Quantitative Muscle Magnetic Resonance Imaging Demonstrates Resolution of Muscle Edema in Refractory Dermatomyositis: A Post Hoc Analysis of a Proof-of-Concept Clinical Trial of Tofacitinib.

OBJECTIVE

To evaluate changes in muscle edema using short-tau inversion recovery (STIR) imaging and quantitative diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) mapping in patients with refractory dermatomyositis (DM) treated with tofacitinib.

METHODS

This post hoc imaging analysis included patients from a 12-week, open-label trial of tofacitinib 11 mg daily in refractory DM. Bilateral thigh magnetic resonance imaging was obtained at baseline and week 12 using standardized STIR, T1-weighted, and DWI sequences. Muscle edema (ME) and fascial edema were assessed qualitatively on STIR imaging. ADC values were measured in muscles demonstrating baseline STIR hyperintensity using three nonoverlapping regions of interest per muscle. Clinical outcomes included Manual Muscle Testing of eight muscle groups (MMT-8).

RESULTS

Ten patients completed the study. Baseline ME was present in 32 of 320 thigh muscles (10%) across four patients. Quantitative ADC analysis, performed in the 32 edematous muscles, demonstrated significant decreases in tissue diffusivity in 11 muscles (34.5%), including the rectus femoris, vastus lateralis, vastus medialis, sartorius, gracilis, and adductors. Absolute ADC reductions ranged from -0.18 to -0.37 × 10-3 mm2/s. Two patients with baseline proximal weakness showed parallel improvement in MMT-8 scores and ADC values, whereas two patients with normal strength showed subclinical ADC improvement.

CONCLUSION

Tofacitinib resulted in marked clinical and radiologic improvement in refractory DM. Quantitative ADC mapping detected resolution of muscle inflammation, including subclinical improvement not evident on strength or enzyme testing. ADC metrics may serve as objective imaging biomarkers of treatment response in DM.