Enhanced antibody detection via live cell-based assay among RIA negative myasthenia gravis patients: toward improved diagnosis and clinical correlates.

BACKGROUND

Radioimmunoprecipitation assay (RIA) is the gold standard for antibody detection in myasthenia gravis (MG), while fixed cell-based assays (CBAs) are widely used as second-line or first-line tests. Live CBA represents an alternative approach and its combined use with fixed CBA may improve diagnostic sensitivity. Our aim was to evaluate the diagnostic yield of fixed and live CBA for AChR and MuSK antibodies in a large cohort of RIA seronegative MG patients and to investigate clinical associations and outcomes.

METHODS

Sera from 124 AChR- and MuSK-RIA seronegative MG patients and 72 control samples were tested using fixed CBA for fetal and adult AChR isoforms and MuSK. All sera were also analyzed with an in-house live CBA, with cells expressing clustered AChR or MuSK.

RESULTS

Fixed CBA identified AChR antibodies in 3/124 (2.4%) patients, all with mild early-onset MG; none were MuSK positive. Live CBA detected AChR antibodies in 11 (8.9%) and MuSK antibodies in 13 (10.5%) patients. Live CBA seronegative patients were predominantly female (77/100, 77%) compared with AChR-live (4/11, 36.4%) and MuSK-live (7/13, 53.8%) groups (p = 0.0068), and more frequently had generalized MG (87% vs 53.8% in MuSK-live; p = 0.0146). Unchanged or worsened MGFA-PIS occurred in 4/13 (30.8%) of MuSK-live patients and 18/82 (21.9%) of live CBA seronegative patients, whereas all AChR-live CBA patients achieved minimal manifestations or better.

CONCLUSION

Live CBA identifies AChR or MuSK antibodies in approximately 20% of RIA seronegative MG patients and provides clinically meaningful subgroup stratification. Fixed CBA performed only slightly better than RIA.