Myositis specific and associated autoantibodies (MSA-ab)

Date 24 November 2021

256th ENMC International Workshop:

Location: Hoofddorp, The Netherlands

Title: Myositis specific and associated autoantibodies (MSA-ab)

Date: 8-10 October 2021

Organisers: Prof. Y. Allenbach (France), Dr. J. Damoiseaux (The Netherlands), Prof. A. Mammen (United States)

Translations of this report by:
Prof. O. Benveniste, Prof. I. Lundberg, Mrs. I. de Groot, Mr. L. Mischke, Prof. J. Vencovský, Dr. G. Wang, Albert Selva O'Callaghan

Chinese translation

Swedish translation 

German translation 

Dutch translation

Czech translation 

French translation

Spanisch translation

Participants: Workshop attendees included a multidisciplinary group of 20 participants from 10 countries comprising clinicians from different disciplines, laboratory specialists, researchers and patient representatives. Due to COVID-19 restrictions about half of the participants attended the meeting on-line.

Background information: Idiopathic inflammatory myopathies (IIM) represent different subtypes: dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), anti-synthetase syndrome (ASyS), inclusion body myositis (IBM), overlap myositis (OM), and polymyositis (PM). These subtypes differ in clinical manifestations, prognosis, and therapeutic options. In the last decades multiple autoantibodies have been discovered that support the diagnosis and add information on subtype and prognosis. Detection of myositis-specific autoantibodies (MSA) was originally restricted to research laboratories, but nowadays several commercial assays have become available, enabling widespread introduction of the assays in clinical laboratories.

Workshop aims: To enable optimal interpretation of the test-results of the assays for MSA, the workshop had the following aims:

  • Define the clinical indications that ask for screening for MSA
  • Define the optimal testing strategy for patients suspected of IIM
  • Harmonize the way or reporting results to the clinician in order to enable optimal interpretation.

Workshop outcomes/deliverables:

Define the clinical indication that ask for screening for MSA. There was consensus that MSA add value in terms of diagnosis, subtyping and prognosis of IIM. MSA-testing should only be requested by clinicians that have relevant expertise (that is, not by general practitioners). Testing is warranted during the diagnostic work-up of patients suspected of having IIM. In addition, retesting is to be considered in case of inconsistencies, and only in exceptional cases during routine follow-up.

Define the optimal testing strategy for patients suspected of IIM. Detection for MSA should not start with screening for antinuclear antibodies (ANA), but with direct screening for the whole panel of MSA. No gold-standard methods were defined, but it was recognized that detection of some autoantibodies may be of insufficient quality in certain commercial assays.

Harmonize the way or reporting results to the clinician in order to enable optimal interpretation. Test results for MSA should be reported in a semi-quantitative manner, differentiating between low, medium, and high positive. The report should include all autoantibodies that have been tested for in combination with information on the assay used. Importantly, a positive finding for anti-MDA5 antibodies, possibly associated with rapidly progressive lung disease, demands urgent medical attention.

Outcome for the patients and their families: The patients will benefit from a better understanding of the clinical usefulness of MSA in terms of diagnosis, subtyping and prognosis by their treating clinician.

Next steps: A multi-center study will be designed in order to better determine the test-characteristics of the individual MSA in relation to the associated clinical manifestations. This will improve the interpretation of the test results.

A full report is published in Neuromuscular Disorders (Full report 256)