CSF Findings in Acute NMDAR and LGI1 Antibody-Associated Autoimmune Encephalitis

Abstract

Background and objectives: CSF in antibody-defined autoimmune encephalitis (AE) subtypes shows subtype-dependent degrees of inflammation ranging from rare and often mild to frequent and often robust. AEs with NMDA receptor antibodies (NMDAR-E) and leucine-rich glioma-inactivated protein 1 antibodies (LGI1-E) represent opposite ends of this spectrum: NMDAR-E with typically frequent/robust and LGI1-E with rare/mild CSF inflammation. For a more in-depth analysis, we characterized CSF findings in acute, therapy-naive NMDAR-E and LGI1-E in a multicentric, retrospective, cross-sectional setting.

Methods: Eighty-two patients with NMDAR-E and 36 patients with LGI1-E from the GErman NEtwork for Research of AuToimmune Encephalitis (GENERATE) with lumbar puncture within 90 days of onset and before immunotherapy were included. CSF parameters comprised leukocytes, oligoclonal bands (OCBs), and CSF/serum ratios for albumin, immunoglobulin G (IgG), A (IgA), and M (IgM), the latter 3 converted to Z scores according to Reiber formulas. The MRZ reaction was tested in 14 patients with NMDAR-E and 6 patients with LGI1-E, respectively.

Results: CSF was abnormal in 94% of NMDAR-E but only in 36% of LGI1-E patients. Robust quantitative intrathecal immunoglobulin synthesis (IIS, IgG > IgM >> IgA) was characteristic for NMDAR-E, but absent in LGI-E. In NMDAR-E, CSF leukocytes were higher when IIS was present or more pronounced. In addition, in NMDAR-E, CSF leukocytes were lower and IIS occurred less often and if so to a lesser degree at older age. Patients with NMDAR-E with severe functional impairment more often had positive OCBs. In CSF obtained later than 3 weeks of onset, leukocytes were lower. In parallel, the correlation of leukocytes with IIS disappeared as IIS was partially independent of disease duration. The MRZ reaction was positive in 5 (36%) patients with NMDAR-E. All these associations were completely absent in LGI1-E. Here, younger patients showed more blood-CSF barrier dysfunction. In LGI1-E, but not in NMDAR-E, the blood-CSF barrier was more dysfunctional when CSF leukocytes were higher.

Discussion: NMDAR-E and LGI-E differ in their typical extent of CSF inflammation. In addition, the patterns formed by the different inflammatory CSF parameters and their relationship with disease severity, age, and disease duration are subtype-characteristic. Moreover, signs for multiple sclerosis-like chronic inflammation are present in a subgroup of patients with NMDAR-E. These CSF patterns might be markers for the different immunopathogeneses of LGI1-E and NMDAR-E.

Figure 1. Study Profile

Flowchart depicting the enrollment process. AE = autoimmune encephalitis; HSVE = herpes simplex virus encephalitis; AB = antibody.

Figure 2. CSF Findings Are Very Different in NMDAR-E Compared With LG1-E

In 82 and 36 patients with therapy-naive NMDAR- and LGI1-E undergoing lumbar puncture within 90 days after onset of symptoms, basic CSF findings, cell count (A), age-adjusted blood-CSF barrier function (Q_Alb/Q_lim, B), and the presence of isolated oligoclonal bands (OCB) in CSF as most sensitive proof for intrathecal IgG synthesis (C) were compared. (A) CSF leukocytes counts were logarithmized after adding 1, thus Ln(cell count +1) in patients with 0 cells/µL is 0. (B) The individual CSF/serum albumin ratio (Q_Alb) was normalized by division with the age-dependent upper limit [Q_lim, 4 + age (yrs)/15]. (D) CSF/serum IgG, IgA, and IgM ratios (Q_IgG, Q_IgA, and Q_IgM) were compared with the expected mean CSF/serum ratio with regard to the individual Q_Alb calculated by the Reiber formulas (traditional Reiber diagrams can be found in eFigure 4, links.lww.com/NXI/A600). The distance from the mean Q_Ig is expressed as the number of standard deviations (Z score), with a Z score >3 judged as a proof of intrathecal synthesis (black), a Z score ≤3 but >2 classified a probable intrathecal synthesis (dark gray), and a Z score ≤2 but >1 classified a possible intrathecal synthesis (light gray). The resulting Z scores were logarithmized after adding the correction factor c (2.51), resulting in Ln(zQ_Ig + c) of 0 in the patient with LGI1-E with the lowest Z score for Q_IgA (additional information in eFigures 1 and 2, links.lww.com/NXI/A600). (D) Comparison of the quantitative intrathecal IgG, IgA, and IgM synthesis in patients with NMDAR-E with patients with LGI1-E. (E) Frequency of intrathecal IgG, IgA, and IgM synthesis classified as present, probable, possible, or absent in both groups of patients. (F) Detection of a polyspecific immune activation using 3 pathogen-specific AIs for measles, rubella, and varicella zoster virus in a subset of patients with NMDAR-E (N = 14) and LGI-E (N = 6). Two elevated AIs (>1.4): dark gray, 1 elevated AI: light gray, no elevated AI: clear. The upper normal limits (lim, A: 4 leukocytes/µL, B: Q_Alb/Q_lim = 1.0, D: Q_mean + 3 SD) are indicated as dashed lines. Statistical analysis was performed using the Mann-Whitney U test (A/B, left panels, D) and Fisher exact test of the unnormalized number of patients (A/B, right panel, C/E). ns = not significant, **p < 0.01, and ****p < 0.0001 (additional analyses in eFigures 5 and 7–11, links.lww.com/NXI/A600). AI = antibody index; LGI1-E = leucine-rich glioma-inactivated protein 1; NMDAR-E = NMDA receptor.

Figure 3. In NMDAR-E, Quantitative Intrathecal Immunoglobulin Synthesis IIS Is Largely Independent of Disease Duration, Whereas CSF Leukocytes Are Higher Early After Clinical Onset

The 82 and 36 patients with therapy-naive NMDAR-E and LGI-E, respectively, were categorized with respect to the delay of lumbar puncture after onset of symptoms (week 1 = day 0–6; weeks 1/3 = day 7–20; ≥4 = day 21 and later). CSF leukocyte count, blood-CSF barrier function, and the presence of OCB are depicted as in Figure 2, A–C and quantitative intrathecal IgG, IgA, and IgM synthesis as in Figure 3, A and B. The upper normal limits (lim, cell count: 4 cells/µL, Q_Alb/Q_lim: 1.0, Q_Ig: Q_mean + 3 SD/Z score = 3, lim) are indicated as dashed lines. Statistical analysis was performed using the Kruskal-Wallis test followed by the Dunn multiple comparisons test (A/B/D), the χ² test of the unnormalized number of patients with and without OCB (C), or with or without intrathecal immunoglobulin synthesis of a Z score >3. ns = not significant and *p < 0.05 (additional analyses in eFigures 12–14, links.lww.com/NXI/A600). IIS = immunoglobulin synthesis; LGI1-E = leucine-rich glioma-inactivated protein 1; NMDAR-E = NMDA receptor.

Figure 4. With Increasing Age, Patients With NMDAR-E Become Less Likely to Show CSF Pleocytosis and Quantitative Intrathecal Immunoglobulin Synthesis, Whereas Blood-CSF Barrier Dysfunction Occurs More Frequently

Patients with NMDAR-E were divided into 3 groups, those with the age of 20 years or younger (≤20 years), those older than 40 years (>40 years), and those in between (21–40 years). CSF leukocyte count and frequency of pleocytosis (A), blood-CSF barrier function (B), and the presence of OCB restricted to the CSF (C) are presented as in Figure 2, A–C, but only for NMDAR-E, intrathecal IgG, IgA, and IgM synthesis (D) IIS presented as in Figure 3D. Statistical analysis was performed using the Kruskal-Wallis test followed by the Dunn multiple comparisons test (A/B/D, left panels). For intrathecal immunoglobulin synthesis, patients with a Z score >3 were compared with those ≤3. When comparing all 3 groups (B, right panel, C, D right panel IgG and IgM), the χ² test of the unnormalized number of patients was performed. If the criteria for a valid χ² test were not met, 2 groups were combined, and a Fisher exact test was performed (A, right panel, D right panel—IgA). ns = not significant, *p < 0.05, **p < 0.01, and ***p<0.001 (additional analyses including age dependency of CSF findings in LGI-E can be found in eFigures 15–18, links.lww.com/NXI/A600). NMDAR-E = NMDA receptor.

Figure 5. In NMDAR-E, the Presence of CSF-Specific OCBs and Increased Quantitative IIS for IgG, IgA, and IgM Are the Only CSF Finding Associated With Disease Severity at the Time Point of Lumbar Puncture

Patients with NMDAR-E and LGI1-E were dichotomized according to the degree of functional impairment using the mRS, with a score of 0–2 regarded as a low degree of impairment and 3–6 as a high degree of impairment (6 = death did not occur before lumbar puncture, eFigure 19, links.lww.com/NXI/A600). CSF leukocyte count and frequency of pleocytosis (A), age-adjusted blood-CSF barrier function (Q_Alb/Q_lim) (B), frequency of OCBs restricted to the CSF (C), and the probability of quantitative intrathecal immunoglobulin synthesis (D) are presented as in Figure 2, A–C for A-C and in Figure 3, A and B for D. Statistical analysis was performed using the Mann-Whitney U test (A/B/D, left panels) and the Fisher exact test (A/B/D right panels). For intrathecal immunoglobulin synthesis, patients with a Z score >3 were compared with those ≤3. ns = not significant, *p < 0.05, and **p<0.01 (additional analyses can be found in eFigure 19, links.lww.com/NXI/A600). LGI1-E = leucine-rich glioma-inactivated protein 1; mRS = modified Rankin Scale; NMDAR-E = NMDA receptor.

Figure 6. Comprehensive Summary of Results Shows the Profound Differences in the Interdependency of Inflammatory CSF Parameters Among Each Other and Clinically Overt Disease Duration, Age at Onset, and Disease Severity in NMDAR-E and LGI1-E

Graphical summary of all analyses. Details of the multiple analyses can be found in eTables 2–6, links.lww.com/NXI/A600. Results of the univariate (upper right halves) and multiple analyses (lower left halves) for (A) NMDAR-E and (B) LGI1-E. The variables are indicated at the top or left of the graphs. Age = age at LP; Time = time from clinical onset to LP; Cells = CSF leukocyte count; Q_Alb = CSF/serum albumin ratio; zIgG/A/M = z scores for IgG/A/M as a marker for quantitative intrathecal immunoglobulin synthesis. Each square summarized the results of the interaction of the 2 variables, which are color coded as indicated. Positive associations indicate significant results in at least 1 univariate analysis and a p < 0.05 in the multiple models. Putative associations were defined either as significant results with questionable relevance (LGI1-E: age vs zIgA in the absence of relevant quantitative synthesis of IgA) or as comparisons with p values <0.1 but not p < 0.05. (C) Synopsis of the results of combined univariate and multiple analyses for NMDAR-E (upper right half) and LGI1-E (lower left half). Color-coded results of the univariate analysis can be found as the uppermost and third stripe in each box for NMDAR-E and the left and third from the left strip in each box for LGI1-E. Boxes comparing 1 variable with itself are blackened. Comparison of the 3 confounders with each other or the different CSF parameters are indicated by 2 black frames. LGI1-E = leucine-rich glioma-inactivated protein 1; LP = lumbar puncture; mRS = modified Rankin Scale score at LP; NMDAR-E = NMDA receptor; OCB = oligoclonal bands restricted to the CSF.