Muscle Imaging in Inclusion Body Myositis: Refinement of MRI Criteria and Insights Into Upper Body Involvement

Area of Science:

• Neurology
• Radiology
• Medical Imaging

Background:

• Diagnosis of inclusion body myositis (IBM) is often delayed due to varied symptoms and lack of biomarkers.
• Muscle MRI is increasingly vital for diagnosis and included in international guidelines.
• This study aimed to refine MRI criteria for IBM and comprehensively assess whole-body muscle involvement.

Purpose of the Study:

• To refine Magnetic Resonance Imaging (MRI) criteria for inclusion body myositis (IBM) for improved pattern recognition and clinical applicability.
• To conduct a comprehensive whole-body muscle evaluation, including under-assessed regions.
• To identify radiological IBM phenotypes and explore clinical-radiological correlations.

Main Methods:

• Retrospective review of 68 IBM patient MRI scans and clinical records.
• Development and sensitivity assessment of new main and supportive MRI criteria for IBM.
• Semi-quantitative scoring of whole-body muscle involvement and cluster analysis for phenotype identification.

Main Results:

• Revised MRI criteria demonstrated 96% sensitivity for IBM diagnosis, robust even in atypical cases.
• Whole-body analysis revealed frequent paraspinal and neck/scapular girdle muscle wasting, with unaffected intracranial muscles.
• Significant correlation between radiological and functional involvement was found in the lower body; two distinct imaging phenotypes were identified.

Conclusions:

• Refined MRI criteria facilitate reliable IBM pattern recognition.
• Whole-body imaging provides insights into disease heterogeneity and aids patient stratification for clinical trials.
• Findings suggest potential sex-related influences on muscle vulnerability and support MRI indices as surrogate outcome measures.