To study the potential of quantitative MRI (qMRI) fat fraction (FF) as a biomarker in nonambulant patients with Duchenne muscular dystrophy (DMD), we assessed the additive predictive value of elbow flexor FF to age at loss of hand-to-mouth movement.

Nonambulant patients with DMD (age ≥8 years) were included. Four-point Dixon MRI scans of the right upper arm were performed at baseline and at the 12-, 18-, or 24-month follow-up. Elbow flexor FFs were determined from 5 central slices. Loss of hand-to-mouth movement was determined at study visits and by phone calls every 4 months. FFs were fitted to a sigmoidal curve by use of a mixed model with random slope to predict individual trajectories. The added predictive value of elbow flexor FF to age at loss of hand-to-mouth movement was calculated from a Cox model with the predicted FF as a time-varying covariate, yielding a hazard ratio.

Forty-eight MRIs of 20 patients with DMD were included. The hazard ratio of a percent-point increase in elbow flexor FF for the time to loss of hand-to-mouth movement was 1.12 (95% confidence interval 1.04–1.21; p = 0.002). This corresponded to a 3.13-fold increase in the instantaneous risk of loss of hand-to-mouth movement in patients with a 10–percent points higher elbow flexor FF at any age.

In this prospective study, elbow flexor FF predicted loss of hand-to-mouth movement independently of age. qMRI-measured elbow flexor FF can be used as a surrogate endpoint or stratification tool for clinical trials in nonambulant patients with DMD.

This study provides Class II evidence that qMRI FF of elbow flexor muscles in patients with DMD predicts loss of hand-to-mouth movement independently of age.

为了研究定量 MRI (qMRI) 脂肪分数 (FF) 作为杜氏肌营养不良症 (DMD) 不能行走的患者生物标志物的潜力，我们评估了肘屈肌 FF 对手口运动丧失时年龄的附加预测价值。

不能行走的 DMD 患者（年龄≥8 岁）也被纳入其中。在基线和 12、18 或 24 个月随访时对右上臂进行四点 Dixon MRI 扫描。肘屈肌 FF 由 5 个中央切片确定。每 4 个月通过研究访问和电话来确定手口运动的丧失情况。通过使用具有随机斜率的混合模型将 FF 拟合到 S 形曲线以预测个体轨迹。手口运动丧失时肘屈肌 FF 对年龄的附加预测值是根据 Cox 模型计算的，其中预测的 FF 作为时变协变量，产生风险比。

纳入了 20 名 DMD 患者的 48 幅 MRI。肘屈肌 FF 增加一个百分点导致手口运动丧失的风险比为 1.12（95% 置信区间 1.04–1.21；p = 0.002 ）。这相当于任何年龄的肘屈肌 FF 高 10% 的患者，手口运动丧失的瞬时风险增加了 3.13 倍。

在这项前瞻性研究中，肘屈肌 FF 预测手口运动的丧失，与年龄无关。qMRI 测量的肘屈肌 FF 可用作非行走 DMD 患者临床试验的替代终点或分层工具。

这项研究提供了 II 类证据，表明 DMD 患者肘屈肌的 qMRI FF 可预测手口运动丧失，与年龄无关。