Clinical contribution of myositis-related antibodies detected by immunoblot to idiopathic inflammatory myositis: A one-year retrospective study

Clinical relevance of positively determined myositis antibodies in rheumatology: a retrospective monocentric analysis

BACKGROUND

The increased availability of myositis autoantibodies represents new possibilities and challenges in clinical practice (Lundberg IE, Tjärnlund A, Bottai M, Werth VP, Pilkington C, de Visser M, et al. 2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups. Ann Rheum Dis. 2017;76:1955-64. https://doi.org/10.1136/annrheumdis-2017-211468 .). The aim of this study was to perform a retrospective data analysis of patient cases with positive myositis autoantibodies to analyse their significance in routine rheumatology practice.

METHODS

A monocentric analysis of all the orders used to determine myositis autoantibodies from July 2019 to May 2022 in the Department of Rheumatology, Krankenhaus Porz am Rhein, Cologne, Germany, was carried out.

RESULTS

In the defined time interval, a total of 71,597 laboratory values for the antibodies mentioned above were obtained. A total of 238 different positive autoantibodies ​​were detected in 209 patients. Idiopathic inflammatory myopathy was diagnosed in 37 patients (18%), and inflammatory rheumatic diseases other than idiopathic inflammatory myopathy were diagnosed in 90 patients (43%). No inflammatory rheumatic disease was diagnosed in 82 patients (39%). General clusters of clinical manifestations were observed.

CONCLUSIONS

In our cohort, we were able to show that a relevant proportion of patients with positive myositis antibodies did not have idiopathic inflammatory myopathies or inflammatory rheumatic diseases. This finding indicates the importance of myositis autoantibodies in this group of patients. However, further studies on the course of symptoms and examination results in patients without inflammatory rheumatic diseases and with positive myositis antibodies are necessary.

Positive predictive value of myositis antibody line blot testing in patients with suspected idiopathic inflammatory myopathy

INTRODUCTION/AIMS

Line blot (LB) is in widespread use for myositis antibody detection. Yet, studies of its positive predictive value (PPV) in patients with suspected idiopathic inflammatory myopathy (IIM), which would be of particular relevance to neuromuscular clinicians, are lacking. We aimed to determine the PPV of myositis antibody LB testing in patients with suspected IIM, and examine whether PPV was significantly impacted by intensity of antibody positivity.

METHODS

This was a retrospective study of patients who underwent myositis antibody LB testing for suspected IIM between March 2019 and August 2022.

RESULTS

Of 70 patients who underwent testing for suspected IIM and had positive myositis antibody LB results, 43 (61%) were female and the median age was 61 years (range: 10-83 years). Forty-four were classified as true-positives, yielding a PPV of 63%. The PPV of patients with weak-positive myositis antibody results (14/30, 47%) was significantly lower than the PPV of patients with moderate-positive or strong-positive myositis antibody results (30/40, 75%) (p = .02).

DISCUSSION

Our study found that myositis antibody LB testing in patients with suspected IIM had a modest PPV, underscoring the need for antibody interpretation in the context of all available clinical and ancillary test data to avoid misdiagnosis. The significantly lower PPV in patients with weak-positive results emphasizes the particular importance of clinical correlation in such patients. Further study into the diagnostic performance of various LBs for myositis antibody detection is needed to inform their interpretation in clinical practice.

Association of extended myositis panel results, clinical features, and diagnoses: a single-center retrospective observational study

Myositis-specific antibodies (MSA) and myositis-associated antibodies (MAA) are a feature of the idiopathic inflammatory myopathies (IIM), but are also seen in other rheumatic diseases, and in individuals with no clinical symptoms. The aim of this study was to assess the clinical utility of MSA and MAA and in particular the clinical relevance of weakly positive results. We included all patients at our institution who had at least one positive result on the Immunoblot EUROLINE myositis panel over a 6-year period (2015-2020). Associations with clinical features and final diagnosis were evaluated. Eighty-seven of 225 (39%) myositis panel tests met the inclusion criteria. There were 52 strong positives and 35 weak positives for one or more MSA/MAAs. Among the strong positive group, 15% (8/52) were diagnosed with IIM, 34.6% (18/52) with interstitial lung disease, 7.7% (4/52) with anti-synthetase syndrome, 25% (13/52) with connective tissue disease, and others accounted for 25% (13/52). In weak-positive cases, only 14% (5/35) had connective tissue disease and none had IIM. 60% (21/35) of weak-positive cases were not associated with a specific rheumatic disease. A significant number of positive myositis panel results, particularly weak positives, are not associated with IIM or CTD.

Diagnosis of myositis-associated interstitial lung disease: Utility of the myositis autoantibody line immunoassay

OBJECTIVES

The detection of myositis autoantibodies (MA) in patients with interstitial lung disease (ILD) has major implications for diagnosis and management, especially amyopathic and forme frustes of idiopathic inflammatory myositis-associated ILD (IIM-ILD). Use of the MA line immunoblot assay (MA-LIA) in non-rheumatological cohorts remains unvalidated. We assessed the diagnostic performance of the MA-LIA and explored combined models with clinical variables to improve identification of patients with IIM-ILD.

METHODS

Consecutive patients referred to a specialist ILD clinic, with ILD-diagnosis confirmed at multidisciplinary meeting, and MA-LIA performed within six months of baseline were included. Pre-specified MA-LIA thresholds were evaluated for IIM-ILD diagnosis.

RESULTS

A total 247 ILD patients were included (IIM-ILD n = 12, non-IIM connective tissue disease-associated ILD [CTD-ILD] n = 52, idiopathic interstitial pneumonia [IIP] n = 115, other-ILD n = 68). Mean age was 64.8 years, with 45.3% female, mean FVC 75.5% and DLCO 59.2% predicted. MA were present in 13.8% overall and 83.3% of IIM-ILD patients. The most common MA in IIM-ILD and non-IIM ILD patients were anti-Jo-1 (prevalence 40%) and anti-PMScl (29.2%) autoantibodies respectively. The pre-specified low-positive threshold (>10 signal intensity) had the highest discriminative capacity for IIM-ILD (AUC 0.86). Combining MA-LIA with age, gender, clinical CTD-manifestations and an overlap non-specific interstitial pneumonia/organising pneumonia pattern on HRCT improved discrimination for IIM-ILD (AUC 0.96).

CONCLUSION

The MA-LIA is useful to support a diagnosis of IIM-ILD as a complement to multi-disciplinary ILD assessment. Clinical interpretation is optimised by consideration of the strength of the MA-LIA result together with clinical and radiological features of IIM-ILD.

Performance of myositis-specific antibodies detected on myositis line immunoassay to diagnose and sub-classify patients with suspected idiopathic inflammatory myopathy, a retrospective records-based review

AIM

To evaluate myositis line immunoassay (LIA) for diagnosis and sub-classification of suspected idiopathic inflammatory myopathy (IIM). To investigate if test performance is improved by increasing signal strength cut-off for myositis-specific antibody (MSA) or combining MSA with indirect immunofluorescence (IIF).

METHODS

A retrospective, consecutive case series of patients investigated for MSAs from June 2013 to June 2020 for suspected IIM. Specificity, sensitivity, positive predictive value, and negative predictive value were calculated with 95% confidence intervals for diagnosis of IIM. Association of IIM diagnosis with increased signal strength and presence of an expected IIF pattern on Hep-2 cells was assessed by Fisher's exact test in MSA-positive patients.

RESULTS

A total of 195 patients were evaluated. IIM was diagnosed in 32/195 (16.4%) patients. MSAs were detected in 41/195 (21%) patients, 18/41 (43.9%) patients with an MSA had a diagnosis of IIM. The probability of an IIM diagnosis was increased in MSA-positive patients with high compared with low signal strength (83.3% vs 43.5%; P = 0.01) and an expected compared with unexpected IIF pattern (61.5% vs 23.8%; P = 0.04). Specificity for IIM was not significantly improved by increasing signal strength cut-off (85.9% vs 93.8%). Positive predictive value of myositis LIA was only modest and not significantly improved by either increasing signal strength cut-off or requiring an expected IIF pattern for determination of MSA positivity (43.9% vs 60% vs 61.5%). Sub-classification of IIM correlated closely for respective MSAs (88.9%).

CONCLUSION

Increased MSA signal strength on myositis LIA and the presence of an expected IIF pattern were associated with IIM diagnosis. Test performance was non-significantly improved by these methods. Prevalence of IIM in this patient cohort was low; it is not excluded that LIA performance could be improved by these methods in a higher prevalence cohort.

Lack of standardisation in interpretation and reporting of autoantibody assays: a survey analysis of Australasian laboratories with focus on line immunoassays

Autoantibody assays are reported in a variety of formats. Results only slightly above established cut-offs provide lower likelihood ratios; therefore, their clinical significance may be more uncertain, which is not readily communicated with dichotomous qualitative reporting. Line immunoassays (LIA) are a common method for detecting antibodies to extractable nuclear antigens (ENA) and myositis-associated antibodies. However, recommended positive cut-offs are contentious. We distributed a survey via e-mail to participants in the Royal College of Pathologists of Australasia Quality Assurance Program (RCPAQAP) Immunology modules and to a dedicated immunology mailing list in Australasia. Questions explored general viewpoints surrounding autoantibody reporting, as well as current laboratory practices, with particular focus on interpretation and reporting of the most commonly used ENA LIA manufactured by Euroimmun. There were 31 responders, representative of at least 17 unique laboratories across Australia (8 public, 5 private) and New Zealand (4 laboratories). Responses suggest that autoantibody reporting is not standardised; there was variation in general viewpoints and reporting practices, particularly regarding the interpretation of and positive cut-offs used for the Euroimmun ENA LIA, which were contrary to the manufacturer's guidelines in a majority of the responses. Interpretative qualitative reporting based on results from other investigations and the clinical history was a common theme. There is large variation in the reporting of autoantibody assays within Australasia, especially by LIA. A majority of respondents report the most commonly used ENA LIA contrary to manufacturer's guidelines; alternative positive cut-offs are commonly utilised. LIA reports should indicate the level of positivity to enhance their relevance in the clinical decision-making process.

Viral antigen nanoparticles for discriminated and quantitative detection of different subtypes of anti-virus immunoglobulins

The aim of this study is to develop a novel method for the accurate diagnosis of the infection status of viral diseases, which requires discriminated and quantitative detection of different anti-virus immunoglubulin subtypes. Considering hepatitis A as a representative model disease, viral antigen nanoparticles (vAgNPs) were designed and synthesized by genetically presenting hepatitis A virus (HAV) antigens on the surface of human heavy chain ferritin (hFTH) nanoparticles to detect anti-HAV antibodies with discriminating immunoglobulin subtypes M and G (IgM and IgG, respectively). The vAgNPs also display multi-copies of hexa-histidine peptide (H6) on their surface to chemisorb gold ions (Au3+), which is vital for the autonomous generation of quantitatively meaningful detection signals. The quantitative level of anti-HAV IgM or IgG in 30 patient sera was successfully analyzed using the vAgNPs of HAV, which was performed through label-free one-step-immunoassay based on the self-enhancement of optical signals from gold nanoparticles clustered on the viral antigen nanoparticles. The diagnostic performance was compared with that of enzyme-linked immunosorbent assay (ELISA), which did not enable accurate quantitative assay due to the poor linearity between the antibody concentration and detection signal. Furthermore, these vAgNP-based immunoassays did not produce any false negative/positive signals, indicating 100% sensitivity and 100% specificity.

Frequencies and clinical associations of myositis-related antibodies in The Netherlands: A one-year survey of all Dutch patients

Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of connective tissue diseases, collectively known as myositis. Diagnosis of IIM is challenging while timely recognition of an IIM is of utter importance considering treatment options and otherwise irreversible (severe) long-term clinical complications. With the EULAR/ACR classification criteria (2017) considerable advancement has been made in the diagnostic workup of IIM. While these criteria take into account clinical parameters as well as presence of one autoantibody, anti-Jo-1, several autoantibodies are associated with IIM and are currently evaluated to be incorporated into classification criteria. As individual antibodies occur at low frequency, the development of line blots allowing multiplex antibody analysis has improved laboratory diagnostics for IIM. The Euroline myositis line-blot assay (Euroimmun) allows screening and semi-quantitative measurement for 15 autoantibodies, i.e. myositis specific antibodies (MSA) to SRP, EJ, OJ, Mi-2α, Mi-2β, TIF1-γ, MDA5, NXP2, SAE1, PL-12, PL-7, Jo-1 and myositis associated antibodies (MAA) to Ku, PM/Scl-75 and PM/Scl-100. To evaluate the clinical significance of detection and levels of these autoantibodies in the Netherlands, a retrospective analysis of all Dutch requests for extended myositis screening within a 1 year period was performed. A total of 187 IIM patients and 632 non-IIM patients were included. We conclude that frequencies of MSA and MAA observed in IIM patients in a routine diagnostic setting are comparable to cohort-based studies. Weak positive antibody levels show less diagnostic accuracy compared to positive antibody levels, except for anti-NXP2. Known associations between antibodies and skin involvement (anti-MDA5, anti-TIF1-γ), lung involvement (anti-Jo-1), and malignancy (anti-TIF1-γ) were confirmed in our IIM study population. The availability of multiplex antibody analyses will facilitate inclusion of additional autoantibodies in clinical myositis guidelines and help to accelerate diagnosing IMM with rare but specific antibodies.