The reliability of immunoassays to detect autoantibodies in patients with myositis is dependent on autoantibody specificity

OBJECTIVES: In order to address the reliability of commercial assays to identify myositis-specific and -associated autoantibodies, we aimed to compare the results of two commercial immunoassays with the results obtained by protein immunoprecipitation.METHODS: Autoantibody status was determined using radio-labelled protein immunoprecipitation for patients referred to our laboratory for myositis autoantibody characterization. For each autoantibody of interest, the sera from 25 different patients were analysed by line blot (Euroline Myositis Antigen Profile 4, EuroImmun, Lübeck, Germany) and dot blot (D-Tek BlueDiver, Diagnostic Technology, Belrose, NSW, Australia). Sera from 134 adult healthy controls were analysed.RESULTS: Overall commercial assays performed reasonably well, with high agreement (Cohen's κ &gt;0.8). Notable exceptions were the detection of rarer anti-synthetases with κ &lt; 0.2 and detection of anti-TIF1γ, where κ was 0.70 for the line blot and 0.31 for dot blot. Further analysis suggested that the proportion of patients with anti-TIF1γ may recognize a conformational epitope, limiting the ability of blotting-based assays that utilize denatured antigen to detect this clinically important autoantibody. A false-positive result occurred in 13.7% of samples analysed by line blot and 12.1% analysed by dot blot.CONCLUSION: The assays analysed do not perform well for all myositis-specific and -associated autoantibodies and overall false positives are relatively common. It is crucial that clinicians are aware of the limitations of the methods used by their local laboratory. Results must be interpreted within the clinical context and immunoprecipitation should still be considered in selected cases, such as apparently autoantibody-negative patients where anti-synthetase syndrome is suspected.</p

Serological subsets of juvenile idiopathic inflammatory myopathies - an update

In this review we explore the different characteristics of the serological phenotypes identified in juvenile-onset myositis and consider how the serological sub-classification of patients with juvenile myositis can be advantageous both in terms of reaching what can be a difficult diagnosis and informing on prognosis. Recent studies have described the autoantibody associated disease phenotypes and outcome for those with juvenile-onset disease and include analyses of large juvenile-onset myositis cohorts. Here we describe the autoantibody associated disease features for patients within juvenile-onset myositis in detail and discuss the expanding opportunities and strategies for myositis specific autoantibody testing in clinical practice.</p

A Commercial Anti-TIF1γ ELISA Is Superior to Line and Dot Blot and Should Be Considered as Part of Routine Myositis-Specific Antibody Testing

OBJECTIVES: Anti-TIF1γ is an important autoantibody in the diagnosis of cancer-associated dermatomyositis and the most common autoantibody in juvenile onset dermatomyositis. Its reliable detection is important to instigate further investigations into underlying malignancy in adults. We previously showed that commercial assays using line and dot blots do not reliably detect anti-TIF1γ. We aimed to test a new commercial ELISA and compare with previously obtained protein immunoprecipitation. METHODS: Radio-labelled immunoprecipitation had previously been used to determine the autoantibody status of patients with immune-mediated inflammatory myopathies and several healthy controls. ELISA was undertaken on healthy control and anti-TIF1γ sera and compared to previous immunoprecipitation data. RESULTS: A total of 110 serum samples were analysed: 42 myositis patients with anti- TIF1γ and 68 autoantibody negative healthy control sera. Anti-TIF1γ was detected by ELISA in 41 out of 42 of the anti-TIF1γ-positive samples by immunoprecipitation, and in none of the healthy controls, giving a sensitivity of 97.6% and specificity of 100%. The false negative rate was 2%. CONCLUSION: ELISA is an affordable and time-efficient method which is accurate in detecting anti-TIF1γ

Anti-HMGCR Autoantibodies in Juvenile Idiopathic Inflammatory Myopathies Identify a Rare but Clinically Important Subset of Patients

Objective.We aimed to establish the prevalence and clinical associations of anti-HMG-CoA-reductase (anti-HMGCR) in a large UK cohort with juvenile myositis.Methods.There were 381 patients investigated for anti-HMGCR using ELISA.Results.Anti-HMGCR autoantibodies were detected in 4 patients (1%). These children had no or minimal rash and significant muscle disease. Muscle biopsies were considered distinctive, with widespread variation in fiber size, necrotic fibers, and chronic inflammatory cell infiltrates; all had prolonged elevation of creatine kinase and all ultimately received biologic therapies.Conclusion.Anti-HMGCR in UK children with myositis are associated with severe disease that is poorly responsive to standard treatment.</jats:sec