The aim of our study was to introduce the specific antibody index (AI) and to determine intrathecal synthesis of specific antiborrelia antibodies in clinical and laboratory practice in the Czech Republic with regard to the endemic variability of infectious agents. We considered additional laboratory parameters of investigated CSF and blood samples to reveal the value of AI in relation to various clinical phases of neuroborreliosis. Methods: We investigated a cohort of 10 patients with positive titres of antiborrelia IgG antibodies in CSF and/or clinical symptoms of neuroborreliosis. 3 patients with negative titres of antiborrelia antibodies and without clinical symptoms of neuroborreliosis served as negative controls. Antiborrelia IgG antibodies were measured by immunoenzymatic method (EIA Borrelia afzelii IgG). Concentrations of albumin and IgG were measured by nephelometry. The absolute values of absorbances of serum and CSF were converted to arbitrary units (AU) and the antibody index (AI) value was calculated according to Reiber’s formula. In parallel we investigated the additional parameters in CSF, i.e. albumin quotient (Qalb), cytology and oligoclonal IgG bands. Results: 7 patients had positive values of the specific Borrelia antibody index – AI in the range 1.66–33. 4 of them had symptoms of acute neuroborreliosis with pleocytosis and impaired blood-CSF barrier. Another 3 patients with normal CSF cytology and blood-CSF barrier had a positive specific AI and according to anam- nestic and clinical data were considered as neuroborreliosis in the ease-history. 3 patients with positive titres of specific IgG in CSF and disturbances of blood-CSF barrier had negative AI. 3 patients who served as negative controls were negative in all followed parameters with the exception of oligoclonal band positivity in a patient with multiple sclerosis. Conclusion: The specific antibody index (Bb-IgG-AI) is of high significance for diagnosis of neuroborreliosis especially in the context of additional CSF parameters.

        Key words: neuroborreliosis, Borrelia burgdorferi, specific IgG antibody index.