AE is often diagnosed by the detection of specific antibodies against different neuronal surface antigens in the cerebrospinal fluid (CSF), the blood or both. However, the antibody testing usually takes several days. A group at Ulm University in Germany reviewed the basic CSF findings of 1,305 patients with the 10 most important AE subtypes, for the presence of pleocytosis, protein and oligoclonal bands (OCB), that might prove an inflammatory origin of neurological disturbances compatible with AE prior to the specific test results, thereby supporting the diagnosis and triggering early treatment.
Their results indicate that these basic CSF findings are greatly different among the 10 different AE subtypes. Whereas, AEs with antibodies against NMDA, GABAB, and AMPA receptors as well as DPPX show frequent inflammatory CSF changes, in AEs with either CASPR2, LGI1, GABAA, or glycine receptor antibodies CSF findings were mostly normal. In AE with GAD antibodies, positive OCBs in the absence of other changes were typical, while the CSF in IgLON5 antibody-positive AIE was characterized by elevated protein.
Thus, it can be expected that AEs with NMDAR, AMPAR, GABABR, and DPPX antibodies in most cases will show inflammatory CSF changes supporting the diagnosis of AE before the results of a specific antibody testing are available, but this will not be the case in most patients with LGI1, IgLON5, CASPR2, and GlyR antibodies.
The group concluded that non-paraneoplastic and IgG4 pre-dominant disease subtypes tend to have less CSF inflammatory activity compared to diseases with IgG1 pre-dominance, which more frequently are paraneoplastic. AE with NMDAR antibodies is the most frequent AE subtype at younger age and almost always associated with inflammatory CSF findings while anti-LGI1 AE, the most frequent AE subtype in the elderly, in the majority of patients CSF is normal. They conclude that in suspected AE in the elderly, normal basic CSF findings should not lead to the decision against testing for antineuronal antibodies.
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