The European Federation of Neurological Societies (EFNS) established guidelines for LNB diagnosis in 2010 [
10]. The criteria for LNB diagnosis are: LNB compatible neurological symptoms and signs with no other explanation, pleocytosis and production of
Bb specific antibodies in the cerebrospinal fluid (CSF). Intrathecal antibody production is often expressed as a positive
Bb antibody index (AI), where measurements of antibody show a higher level in CSF than in serum [
14]. The European guidelines state that the condition is possible when two out of three criteria are present, and definite when all three criteria are met (Table
1). Direct test methods for detection of
Bb, mainly culture and polymerase chain reaction, have low sensitivity and are seldom helpful in the diagnostic work-up [
14]. Interpretation of serology can also be a challenge in the diagnostic process, since the sensitivity is low in the early stage of infection. Further, both IgM and IgG antibodies can remain positive several years after infection, so results may not differentiate previous exposure, reinfection or acute infection [
14,
15]. American Academy of Neurology (AAN) diagnostic criteria do not include analysis of cerebrospinal fluid, but presence of one or more of erythema migrans, direct proof through histopathology, microbiology or polymerase chain reaction or immunologic evidence of infection [
4]. To increase specificity of serology, a two-tier approach is recommended with an initial enzyme immunoassay followed by separate immunoglobulin Western blots if the first step is positive [
14]. Both American and European diagnostic criteria for LNB emphasise the exclusion of other apparent cause to the clinical disorder [
4]. Magnetic resonance imaging (MRI) therefore makes a crucial contribution in the diagnosis and follow-up of LNB.
Table 1
EFNS diagnostic criteria for LNB
a [
10]
1) Neurological symptoms suggestive of LNB without other obvious reasons 2) Cerebrospinal fluid pleocytosisb 3) Intrathecal Bb antibody production | All three criteria fulfilled | Clinical criteria and one of two laboratory criteria fulfilled |