Limitations of a Commercial Assay as Diagnostic Test of Autoimmune Encephalitis

Abstract

Detection of neuronal surface antibodies (NSAb) is important for the diagnosis of autoimmune encephalitis (AE). Although most clinical laboratories use a commercial diagnostic kit (Euroimmun, Lübeck, Germany) based on indirect immunofluorescence on transfected cells (IIFA), clinical experience suggests diagnostic limitations. Here, we assessed the performance of the commercial IIFA in serum and CSF samples of patients with suspected AE previously examined by rat brain immunohistochemistry (Cohort A). Of 6213 samples, 404 (6.5%) showed brain immunostaining suggestive of NSAb: 163 (40%) were positive by commercial IIFA and 241 (60%) were negative. When these 241 samples were re-assessed with in-house IIFA, 42 (18%) were positive: 21 (9%) had NSAb against antigens not included in the commercial IIFA and the other 21 (9%) had NSAb against antigens included in the commercial kit (false negative results). False negative results occurred more frequently with CSF (29% vs 10% in serum) and predominantly affected GABABR (39%), LGI1 (17%) and AMPAR (11%) antibodies. Results were reproduced in a separate cohort (B) of 54 AE patients with LGI1, GABABR or AMPAR antibodies in CSF which were missed in 30% by commercial IIFA. Patients with discordant GABABR antibody results (positive in-house but negative commercial IIFA) were less likely to develop full-blown clinical syndrome; no significant clinical differences were noted for the other antibodies. Overall, NSAb testing by commercial IIFA led to false negative results in a substantial number of patients, mainly those affected by anti-LG1, GABABR or AMPAR encephalitis. If these disorders are suspected and commercial IIFA is negative, more comprehensive antibody studies are recommended.

CSF Biomarkers in COVID-19 Associated Encephalopathy and Encephalitis Predict Long-Term Outcome

“…The detection of neural antibodies (against neuronal surface antigens and onconeural antigens) was performed by tissue immunohistochemistry, as previously described ( 11 ). Samples that produced a neuropil or intraneuronal immunostaining on rat brain immunohistochemistry were subsequently examined with Indirect Immunofluorescence assay (IIFA) or Immunoblot, respectively, as previously described ( 12 ). CSF samples of patients with encephalitis were tested for SARS-CoV-2 by RT-PCR.…”

Autoimmune Encephalitis and Other Neurological Syndromes With Rare Neuronal Surface Antibodies in Children: A Systematic Literature Review

“…Therefore, CBAs with live or fixed eukaryotic cells to express the protein at the cell surface in its “physiological” state are the most used assays for NSAbs ( 72 – 74 ), and live CBAs are the gold standard in MOGAD ( 75 ). Commercial CBAs are generally used in clinical practice but antibody detection is improved by pairing with in-house diagnostics (immunohistochemistry, live CBAs, and neuronal cultures), although this may be challenging to implement in laboratories that lack the required expertise, and is therefore not always available ( 73 , 76 – 79 ). Moreover, commercial CBAs do not cover all NSAbs (i.e., GABAR, GlyR, D2R, and neurexin-3alpha), posing an additional challenge in the identification of these rare NSAS.…”

Novel qEEG Biomarker to Distinguish Anti-NMDAR Encephalitis From Other Types of Autoimmune Encephalitis

“…Our study agrees with others in that the proportion of AE encephalitis was 26% (23/90), of which NMDARE accounted for 39% (9/23) of AE. Recent studies also recommend diagnosing AE by immunolabeling with the rat brain tissue (tissue-based assay: TBA) and/or culturing live primary neurons to screen a series of neuronal surface antibodies (NSAs) in patients’ CSF and serum ( 15 , 16 ). Accordingly, we analyzed all 90 paired samples (both CSF and serum) by using in-house screening assays; 11 positive patients, whose samples produced neuropil immunostaining on TBA and detected immunofluorolabeled neurons on Live-neuron assay, were then classified into nine NMDARE, of whom two (cases 5 and 6 in other AEs) screened positives without detection of the 7 types of commercially available antigens on the cell-based assay ( Supplementary Table 1 ).…”