Immunotherapies for Anti-NMDA Receptor Encephalitis: Multicenter Retrospective Pediatric Cohort Study in China


 BackgroundAnti-N-methyl-D-aspartate receptor (NMDAR) encephalitis has been discovered and termed more than a decade, but the establishment of standardized immunotherapy protocol for pediatric patients still needs more clinical evidence. To help move this forward, we investigated the current status of immunotherapies for pediatric anti-NMDAR encephalitis in 6 tertiary medical centers across China and evaluated how different immunotherapy strategies affected patient outcomes.MethodsA multicenter, retrospective study was conducted on pediatric patients diagnosed with anti-NMDAR encephalitis between November 2011 and December 2018. The clinical records including clinical manifestations, immunotherapy strategies, and outcomes were collected and analyzed. Treatment response and outcome were evaluated using mRS. Outcomes among the treatment groups were analyzed with the Chi-squared test or Fisher’s exact test. p < 0.05 was considered significant.ResultsA total of 386 patients were included in our study and the median onset age was 7.89 (range 0.5-18) years. All patients received first-line immunotherapy and the majority (341, 88.3%) used the standard combination of methylprednisolone pulses and intravenous immunoglobulins, but 211 patients did not show satisfactory improvement (mRS ≥ 3). Mainly three treatment strategies were applied after first-line immunotherapy: second-line immunotherapy, repetitive first-line immunotherapy, and maintaining oral prednisolone. For patients with mRS ≥ 4 after first-line immunotherapy, the incidence of poor outcome (mRS ≥ 3) in oral prednisolone group was higher than that in other treatment groups (0.025 < p < 0.05). No difference in complete recovery rate (mRS = 0) was found between patients receiving second-line and repetitive first-line immunotherapy, or patients using long-term and short-term prednisolone. The relapse rate of oral prednisolone group was higher than that of other treatment groups (p < 0.01), but the relapse rate of patients using long-term and short-term prednisolone had no statistical difference. ConclusionsFor patients with mRS ≥ 4 after first-line immunotherapy, second-line immunotherapy is recommended. When second-line immunotherapy is not applicable, repetitive first-line immunotherapy can be considered as an option. Both second-line and repetitive first-line immunotherapy are beneficial to reduce relapse rate. The duration of sequential oral prednisolone can be shortened after fully evaluating patients’ conditions.

encephalitis between November 2011 and December 2018. The clinical records including clinical manifestations, immunotherapy strategies, and outcomes were collected and analyzed. Treatment response and outcome were evaluated using mRS. Outcomes among the treatment groups were analyzed with the Chi-squared test or Fisher's exact test. p < 0.05 was considered signi cant.

Results
A total of 386 patients were included in our study and the median onset age was 7.89 (range 0.5-18) years. All patients received rst-line immunotherapy and the majority (341, 88.3%) used the standard combination of methylprednisolone pulses and intravenous immunoglobulins, but 211 patients did not show satisfactory improvement (mRS ≥ 3). Mainly three treatment strategies were applied after rst-line immunotherapy: second-line immunotherapy, repetitive rst-line immunotherapy, and maintaining oral prednisolone. For patients with mRS ≥ 4 after rst-line immunotherapy, the incidence of poor outcome (mRS ≥ 3) in oral prednisolone group was higher than that in other treatment groups (0.025 < p < 0.05). No difference in complete recovery rate (mRS = 0) was found between patients receiving second-line and repetitive rst-line immunotherapy, or patients using long-term and short-term prednisolone. The relapse rate of oral prednisolone group was higher than that of other treatment groups (p < 0.01), but the relapse rate of patients using long-term and short-term prednisolone had no statistical difference.

Conclusions
For patients with mRS ≥ 4 after rst-line immunotherapy, second-line immunotherapy is recommended. When second-line immunotherapy is not applicable, repetitive rst-line immunotherapy can be considered as an option. Both second-line and repetitive rst-line immunotherapy are bene cial to reduce relapse rate. The duration of sequential oral prednisolone can be shortened after fully evaluating patients' conditions. Background Page 4/15 Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis was rst termed in 2007 due to the discovery of speci c autoantibodies to NMDA receptors in a series of patients who developed a constellation of neuropsychiatric symptoms, associated with ovarian teratoma (1,2).
A large series study of 577 patients revealed approximately 80% of patients improved or recovered after immunotherapies and tumor removal if it was applicable (3). Compared to adult patients, pediatric patients showed a different clinical symptom pro le and lower tumor association rate, and they may have different response to immunotherapy and better outcome (4). Although the frame of immunotherapy is well de ned, in which, patients receive rst-line immunotherapy and then proceed to second-line immunotherapy if clinical improvement is not satisfactory, the evidence of effectiveness and superiority of any treatment regimen is lacking. Currently, the most widely accepted rst-line immunotherapy is the high-dose intravenous methylprednisolone pulses (MEP) alone or combined with intravenous immunoglobulins (IVIG); rituximab for second-line immunotherapy is another area of agreement (5,6). However, our survey on treatment strategies of pediatric neurologists in China revealed, a considerable proportion of clinical practitioners would repeat rst-line immunotherapy once before considering second-line immunotherapy (7). The survey of Bartolini et al. also showed pediatric neurologists were more likely to repeat rst-line immunotherapy compared to adult neurologists and pediatric rheumatologists (5). Furthermore, high dose of oral prednisolone followed by tapering is another major maintenance treatment after rst-line immunotherapy, but the dosage and duration are also open to discussion.
How these clinical decisions will affect the outcome of patients is still a pending question. Consequently, we performed this nationwide, multicenter study with 386 pediatric patients involved, aiming to investigate the current immunotherapy strategies for pediatric patients with anti-NMDAR encephalitis in China, and whether different immunotherapies affect the long-term prognosis or not. The average duration of follow-up in our study reached to 39.2 (range 12-91.9) months. Five (1.3%) patients were lost to follow-up. We were able to assess the nal mRS in 381 (98.7%) patients, and 360 (94.5%) achieved good outcome (mRS ≤ 2) including 270 patients had complete recovery (mRS = 0). By the last follow-up, 21 (5.4%) patients had poor outcome (mRS ≥ 3) and 6 (1.6%) of them died of this disease. The comparison of baseline characteristics of patients with good and poor outcome was shown in Table 1. The patients with poor outcome were more likely to be younger, have prodromal symptoms, especially fever within 3 weeks before onset, and have higher mRS at symptom onset. During the disease course, the patients with poor outcome were more likely to develop decreased level of consciousness, have abnormal brain MRI, and have unsatisfactory response to rst-line immunotherapy. Pediatric intensive care unit (PICU) admission was also more frequently required in the patients with poor outcome. There were mainly 3 treatment strategies after rst-line immunotherapy: second-line immunotherapy, repetitive rst-line immunotherapy, and maintaining oral prednisolone.

Study design
We grouped patients according to the response to rst-line immunotherapy and summarized their treatments.
In Outcome First, we analyzed whether mRS at symptom onset and after rst-line immunotherapy was relevant to the outcome of patients within each treatment group (Table 2) and found no difference in complete recovery rate between patients with mRS ≤ 3 and mRS ≥ 4 at symptom onset. However, in the treatment groups of second-line immunotherapy (0.025 < p < 0.05) and oral prednisolone (p < 0.005), the complete recovery rate of patients with mRS ≥ 4 after rst-line immunotherapy was lower than that of patients with mRS ≤ 3. Therefore, we classi ed patients based on their response to rst-line immunotherapy and analyzed the effects of different treatment strategies on patient outcome. For patients with mRS ≥ 4 after rst-line immunotherapy, the incidence of poor outcome in oral prednisolone group was higher than that in other treatment groups (Table 3, χ2 = 4.26, 0.025 < p < 0.05). In the groups of mRS = 3 and ≤ 2, there was no signi cant difference in outcome between patients from oral prednisolone group and other treatment groups (Table 3). Patients using long-term (> 3 months) and short-term (≤ 3 months) prednisolone showed no difference in complete recovery rate (Table 4). Moreover, patients receiving second-line, repetitive rst-line immunotherapy had no difference in complete recovery rate (Table 5). It is worth noting that in the group of mRS ≥ 4, 15 of 40 patients who repeated rst-line immunotherapy had to receive second-line immunotherapy due to poor improvement, but this subset of patients showed no difference in complete recovery rate compared to patients from other treatment groups.
During the follow-up, 27 (7%) patients relapsed and 25 (92.59%) of them were from the group of maintaining oral prednisolone.
The relapse rate of patients with oral prednisolone was higher than patients of other treatment groups (Table 6, χ 2 = 7.26, p < 0.01). But patients using long-term and short-term prednisolone showed no signi cant difference in relapse rate.    Repetitive rst-line immunotherapy 9 8 requirements and concerns about side effects, have to be taken into consideration when applying secondline immunotherapy.
In mRS ≥ 4 group, patients taking oral prednisolone showed unfavorable outcome compared to patients receive other treatments. Therefore, for patients with mRS ≥ 4 after rst-line immunotherapy, aggressive treatments are recommended and use of oral prednisolone without any other treatments should be avoided. Patients using second-line and repetitive rst-line immunotherapy did not show signi cant difference in complete recovery rate and 37.5% of patients who repeated rst-line immunotherapy still needed second-line immunotherapy due to unsatisfactory improvement, but this subset of patients showed no difference in complete recovery rate compared to patients from other treatment groups, suggesting repetitive rst-line immunotherapy can be considered when second-line immunotherapy is not applicable due to severe adverse effects or high costs, and delaying second-line immunotherapy in patients with repetitive rst-line immunotherapy did not affect outcome.
We found the relapse rate of oral prednisolone group was higher than that of other treatment groups, indicating using second-line or repetitive rst-line immunotherapy was bene cial to reduce relapses. More than half of patients who kept on oral prednisolone in our series used long-term regimen (> 3 months).
However, long-term use of corticosteroid can cause multiple adverse effects, such as cushingoid features (redistribution of body fat with truncal obesity, buffalo hump, and moon face), osteoporosis, infections, growth impairments and so on. We found no difference in complete recovery rate and relapse rate between patients using short-term (≤ 3 months) and long-term (> 3 months) regimens. Therefore, shortening the duration of prednisolone use is worth considering after fully evaluating patients' conditions.
However, there are limitations to our study. First, selection bias may exist because all hospitals involved in our study are major tertiary hospitals that usually accept more patients with critical conditions than hospitals in rural area. Second, evaluation of outcomes was conducted at different time points across patients. Since we are aware that recovery from this disease can be slow and take 18 months or longer.
Many patients can recover further as follow-up duration extending. Third, the outcome evaluated via mRS is dichotomous, focusing on the locomotor performance. However, multiple studies described pediatric patients could show some neuropsychological sequela, such as cognitive and social functioning de cits, even up until adolescence, causing learning issues (11)(12)(13). Thus, prospective longitudinal studies will be required to have better control of these confounding factors to pursue better interventions for this disease.

Conclusions
In conclusion, for patients with mRS ≥ 4 after rst-line immunotherapy, we recommend more aggressive treatments like second-line immunotherapy. When second-line immunotherapy is not applicable due to severe adverse effects or other reasons, repetitive rst-line immunotherapy can be considered as an option. Both second-line and repetitive rst-line immunotherapy are bene cial to reduce relapse rate. The treatment course of sequential oral prednisolone, as a routine maintenance treatment, can be shortened after fully evaluate patients' conditions.

Consent for publication
Not applicable.

Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding
This study is funded by National Natural Science Foundation of China (82071462).
Authors' contributions analyzed the data and revised the manuscript for intellectual content. Treatment strategies for pediatric patients with anti-NMDAR encephalitis