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Pitfalls in the detection of myositis specific antibodies by lineblot in clinically suspected idiopathic inflammatory myopathy

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12

  1. Department of Rheumatology, Ghent University Hospital, and Department of Rheumatology, AZ Sint-Jan Brugge - Oostende AV, Belgium. yves.piette@ugent.be
  2. Department of Laboratory Medicine, Ghent University Hospital, Belgium.
  3. Department of Laboratory Medicine, Ghent University Hospital, Belgium.
  4. Department of Paediatric Rheumatology, Ghent University Hospital, Belgium.
  5. Department of Neurology, Ghent University Hospital, Belgium.
  6. Department of Rheumatology, Ghent University Hospital, Belgium.
  7. Department of Rheumatology, Ghent University Hospital, Belgium.
  8. Department of Dermatology, Ghent University Hospital, Belgium.
  9. Department of Rheumatology, Ghent University Hospital, Belgium.
  10. Department of Internal Medicine, Ghent University and Praktijk 10A, Maldegem, Maldegem, Belgium.
  11. Department of Rheumatology, Ghent University Hospital, and Praktijk 10A, Maldegem, Belgium.
  12. Department of Laboratory Medicine, Ghent University Hospital, and Department of Diagnostic Science, Ghent University, Belgium.

CER12148 Submission on line
Full Papers

Rheumatology Article
Rheumatology Article

 

Abstract

OBJECTIVES:
Today, the contribution of myositis-specific autoantibodies (MSA) in the diagnostic workup of idiopathic inflammatory myopathies (IIM) is on the rise. The aim of this study was to document MSA frequency as detected by lineblot in a set of consecutive MSA requests and to correlate the results with clinical diagnosis, IIM subtype and indirect immunofluorescence (IIF) findings. Additionally, a comparison between two lineblots was performed.
METHODS:
A total of 118 consecutive samples of patients with suspicion of IIM were analysed on IIF and two lineblots. A total of 107 patients with autoimmune rheumatic diseases served as controls.
RESULTS:
MSA were detected in 55% of IIM patients (n=31) and 7.9% (n=12) of patients without clinical diagnosis of IIM or myositis overlap syndrome. All the IIM patients had a MSA-compatible clinical subtype. There was no to fair agreement between both lineblots for the individual antibodies, with most discrepancies observed for anti-TIF1γ (κ=-0.021), anti-SRP (κ=-0.006) and anti-SAE (κ=0.395). Differences between both assays were mostly observed in the non-IIM patients, also showing signi cantly lower blot signal intensities compared to IIM patients (p=0.0013). MSA in the non-IIM patients frequently showed an incompatible IIF pattern.
CONCLUSIONS:
Lineblot seems to be an interesting tool for MSA detection in a clinical context, allowing the identification of clinical subtypes. However, considerable caution must be exercised in interpreting the results in case of low positive MSA signal intensity, discordant lineblot results and/or an incompatible IIF pattern.

PMID: 31287411 [PubMed]

Received: 11/02/2019 - Accepted : 29/04/2019 - In Press: 04/07/2019