Lyme borreliosis should be considered in patients with cranial nerve palsy, in particular, seventh nerve palsy, and signs of meningitis with or without headache, lethargy, or irritability for about 9 days on average before admission [
25,
27]. Stiffness of the neck is often very mild or absent and must be searched for carefully. In contrast, patients with aseptic/viral meningitis usually display obvious nuchal rigidity and have a history of less than 6 days, often 1 or 2 days only [
4,
27]. Especially in the absence of cranial nerve palsy, the possible diagnosis of Lyme borreliosis is not being considered often enough. Patients with headache as a sole manifestation usually do not have neuroborreliosis. In comparison to patients with noninflammatory headaches of frequent and various causes, the headaches of patients with neuroborreliosis usually have a clearly indicated beginning and a short duration of less than a month [
27]. To confirm neuroborreliosis, antibodies against
Borrelia burgdorferi are assessed in serum and cerebrospinal fluid. In the case of early neuroborreliosis, there is lymphocytic pleocytosis in the cerebrospinal fluid, but often, intrathecal antibody production cannot yet be found [
24]. If cerebrospinal fluid yields pleocytosis with ≥90 % mononuclear cells, there are no other remaining causes apart from tuberculous meningitis. In very early stages of the disease, serological results in serum may still be negative [
4]. In typical cases, antibodies of the immunoglobulin IgM class against
B.
burgdorferi are found by enzyme immunoassay and are confirmed by two or more bands by IgM immunoblot. Later, IgG antibodies may be detected by enzyme immunoassay, and the number of bands in the IgG immunoblot increases gradually. Therefore, in case of a negative serology and continuing suspicion of neuroborreliosis, it may be useful to determine antibodies in serum again 2 or 3 or 4 weeks later to find seroconversion. PCR in cerebrospinal fluid often is positive only in very early cases when there are not yet antibodies against
B.
burgdorferi present. Although a positive PCR supports the diagnosis of neuroborreliosis, a negative PCR does not exclude it [
18]. Therefore, PCR should not be used routinely to make a diagnosis of neuroborreliosis, but only in complex cases.