Muscle Ultrasound in Inclusion Body Myositis: Integrating Qualitative and Quantitative Approaches With Clinical and <scp>MRI</scp> Findings

INTRODUCTION/AIMS: Inclusion body myositis (IBM) is an inflammatory myopathy with an insidious onset, often making diagnosis challenging. Although neuroimaging has recently been included in diagnostic criteria, the role of muscle ultrasound-despite being a rapid and cost-effective tool-in IBM has been less extensively characterized. In this study, we aimed to explore whether qualitative and quantitative muscle ultrasound measures reflect the pattern of muscle involvement in IBM and are associated with magnetic resonance imaging (MRI) findings. METHODS: Thirteen patients with histologically confirmed IBM underwent clinical evaluation, including the IBM Functional Rating Scale (IBM-FRS) and Medical Research Council (MRC) grading. Qualitative (Heckmatt scale, from 1 to 4) and quantitative (muscle echo-intensity and thickness z-scores) ultrasound assessments were performed on fourteen muscles bilaterally. Lower limb muscle MRI was conducted using T1-weighted (with Mercuri score) and STIR sequences. Correlations between ultrasound parameters and MRI findings were analyzed. RESULTS: Qualitative ultrasound assessment showed increased echogenicity, mainly in flexor digitorum profundus, vastus lateralis, rectus femoris, tibialis anterior, and medial gastrocnemius. Quantitative analysis confirmed elevated echo-intensity in these muscles, with milder involvement of tibialis anterior and lateral gastrocnemius. Both qualitative Heckmatt scores and quantitative muscle echo-intensity scores showed positive associations with MRI T1 Mercuri scores (p < 0.001). DISCUSSION: In this study, both qualitative and quantitative muscle ultrasound reflected the characteristic pattern of muscle involvement in IBM and showed associations with MRI findings, supporting their utility in describing the pattern and extent of muscle damage.