Welcome to the Autoimmunity 2021 Congress Calendar

Background and Aims

Antinuclear antibodies (ANA) are essential in the diagnosis of systemic autoimmune rheumatic diseases (SARDs) and they could appear years before the clinical onset of the disease. Different assays for ANA screening are available, such as indirect immunofluorescence (IIF) on HEp-2 cells and Multiplex fluorescent immunoassay (MFI). This study aimed to clarify the importance of ANA detected only by IIF in the future development of SARDs and to recommend a laboratory algorithm that integrates the available diagnostic approaches to optimise the diagnosis of ANA IIF+MFI- subjects.

Methods

A total of 9,291 subjects with clinical suspicion of SARDs were evaluated for ANA by IIF and MFI. Only 198 subjects (2.1%) were ANA IIF+MFI- and were followed-up for 2 years. ANA were evaluated using IIF on HEp-2 cells and MFI on the BioPlex 2200.

Results

The ANA IIF+MFI- cohort consisted of 106 subjects with high clinical suspicion of SARDs, 26 subject with other autoimmune diseases (not-SARDs) and 66 subjects with minor symptoms or ANA requested in check-ups. Only 94 subjects underwent re-evaluation and were followed-up for 2 years. Most re-evaluated subjects (51 patients, 54%) became ANA negative by both assays (mainly rheumatoid arthritis, polymyalgia and inflammatory bowel disease patients) and 35 subjects remained ANA IIF+MFI- (37%, principally systemic sclerosis and systemic lupus erythematosus patients). A new algorithm for ANA evaluation was suggested.

Conclusions

According to the proposed algorithm, ANA IIF+MFI- subjects should be screened by an alternative solid-phase assay such as line-immunoassay or ELISA, where appropriate antigens for the diagnosis of SARDs are represented.

Background and Aims

Onconeural antibodies are well-known markers of paraneoplastic neurological syndromes (PNS). Antibody screening plays an important role in prompt tumour diagnosis because in up to 75% of patients the neurological symptoms precede the tumour diagnosis. Antibody detection based on brain tissue followed by antigen specific techniques, such as immunoblot, have demonstrated high sensibility and specificity for PNS. For practical reasons many clinical diagnostic laboratories use only immunoblot for onconeural antibody testing.

To assess the PNS-specificity of immunoblot for onconeural antibody testing.

Methods

We reviewed all the patients tested for onconeural antibodies from October 1, 2016 until August 31, 2019 by an in-house immunohistochemistry on paraformaldehyde perfused rat cerebellum and by a commercial line blot assay (PNS12 Euroline Blot, Euroimmun). Reasons for additional testing by blot were confirmation of a suspicious positive result by immunohistochemistry or specific request to test the sample by line blot.

Results

96 patients’ sera showed positive bands for onconeural antibodies using immunoblot. Immunoblot bands matched with the brain immunohystochemical findings in 45 patients (46.9%) whereas the other 51 (53.1%) showed discordant results. Clinical information was available in 45 and 46 patients respectively. 40 (88.9%) of the 45 patients with concordant immunoblot and immunohistochemistry results had PNS, whereas only 4 (8.7%) of the 46 patients with discordant results had PNS. Discordant results were more common with Yo (70%) and Zic4 (74%) antibodies.

Conclusions

Onconeural antibody testing by immunoblot is highly sensitive but shows low specificity for the diagnosis of PNS. This low specificity is more prominent for Yo and ZIC4 antibodies.

Background and Aims

Anti-cyclic citrullinated peptide (CCP) antibodies are the most specific markers for rheumatoid arthritis (RA). Different generations of assays (CCP1-CCP3) have been developed showing variability regarding their performance. The comparability of different assays is an important issue to address especially in the early stages of disease.

Methods

This study aimed to investigate the diagnostic performance of IgG and IgA anti-CCP2 detected by EliA^TM (Thermo Fisher Scientific) compared to the combined IgG/IgA Quanta Lite^R anti-CCP3.1 assay (Inova Diagnostics) in sera of 184 early RA patients, 98 healthy subjects and 360 disease controls.

Results

Anti-CCP2 IgG and IgA assays showed high specificity versus healthy (98.9%; 98%) and disease controls (98.8%; 99.4%). Sensitivity was 52.2% (IgG) and 30.4% (IgA), respectively, resulting in high positive likelihood ratios of 47.5 (IgG) and 50.7 (IgA). IgA antibodies had no added diagnostic value since all patients were also IgG positive. Anti-CCP3.1 was slightly more sensitive than the anti-CCP2 IgG (55.4%) but specificity was markedly lower and amounted to 95.9% versus healthy and 90.8% versus disease controls resulting in a LR+ of only 6.0. Out of 360 disease controls 33 (9.2%) were found to be positive for CCP3.1 but among these only four (1.1%) were positive for anti-CCP2 IgG. When applying 60 AU/ml (high positive) as cut-off value for CCP3.1, sensitivity (52.7%) became comparable to the anti-CCP2 assay and both specificity (97.5%) and LR+ (21.08) increased substantially.

Conclusions

Thus, specificity of anti-CCP assays should be taken into account when interpreting results in order to reduce the risk of a false positive diagnosis.

Background and Aims

Inclusion Body Myositis (IBM) is the most frequent myositis among the population over 50 years of age. Clinical and histological criteria enable the diagnosis of this disease. However, in some cases, a biological marker could be of interest like autoantibodies to cytosolic 5'-nucleotidase 1A (cN1A) or 43/44 kDa muscle protein (Mup 44).

The objective of this study was to evaluate retrospectively the clinical diagnostic value of these new antibodies.

Methods

Sera obtained from 44 patients with a definite (n=24) or suspected (n=20) IBM considering classical diagnostic criteria which were followed in clinical departments of different French centers during the last year were analyzed for anti-cN1A antibodies using a commercial ELISA technique (Euroimmun). Twenty five sera from patients with idiopathic inflammatory myopathy or myositis (9 polymyositis, dermatomyositis or anti-synthetase syndrome, 16 other myositis) were analyzed as controls.

Results

Seventeen sera out of 24 definite IBM and 4 out of 20 suspected IBM were found positive for anti-cN1A antibodies using the manufacturer’s cut-off value of 1 AU indicating a prevalence of 71% and 20% respectively whereas only 3 out of the 25 controls (12%) were positive.

Conclusions

In conclusion, despite a known prevalence of anti-cN1A antibodies in 20 to 26% of connective tissue diseases (mostly Sjögren’s Syndrome and lupus), their specificity in our study among myopathies is 88% when compared to similar idiopathic inflammatory myopathy or myositis diseases. Anti-cN1A antibodies could be thus useful for a better diagnosis of IBM and could be proposed as a biomarker of IBM.