Update on inclusion body myositis

Irish Society for Rheumatology Autumn Meeting, Radisson Blu Hotel, Little Island, Cork, 18-19 September 2025

Prof Pedro Machado, Professor of Rheumatology and Neuromuscular Diseases, University College London (UCL) and Consultant Rheumatologist, UCL Hospitals and Northwick Park Hospital, UK, provided an update on inclusion body myositis (IBM) at the recent Irish Society for Rheumatology (ISR) Autumn Meeting. 

Prof Machado explained that IBM is an “acquired muscle disease characterised by muscle weakness and atrophy that relentlessly progresses to disability”. There is, as yet, no effective treatment. The mean time to wheelchair use in patients with IBM, which he described as a complex, rare, and debilitating disease, is 15 years.

People with IBM face a diagnostic delay of about five years. The condition is often initially misdiagnosed and is associated with significant healthcare costs. “Patients with IBM have 50 per cent more annual all-cause healthcare resource utilisation compared to non-IBM patients,” Prof Machado said. Given IBM-associated conditions, like dysphagia, pneumonia, and falls, “IBM imposes a substantial burden in terms of healthcare utilisation and associated costs,” he said.

The pathogenesis of IBM is “controversial”, he added, because it involves inflammatory and degenerative pathways, with question marks remaining around which of these elements is stronger and which is the primary cause. Prof Machado also highlighted the role of immunosenescence in IBM.

The features of IBM, he outlined, include a slow onset of proximal and distal weakness, often presenting in patients aged between 40 and 45 years. Early weakness of the finger flexors and quadriceps muscles, including loss of hand function and a propensity to fall is another feature, as well as dysphagia.

Late stage disease features include motor disability and loss of quality-of-life. The histopathology of the condition is unique, he said, as it includes inflammatory, degenerative, mitochondrial, and other elements such as atrophy, necrosis and fat replacement.

Prof Machado illustrated the pattern of IBM on MRI. He noted that MRI can be useful in monitoring disease progression. There is no way to predict how fast or slow IBM will progress in patients, he added.

Immunomodulatory therapies have so far failed as treatment options, but exercise can be helpful, Prof Machado noted.

He highlighted a randomised, controlled cross-over phase 2 trial in 2019 that found community-based aerobic exercise training is feasible and improves aerobic capacity in IBM.

Prof Machado presented studies on the use of the myostatin inhibitor bimagrumab in IBM, and noted a number of other clinical trials, including a study on the safety and efficacy of arimoclomol for IBM. The study found arimoclomol did not improve efficacy outcomes, relative to placebo, but had an acceptable safety profile in individuals with the disease.

“IBM is a complex multifactorial disease where ageing and genetic predisposition likely create the environment allowing inflammatory and degenerative muscle changes,” he said. Prof Machado added that “important progress in the understanding of IBM has been made, and the emergence of new agents targeting potential pathogenic pathways offers hope for mitigating IBM”.

The second day of the ISR meeting began with a presentation by Prof James Galloway on the topic ‘Preparing rheumatoid arthritis patients for advanced therapies – focus on infections and vaccines’. Prof Galloway is Professor of Rheumatology, King’s College London, and Honorary Consultant in Rheumatology, King’s College Hospital, UK. He spoke about when and when not to vaccinate patients with autoimmune inflammatory rheumatic diseases.

He emphasised the importance of vaccination and examined the impact of individual drugs on vaccination, highlighting the differences that exist. He pointed out that TNF-alpha inhibitors have minimal effects on the pneumococcal and seasonal flu vaccine, while anti-CD20 antibodies, such as rituximab, can result in a substantial decrease in the impact of these vaccines.