CSF of clinically healthy dogs and compare the values to those observed in dogs with inflammatory CNS disease and intervertebral disc disease (IVDD). Methods: CSF was collected from 10 clinically healthy laboratory dogs and 11 dogs each with inflammatory CNS disease and IVDD. Routine CSF analysis was performed, and beta(2)m concentration was measured by ELISA. CSF beta(2)m concentration and CSF: serum beta(2)m ratio were compared between groups by ANOVA. Linear relationships between CSF total nucleated cell count (TNCC), RBC count, total protein concentration, and beta(2)m concentration were assessed by regression analysis. Results: The mean (+/- SD) CSF beta(2)m concentration in clinically healthy dogs was 0.36 +/- 0.05 mu g/mL (cisternal) and 0.40 +/- 0.07 mu g/mL (lumbar). Median CSF beta(2)m concentration in dogs with IVDD (0.46 mu g/mL) and inflammatory CNS disease (0.85 mu g/mL) differed from that of controls (0.36 mu g/mL; P = .002). The concentration also differed between the 2 disease groups (P = .01). Five dogs with inflammatory CNS disease had CSF: serum beta(2)m ratios > 1. A correlation was identified between TNCC and beta(2)m concentration (r = 0.69, P = .0003). Conclusions: CSF beta(2)m concentration is higher in dogs with IVDD and inflammatory CNS disease, with highest values seen with inflammatory disease. This may be attributed in part to the correlation between CSF beta(2)m concentration and TNCC, but also may reflect intrathecal immune activation.