The 272nd ENMC international workshop, held in June 2023, focused on revising and updating the diagnostic criteria for inclusion body myositis (IBM). Clinical trial readiness for IBM was also discussed. Significant advancements have been made in the understanding and diagnosis of IBM since the publication of the previous 2013 ENMC criteria.
IBM is a rare, age-associated myopathy, which typically affects people over the age of 45. It presents with at least 12 months of progressive muscle weakness, especially in the deep finger flexors and knee extensors. Dysphagia is an important symptom of IBM with aspiration pneumonia followed by respiratory failure being the leading cause of death in patients with IBM. The pathogenesis of IBM involves both inflammatory and myodegenerative mechanisms, with evidence suggesting that inflammation drives muscle degeneration. Key features include the clonal expansion of cytotoxic T cells and B cells attacking muscle fibers. The B-cell involvement may be related with the presense of cytosolic 5'-nucleotidase-1A auto-antibodies (anti-cN1a) in a subset of IBM patients.
The revised 2024 ENMC diagnostic criteria for IBM are more inclusive and simpler. It comprises a two-step approach to improve diagnostic accuracy:
(1) determination of the clinical presentation type;
(2) confirmatory investigations, including muscle imaging techniques (magnetic resonance and ultrasound), and serological testing for anti-cN1a.
Key changes in diagnostic criteria regard the clinical presentation. The criteria now include patients with typical and atypical presentations. Typical IBM presents with progressive weakness in deep finger flexors or knee extensors, often accompanied by dysphagia. Atypical presentation is also recognized, including axial weakness, isolated dysphagia, foot drop, facial diplegia, or proximal limb weakness.
Crucial alterations in additional investigations have also been made. Mandatory myopathological evidence of inflammation includes endomysial lymphocytes surrounding non-necrotic muscle fibers. Supportive features are rimmed vacuoles, cytoplasmic protein aggregates, mitochondrial abnormalities in myopathology as well as muscle imaging findings, and serological testing for anti-cN1A antibodies.
The workshop emphasized the importance of developing IBM-specific clinical trial outcome measures accounting for the disease's natural history and the impact of therapeutic interventions. Patient testimonials highlighted the need for trials that consider the broad spectrum of IBM symptoms and their impact on quality of life.
In summary, the 272nd ENMC workshop marked a significant step forward in the understanding and diagnosis of IBM. By incorporating new diagnostic tools and creating more inclusive criteria, the revised 2024 guidelines aim to provide better support for patients and advance clinical research in IBM.
Key Points:
- The revised 2024 ENMC diagnostic criteria for incluion body myositis (IBM) are more inclusive and easier to use.
- The criteria consists of a two-step approach to improve diagnostic accuracy: Presentation Type and Investigations
- The criteria now include patients with common and uncommon presentations.
- The muscle imaging (by MRI or US), serology, and mitochondrial abnormalities in muscle biopsy have been recognized as to support diagnosis.
References:
Lilleker, J. B., Naddaf, E., Saris, C. G. J., Schmidt, J., de Visser, M., Weihl, C. C., & 272nd ENMC workshop participants (2024). 272nd ENMC international workshop: 10 Years of progress - revision of the ENMC 2013 diagnostic criteria for inclusion body myositis and clinical trial readiness. 16-18 June 2023, Hoofddorp, The Netherlands. Neuromuscular disorders : NMD, 37, 36–51. https://doi.org/10.1016/j.nmd.2024.03.001
Publish on behalf of the Scientific Panel on Clinical neurophysiology