Quantitative muscle MRI in sporadic inclusion body myositis (sIBM): A prospective cohort study

Abstract

Background: Sporadic inclusion body myositis (sIBM) is the predominant idiopathic inflammatory myopathy (IIM) in older people. Limitations of classical clinical assessments have been discussed as possible explanations for failed clinical trials, underlining the need for more sensitive outcome measures. Quantitative muscle MRI (qMRI) is a promising candidate for evaluating and monitoring sIBM.

Objective: Longitudinal assessment of qMRI in sIBM patients.

Methods: We evaluated fifteen lower extremity muscles of 12 sIBM patients (5 females, mean age 69.6, BMI 27.8) and 12 healthy age- and gender-matched controls. Seven patients and matched controls underwent a follow-up evaluation after one year. Clinical assessment included testing for muscle strength with Quick Motor Function Measure (QMFM), IBM functional rating scale (IBM-FRS), and gait analysis (6-minute walking distance). 3T-MRI scans of the lower extremities were performed, including a Dixon-based sequence, T2 mapping and Diffusion Tensor Imaging. The qMRI-values fat-fraction (FF), water T2 relaxation time (wT2), fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (λ1), and radial diffusivity (RD) were analysed.

Results: Compared to healthy controls, significant differences for all qMRI parameters averaged over all muscles were found in sIBM using a MANOVA (p < 0.001). In low-fat muscles (FF < 10%), a significant increase of wT2 and FA with an accompanying decrease of MD, λ1, and RD was observed (p≤0.020). The highest correlation with clinical assessments was found for wT2 values in thigh muscles (r≤-0.634). Significant changes of FF (+3.0%), wT2 (+0.6 ms), MD (-0.04 10-3mm2/s), λ1 (-0.05 10-3mm2/s), and RD (-0.03 10-3mm2/s) were observed in the longitudinal evaluation of sIBM patients (p≤0.001). FA showed no significant change (p = 0.242).

Conclusion: qMRI metrics correlate with clinical findings and can reflect different ongoing pathophysiological mechanisms. While wT2 is an emerging marker of disease activity, the role of diffusion metrics, possibly reflecting changes in fibre size and intracellular deposits, remains subject to further investigations.

Keywords: Diffusion tensor imaging; fat fraction; quantitative muscle MRI; sporadic inclusion body myositis; water T2 relaxation time.

Fig. 1

Flowchart of study procedure.

Fig. 2

Overview of parameter maps for fat fraction (FF), water T2 relaxation time (T2), fractional anisotropy (FA), and mean diffusivity (MD) of representative sporadic inclusion body myositis patient (sIBM) and healthy control (HC).

Fig. 3

Overview of segmented muscles and corresponding muscle groups in a representative participant (A – cross-sectional; B – side view, C – front and back view). Bar plots show mean qMRI metrics for patients with sporadic inclusion body myositis (sIBM) and control group (D). The lines show the 95% -interval of confidence. *adjusted p < 0.05. BF = biceps femoris; ED = extensor digitorum longus; GM = gastrocnemius medialis; GL = gastrocnemius lateralis; GR = gracilis; PE = peroneal group; RF = rectus femoris; SA = sartorius; SO = soleus; SM = semimembranosus; ST = semitendinosus; TA = tibialis anterior; TP = tibialis posterior; VL = vastus lateralis; VM = vastus medialis.

Fig. 4

Overview of mean qMRI metrics low-fat muscles (FF < 10%) for the different muscle groups of patients with sporadic inclusion body myositis (sIBM) and control group. The lines show the 95% -interval of confidence. *adjusted p < 0.05.

Fig. 5

Fat fraction (FF) maps of a representative patient with sporadic inclusion body myositis (sIBM) at baseline and follow-up (A). Bar plots showing the relative mean changes of qMRI metrics in IBM patients between baseline and follow-up, normalized to the mean of both measurements. *adjusted p < 0.05.