Cell-Based Assay Outperforms Others for Antibody Detection in Myasthenia Gravis

Cell-based assay (CBA) was more diagnostically accurate compared with radioimmunoprecipitation assays (RIPA) and an enzyme-linked immunosorbent assay (ELISA) when utilized to detect acetylcholine receptor (AChR) and muscle-specific kinase (MuSK) autoantibodies among patients with suspected cases of myasthenia gravis (MG), according to a new study published in The Lancet Regional Health: Western Pacific.¹

“Thus, the current guidelines for the diagnosis of MG generally lack evidence-based recommendations on methodology for detecting AChR and MuSK autoantibodies,” the study authors wrote. “This may impact the accuracy in clinical decision making across centres and poses a challenge for neurologists managing MG patients and conducting clinical trials.”

Among the 2272-patient cohort, there were 2043 patients with MG (1110 had generalized MG [GMG] and 933 had ocular MG [OMG]) and 229 who did not have the chronic autoimmune disorder—but among whom 73.4% received an ultimate diagnosis of peripheral neuropathy, Guillain–Barré syndrome, Lambert–Eaton myasthenic syndrome, amyotrophic lateral sclerosis, external ophthalmoplegia, congenital myasthenia syndrome, cavernous sinus syndrome—which is characterized by weakened skeletal muscles resulting from antibody-induced broken communication paths between nerves and muscle caused.²

The study authors searched PubMed and Web of Science for articles published between January 1, 1970, and December 30, 2020, that detailed previous evidence on methodologies in detecting AChR and/or MuSK antibodies by using the terms cell-based assay (CBA), radioimmunoprecipitation assay (RIPA), enzyme-linked immunosorbent assay (ELISA), acetylcholine receptor (AChR), muscle-specific kinase (MuSK), and myasthenia gravis (MG).

Among the patients with suspected MG, the highest sensitivity rate for AChR antibodies was seen following use of CBA (72.3%; 95% CI, 70.3%-74.3%), followed by RIPA (64.1%; 95% CI, 62.0%-66.2%) and ELISA (62.7%; 95% CI, 60.5%-64.8%). The corresponding specificity rates were significantly higher at 97.8% (95% CI, 95.0%-99.3%), 97.8% (95% CI, 95.0%-99.3%), and 94.8% (95% CI, 91.9%-97.7%).

For MuSK antibodies, CBA again had the highest sensitivity rating vs RIPA and ELISA:

• CBA: 2.9% (95% CI, 2.2%3.7%)
• RIPA: 2.4% (95% CI, 1.8%-3.2%)
• ELISA: 2.6% (95% CI, 2.0%-3.4%)

Specificity ratings for MuSK antibodies were 100% (95% CI, 98.4%-100.0%), 100% (95% CI, 98.4%-100.0%), and 99.1% (95% CI, 96.%-99.9%) for CBA, RIPA, and ELISA, respectively.

Statistically significant differences were seen between the area under the curve (AUC)—which measures quantitative diagnostic test accuracy³—for CBA-tested AChR antibodies (0.858) and RIPA- (0.843; P = .03) and ELISA (0.809; P < .0001).

Patients were recruited for this analysis between January 1, 2021, and September 30, 2022, from 9 centers in China that care for patients who have MG. Their illness was diagnosed via differential diagnosis through tests that included pharmacological neostigmine test, thymic CT, and MRI and confirmed by 2 consulting neurologists. The mean (SD) patient age of the MG cohort was 47.1 (20.6) years, and of the control group, 52.6 (15.9) years. Most patients in each group were female patients, at 62.1% and 53.3%, respectively.

Digging deeper by MG subtype, for OMG, the AUC of CBA-detected AChR antibodies was 0.802 (95% CI, 0.782-0.82), which was higher than both RIPA (0.785; 95% CI, 0.763-0.81]; P = .107) and ELISA (0.736; 95% CI, 0.71-0.762]; P < .0001). For GMG, similar results were seen, with CBA again having the highest AUC (0.904; 95% CI, 0.89-0.91), followed by RIPA (0.892; 95% CI, 0.877-0.91; P = .0255) and ELISA (0.869; 95% CI, 0.85-0.89; P < .0001). When looking at MuSK antibody AUC, statistical differences were not seen between the 3 methodologies, which came in at 0.514 (95% CI, 0.49-0.53), 0.513 (95% CI, 0.49-0.53; P = .1572), and 0.505 (95% CI, 0.48-0.52; P = .062, for CBA, RIPA, and ELISA, respectively.

“The CBA assay increased the total absolute yield of AChR or MuSK antibodies in MG patients and maintained a high diagnostic specificity compared to that of the RIPA and ELISA,” the study authors noted. “This study provides high-level evidence supporting CBA as a first-line assay in the diagnosis and management of MG as well as evaluating patients with suspected MG for whom AChR or MuSK antibodies are undetectable by RIPA or ELISA assays.”

Reference

1. Li Z, Zhang C, Chang T, et al; SCREAM study investigators. A multicentre, prospective, double-blind study comparing the accuracy of autoantibody diagnostic assays in myasthenia gravis: the SCREAM study. Lancet Reg Health West Pac. 2023;38:100846. doi:10.1016/j.lanwpc.2023.100846

2. Myasthenia gravis. Johns Hopkins Medicine. Accessed August 16, 2023. https://www.hopkinsmedicine.org/health/conditions-and-diseases/myasthenia-gravis

3. Area under the curve. Analyse-it. April 18, 2023. Accessed August 16, 2023. https://analyse-it.com/docs/user-guide/diagnostic-performance/auc