Concordance between radioimmunoassay and fixed cell‐based assay in subjects without myasthenia gravis: optimizing the diagnostic approach

• Published in: European journal of neurology Vol. 31; no. 12; pp. e16435 - n/a
• Main Authors: Falso, Silvia, Marini, Sofia, Carrozza, Cinzia, Sabatelli, Eleonora, Mascagna, Giovanni, Marini, Martina, Morroni, Jacopo, Evoli, Amelia, Iorio, Raffaele
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.12.2024; John Wiley and Sons Inc
• Subjects: Adult; Aged; autoantibodies; Autoantibodies - blood; autoimmune; Diagnosis; diagnostic tests; Electrophysiology; Epitopes; Female; Humans; Male; Medical records; Middle Aged; Muscle and MNJ Disorders; Myasthenia gravis; Myasthenia Gravis - blood; Myasthenia Gravis - diagnosis; Myasthenia Gravis - immunology; nervous system; neuromuscular junction; Neuromuscular junctions; Radioimmunoassay; Radioimmunoassay - methods; Radioimmunoassay - standards; Receptors, Cholinergic - immunology; Retrospective Studies; Sensitivity and Specificity; Short Communication; Thymoma; diagnostic tests; nervous system; autoimmune; neuromuscular junction; autoantibodies
• ISSN: 1351-5101; 1468-1331; 1468-1331
• DOI: 10.1111/ene.16435

Background and Purpose Acetylcholine receptor antibody (AChR‐Ab) detection is crucial in myasthenia gravis (MG) diagnosis and, currently, the radioimmunoassay (RIA) is the gold standard. However, RIA may detect AChR‐Ab against nonpathogenic intracellular epitopes. In this study, we performed fixed cell‐based assay (F‐CBA) in RIA‐AChR‐Ab positive subjects without MG symptoms, to assess whether F‐CBA could show a higher specificity compared to RIA in detecting pathogenic Abs. Methods We reviewed medical records of patients referred to our MG outpatient clinic because of RIA‐AChR‐Ab detection. MG diagnosis was based on clinical examination, electrophysiology and Ab detection. AChR‐Abs were tested by RIA in the whole cohort. Serum samples from RIA‐positive asymptomatic subjects were retested by F‐CBA. Results Of 605 subjects who tested RIA‐AChR‐Ab positive, MG diagnosis was confirmed in 599. Six subjects were RIA‐AChR‐Ab positive although they had never had MG symptoms; in four of these subjects AChR‐Abs were not detected by F‐CBA, whereas the remaining two (both non‐MG thymoma cases) were positive also by F‐CBA. Conclusions RIA false positivity for AChR‐Ab is very rare. Previous literature has demonstrated that F‐CBA has higher sensitivity than RIA for MG, especially in ocular cases. Our preliminary results show that, in rare instances, F‐CBA may be more specific than RIA for MG diagnosis.