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

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.

Comparison of Fixed and Live Cell-Based Assay for the Detection of AChR and MuSK Antibodies in Myasthenia Gravis.

BACKGROUND AND OBJECTIVES: Live 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. METHODS: AChR 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. RESULTS: In 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). DISCUSSION: Fixed 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.

Bile acids and total bilirubin detection in saliva of patients submitted to gastric surgery and in particular to subtotal Billroth II resection.

OBJECTIVE: The aim of our study was to detect bile acids and total bilirubin in saliva of gastrectomized patients, to confirm objectively presence of biliary laryngopharyngeal reflux and its relationship with laryngeal mucosa damage. SUMMARY BACKGROUND DATA: Recently, it has been hypothesized that biliary-reflux may reach the upper aerodigestive tract and enhance development of laryngeal malignancies; nevertheless, the presence of duodenogastric contents in this region has never been revealed. METHODS: We carried out a prospective observational case-control study on 52 patients (cases) previously submitted to gastric surgery, mainly to subtotal Billroth II resection, and on 51 healthy volunteers (controls). Patients were submitted to clinical interview, esophagogastroduodenal endoscopy, endoscopic laryngeal evaluation, and saliva collection. In all saliva samples, bile acids, total bilirubin, and pepsinogen II were assayed. RESULTS: In cases, group bile acids levels were recorded in 17 of 52 (32.6%) patients, while in 35 of 52 (67.4%) they were undetectable. All controls were negative to bile acids. In positive cases to bile acids, we found a significant (P < 0.05) correlation between bile acids, total bilirubin, and pepsinogen II values and a significant (P < 0.05) higher prevalence of symptoms and findings of laryngeal damage and of previous laryngeal neoplastic lesions. CONCLUSIONS: We found detectable levels of bile acids and total bilirubin in saliva of patients submitted to previous gastric surgery, prospecting an intriguing diagnostic role of this dosage in the study of biliary laryngopharyngeal reflux. We finally revealed a high incidence of laryngeal disorders in patients with positive bile acids in saliva.