CSF

When determining an infection of the CNS it is necessary to differentiate between intrathecally produced antibodies and antibodies which have migrated from the blood into CSF. This is done by measuring the concentrations of pathogen-specific antibodies, corresponding immunoglobulin classes (total IgG, IgM) and albumin in both the CSF and serum of the patient. If an infection of the central nervous system is present, pathogen-specific antibodies accumulate in the CSF. If, however, the infection has not spread to the brain and the blood/ CSF barrier is still intact, the distribution of pathogen-specific antibodies in CSF and serum is the same as that of total IgG. The intrathecal pathogen-specific antibody production is defined by the relative CSF/serum quotient CSQrel. (synonym: antibody specificity index). The quotient is calculated from the amount of specific IgG antibodies in total CSF IgG in proportion to the amount of specific IgG antibodies in total serum IgG. A CSQrel. >1.5 indicates intrathecal synthesis of pathogen-specific antibodies.

In addition to the determination of specific antibodies, also the investigation of chemokine CXCL13 in CSF is useful for the diagnosis of neuroborreliosis. In patients with acute neuroborreliosis, in early stages of the disease, high concentrations of CXCL13 are frequently observed, often even before antibodies against Borrelia are detectable. CXCL13 determination can help to close the gap between infection and positive antibody test and to diagnose neuroborreliosis at an earlier stage. Moreover, CXCL13 used as activity marker helps to differentiate between acute and past neuroborreliosis. CXCL13 is also suitable as a marker for the disease course after treatment. Its concentration in CSF decreases with successful therapy. It needs to be taken into account that increased CXCL13 values can also be observed in other diseases, in particular in CNS lymphoma, HIV infections and neuro-lues.