Quantitative muscle magnetic resonance imaging as a biomarker for inclusion body myositis in clinical trials: exploring the in vivo effects of arimoclomol.

OBJECTIVES

To investigate the intramuscular effects of arimoclomol using quantitative magnetic resonance imaging (qMRI) of the thighs in a subset of inclusion body myositis (IBM) participants from a multicentre, randomised, double-blind, placebo-controlled trial, and to further evaluate the utility of qMRI assessments as outcome measures.

METHODS

Eighteen participants (10 placebo, 8 arimoclomol-treated) were recruited to undergo an MRI at baseline, 12 and 20 months. Spearman correlations between baseline clinical measures and qMRI measurements [fat fraction (FF), remaining muscle area (RMA), magnetisation transfer ratio (MTR), muscle water T2 (T2m) and fat fraction apparent (FFa)] were used to evaluate construct validity. A mixed model repeated measures (MMRM) strategy was employed to estimate mean changes, in order to determine treatment effects on qMRI biomarkers and evaluate responsiveness to disease progression over time. Longitudinal analyses examined Spearman correlations between changes in qMRI and changes in clinical assessments at the last available follow-up.

RESULTS

Baseline FF, RMA, MTR and FFa of the thigh and quadriceps demonstrated strong construct validity. No significant treatment effects on the qMRI measures were detected. FF, RMA and FFa demonstrated strong responsiveness to disease progression (standardised response means>0.8, p<0.05) at 20 months. Longitudinal changes in thigh T2m were strongly correlated with changes in myometry and modified timed up and go velocity.

CONCLUSIONS

Arimoclomol had no significant effects on the qMRI measurements evaluated, consistent with clinical outcomes from the main trial. The qMRI measurements demonstrated both validity and responsiveness, further supporting their potential utility as biomarkers in IBM.