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Background and purpose During the COVID‐19 pandemic, myasthenia gravis (MG) patients have been identified as subjects at high risk of developing severe COVID‐19, and thus were offered vaccination with priority. The lack of direct data on the safety and tolerability of SARS‐CoV‐2 vaccines in MG have contributed to vaccine hesitancy. To address this issue, the safety and tolerability of SARS‐CoV‐2 vaccines were assessed in a large cohort of MG patients from two referral centers. Methods Patients with confirmed MG diagnosis, consecutively seen between October and December 2021 at two MG centers, were enrolled. Demographics, clinical characteristics, and information regarding SARS‐CoV‐2 infection/vaccination were extracted from medical reports and/or collected throughout telephonic or in‐person interviews. Results Ninety‐eight (94.2%) of 104 patients included were administered at least two vaccine doses 4 weeks before the interview or earlier, and among them, 63 of 98 (64.2%) have already received the “booster” dose. The most frequently used vaccines were BNT162b2‐Pfizer‐BioNTech and mRNA‐1273‐Moderna. Overall, only minor side effects were reported, most commonly local pain and fever. MG worsening after vaccination was observed in eight of 104 (7.7%) cases. The frequency of worsening among muscle‐specific tyrosine kinase MG cases (3/9, 33.3%) was significantly higher compared to other serological subgroups. Spontaneous symptom regression was observed in six of eight cases. Twelve of 104 (11.5%) patients had SARS‐CoV‐2 infection, and none of the SARS‐CoV‐2‐infected MG patients worsened after vaccination. Conclusions Our data support the safety and tolerability of mRNA COVID‐19 vaccines, which should be strongly recommended in MG patients, who could be at higher risk of complications if exposed to SARS‐CoV‐2 infection.

ObjectivePatients with myasthenia gravis without acetylcholine receptor (AChR) or muscle-specific kinase (MuSK) antibodies detected by radioimmunoprecipitation assays (RIAs) are classified as seronegative myasthenia gravis (SNMG). Live cell-based assays (l-CBAs) can detect additional antibodies to clustered AChR, MuSK and low-density lipoprotein receptor-related protein 4 (LRP4), but positivity rates are variable and both clinical relevance and utility of CBA platforms remain unclear.MethodsSera from 82 patients with SNMG were tested by l-CBAs. Human embryonic kidney cells were transfected to individually express clustered AChR, MuSK or LRP4; or transfected to jointly express both clustered adult AChR and MuSK. Sera from 30 and 20 patients positive by RIA for AChR or MuSK antibodies were used as comparators.Results53 of 82 (72%) patients with SNMG had generalised and 29 (28%) had ocular disease. The clustered AChR CBA detected antibodies in 16 of 82 patients (19.5%; including 4 patients with solely fetal AChR antibodies), while 7 of 82 (8.5%) patients had MuSK antibodies. A novel exploratory combined adult AChR-MuSK l-CBA efficiently detected all these antibodies in a subset of the SNMG cohort. No LRP4 antibodies were identified. Overall, patients with SNMG with clustered AChR antibodies, CBA-positive MuSK-MG or triple seronegative were younger, had less severe disease than patients with RIA-positive MG and had a better clinical outcome when immunotherapy was started soon after disease onset, although the time interval from onset to immunotherapy was not different when compared with patients with RIA-positive MG.ConclusionAround one-third of patients with SNMG had AChR or MuSK antibodies by l-CBAs, which were efficiently detected with a combined l-CBA. The results in this large and unselected cohort of patients with MG demonstrate the diagnostic usefulness of performing CBAs and the importance of making these tests more widely available.

Background and ObjectivesLive cell-based assay (CBA) can detect acetylcholine receptors (AChRs) or muscle-specific tyrosine kinase (MuSK) antibodies (Abs) in a proportion of patients with radioimmunoassay (RIA)-double seronegative myasthenia gravis (dSN-MG). A commercial fixed CBA for AChR and MuSK Abs has recently become available; however, comparative studies on fixed and live CBAs are lacking. In this study, we compared the performance of fixed and live CBAs in patients with RIA-dSN MG and assessed their sensitivity in RIA-positive MG samples and their specificity.MethodsAChR and MuSK Abs were tested in 292 serum samples from 2 Italian MG referral centers by live and fixed CBAs: 192 from patients with MG and 100 from controls. All samples had been previously assessed by RIA: 66 were AChR positive, 40 MuSK positive, and 86 dSN. All controls were negative. Two independent raters assessed the CBA results. Fixed and live CBAs were compared with the McNemar test; interrater and interlaboratory agreement were assessed with Cohen's kappa or interclass correlation coefficient (ICC), as appropriate.ResultsIn 86 RIA-dSN samples, fixed CBA detected Abs in 10 cases (11.6%, 95% CI 5.7–20.3), whereas live CBA detected Abs in 16 (18.6%, 95% CI 11.0–28.5) (p= 0.0143). Of these sera, those positive by fixed CBA were also positive by live CBA. In addition, live CBA could detect MuSK Abs in 4 and AChR Abs in 2 samples that were negative by fixed CBA, providing an 8% (95% CI 2.9–16.6) further increase in the Ab detection rate. These results were confirmed by flow cytometry. In the RIA-positive cohort, the sensitivity for AChR Abs was 98.5% (95% CI 91.9%–99.9%) for fixed CBA and 100% (95% CI 94.6–100) for live CBA (p= 0.1573). For both assays, the sensitivity for MuSK Abs was 100% (95% CI 91.2–100), and the specificity was 100% (95% CI 96.4–100). Interrater agreement was almost perfect for live and fixed CBAs (Cohen's kappa 0.972 and 0.978, respectively), alike interlaboratory agreement. Interrater agreement for the CBA score ranged from good to excellent (ICC: 0.832–0.973).DiscussionFixed CBA represents a valuable alternative to RIA for AChR and MuSK Ab detection in patients with MG and could be considered as a first-step diagnostic test. Live CBA can be useful in the serologic evaluation of RIA- and fixed CBA-negative samples.