[Lyme borreliosis--diagnostic difficulties in interpreting serological results]

Lyme borreliosis is a multi-systemic disease caused by spirochete Borrelia burgdorferi sensu lato. The specific response is influenced by phenotypic characteristics of Borrelia, different antigen structure, their different geographic distribution, and the patient's capability to react to the infection. The immune response to Borrelia burgdorferi sensu lato develops relatively late, whereas in some patients it never develops. The immune response in the early phase of Lyme borreliosis is very similar to the one of healthy population.

Clinical manifestation, detailed anamnesis and epidemiological data are crucial for making the diagnosis. The majority of patients in the late phase of Lyme borreliosis have IgG antibody response, which could be followed by IgM also throughout this period of time. The number of serologically positive findings increases with the duration of the infection. Specific borrelial antigens can be detected by a Western blot test. In patients with neuroborreliosis, antibodies could be synthesized only intrathecally. IgG and IgM antibody response can persist for many years after the treatment. There is no positive serological test, which could be the indicator of the disease activity on its own; even if it demonstrates high antibody titre. If there are no clinical signs of Lyme borreliosis, the diagnosis of Lyme borreliosis should be primarily based on clinical findings, and serological results should be used only to confirm but not to make the diagnosis of Lyme borreliosis. Specific antibodies from the IgM class can be proved in about 50% of patients, 2 to 4 weeks after the onset of primary infection, but an early administration of the antibiotics can postpone or inhibit that response.

When interpreting the serological test results with high level of sensitivity and specificity used for making diagnosis of Lyme borreliosis, it is necessary to take into consideration the seroprevalence in a certain region. In the population with a low prevalence of the disease, the tests will have a low positive predicative value, i.e. the probability of indicating the real disease will be lower. According to the recommendations given by the Centre for Disease Control in North America, all extreme and positive results of EA and IFA are to be confirmed by a Western blot test.

The main problem in making diagnosis of Lyme borreliosis is underestimation and overrating of the diagnosis. Not a single positive serologic test is the indicator of the disease activity on its own, regardless of the antibodies titre level, when clear clinical signs are scarce.