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H-intensity scale score to estimate CSF GluN1 antibody titers with one-time immunostaining using a commercial assay
Masaki Iizuka1, Naomi Nagata1, Naomi Kanazawa1
1Department of Neurology, Kitasato University School of Medicine, Sagamihara, Japan.
Insights
A new H-intensity scale (HIS) score helps estimate anti-NMDA receptor encephalitis severity using cerebrospinal fluid (CSF) autoantibody (ab) titers. Higher HIS scores correlate with severe symptoms and poorer functional status at one year.
Area of Science:
- Neuroimmunology
- Autoimmune Encephalitis
- Antibody Titration
Background:
- Anti-NMDA receptor encephalitis involves autoantibodies (abs) targeting GluN1 subunits.
- Commercial cell-based assays (CBAs) are used, but the clinical significance of ab titers is unclear.
- A novel H-intensity scale (HIS) was developed to quantify GluN1-abs in CSF.
Purpose of the Study:
- To develop and validate an H-intensity scale (HIS) score for estimating GluN1-ab titers in CSF.
- To assess the clinical significance of HIS scores in patients with suspected autoimmune encephalitis.
- To correlate HIS scores with clinical and paraclinical features of the disease.
Main Methods:
- Compared commercial CBA with an established assay in 370 patients.
- Created positive control panels using serial dilutions of high-titer CSF.
- Scored ab reactivity in 79 patients' CSF using a 0-6 scale and assessed inter-assay reliability.
Main Results:
- CBA demonstrated high sensitivity (93.7%) and specificity (98.6%).
- Higher HIS scores were associated with typical disease spectrum, mechanical ventilation, autonomic dysfunction, dyskinesias, and altered consciousness.
- HIS score at diagnosis significantly impacted 1-year functional status.
Conclusions:
- The HIS score effectively estimates CSF GluN1-ab titers and correlates with disease severity.
- Higher GluN1-ab titers are linked to more severe symptoms and poorer long-term outcomes.
- Incomplete phenotypes may be associated with lower CSF GluN1-ab titers.
Introduction:
Anti-NMDA receptor encephalitis is an autoimmune disorder caused by autoantibodies (abs) against the conformational epitope on GluN1 subunits. GluN1-abs have been determined with cell-based assay (CBA) co-expressing GluN1/GluN2 subunits. However, commercial fixed CBA expressing only GluN1 subunit has increasingly been used in clinical practice. The ab titers can be determined with serial dilutions, but its clinical significance remains unclear. We aimed to develop an H-intensity scale (HIS) score to estimate GluN1-ab titers in cerebrospinal fluid (CSF) with one-time immunostaining using both commercial CBA and immunohistochemistry and report its usefulness. "H" is the initial of a patient with high CSF GluN1-ab titers (1:2,048).
Methods:
We first determined the reliability of CBA in 370 patients with suspected autoimmune encephalitis by comparing the results between commercial CBA and established assay in Dalmau's Lab. Then, we made positive control panels using the patient H's CSF diluted in a fourfold serial dilution method (1:2, 1:8, 1:32, 1:128, 1:512, and 1:2,048). Based on the panels, we scored the intensity of ab reactivity of 79 GluN1-ab-positive patients' CSF (diluted at 1:2) on a scale from 0 to 6 (with ≥1 considered positive). To assess inter-assay reliability, we performed immunostaining twice in 21 patients' CSF. We investigated an association between the score of CSF obtained at diagnosis and the clinical/paraclinical features.
Results:
The sensitivity and specificity of CBA were 93.7% (95% CI: 86.0-97.3) and 98.6% (95% CI: 96.5-99.5), respectively. Linear regression analysis showed a good agreement between the scores of the first and second assays. Patients with a typical spectrum, need for mechanical ventilation support, autonomic symptoms/central hypoventilation, dyskinesias, speech dysfunction, decreased level of consciousness, preceding headache, ovarian teratoma, and CSF leukocyte count >20 cells/µL had a higher median HIS score than those without, but HIS score was not associated with sex, age at onset, or seizure. HIS score at diagnosis had a significant effect on 1-year functional status.
Discussion:
The severity of disease and four of the six core symptoms were associated with higher GluN1-ab titers in CSF at diagnosis, which may play a role in poor 1-year functional status. An incomplete phenotype can be attributed to low CSF GluN1-ab titers.
