OBJECTIVES Juvenile localized scleroderma (JLS) is a rare chronic autoimmune disease which can also affect bones and muscles. Nevertheless, muscle loss was not previously investigated in patients with JLS. Thus, the aim of this study was to retrospectively evaluate deep involvement and assess and quantify sarcopenia in JLS patients using magnetic resonance imaging (MRI). METHODS Fourteen children with JLS (nine females, mean age ± SD, 7.1 ± 3.6 years) referring to our tertiary center from January 2012 to January 2018 who underwent at least one MRI examination including axial T1-weighted and short tau inversion recovery images were included. Two readers assessed in consensus superficial and deep involvement. Muscle edema, muscle fatty infiltration, and sarcopenia were independently scored (absent, moderate, or severe) and the Cohen's kappa coefficient computed. Skin perimeter, subcutaneous area, muscle area, and muscle volume were independently measured using the contralateral unaffected extremity as reference (paired Student's t test, p < 0.05). The intraclass correlation coefficient (ICC) was used to investigate the reliability of the measurements. RESULTS All patients showed superficial involvement with subcutaneous fat atrophy being the most common finding (13 patients). Bone marrow edema occurred in five patients. Muscle edema affected ten children (moderate in seven, severe in three; k = 0.89), muscle fatty replacement occurred in one case (severe; k = 1.00), and sarcopenia was detected in eight patients (severe in two; k = 0.78). All quantitative parameters were lower on the affected side than on the unaffected contralateral limb (p < 0.05, each) and all measurements showed a high reliability (ICC > 0.750, each). CONCLUSION Patients with JLS can be affected by sarcopenia and quantitative analyses allow a robust characterization of such finding. KEY POINTS • Deep involvement in juvenile localized scleroderma is frequently characterized by sarcopenia. • In juvenile localized scleroderma, muscle edema and sarcopenia are mostly moderate while fatty infiltration, even if rare, can be severe. • Sarcopenia can be reliably quantified in children with juvenile localized scleroderma using MRI.

中文翻译：

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青少年局部硬皮病中的少肌症：关于深度受累的新见解。

目的青少年局部硬皮病（JLS）是一种罕见的慢性自身免疫性疾病，也可影响骨骼和肌肉。尽管如此，先前尚未对JLS患者进行肌肉损失调查。因此，本研究的目的是使用磁共振成像（MRI）回顾性评估JLS患者的深度受累并评估和量化肌肉减少症。方法包括14位JLS儿童（9名女性，平均年龄±SD，7.1±3.6岁），这些患者是我们2012年1月至2018年1月的三级中心，接受了至少一次MRI检查，包括轴向T1加权和短tau倒置恢复图像。 。两位读者一致评估了肤浅和深入的参与。分别对肌肉水肿，肌肉脂肪浸润和肌肉减少症进行评分（不存在，中度或严重），并且Cohen' 计算出的卡伯系数。皮肤周长，皮下面积，肌肉面积和肌肉体积均以对侧未患肢为参考独立测量（配对的t检验，p <0.05）。组内相关系数（ICC）用于研究测量的可靠性。结果所有患者均表现为浅表累及皮下脂肪萎缩（13例）。五例患者发生了骨髓水肿。肌肉水肿影响了10名儿童（中度7例，重度3例; k = 0.89），其中1例发生了肌肉脂肪替代（严重; k = 1.00），并且8例患者出现肌肉减少症（2例; k = 0.78） 。患侧的所有定量参数均低于未患侧对侧肢体（p <0.05，），所有测量结果均显示出很高的可靠性（ICC> 0.750）。结论JLS患者可能会受到肌肉减少症的影响，定量分析可以对这种发现进行可靠的描述。要点•深度参与青少年局部性硬皮病的特征通常是肌肉减少症。•在少年性硬皮病中，肌肉水肿和肌肉减少症大多为中度，而脂肪浸润（即使罕见）也可能很严重。•使用MRI可以可靠地量化青少年局限性硬皮病患儿的少肌症。要点•深度参与青少年局部性硬皮病的特征通常是肌肉减少症。•在少年性局部硬皮病中，肌肉水肿和肌肉减少症大多为中度，而脂肪浸润（即使罕见）也可能很严重。•使用MRI可以可靠地量化青少年局限性硬皮病患儿的少肌症。要点•深度参与青少年局部性硬皮病的特征通常是肌肉减少症。•在少年性硬皮病中，肌肉水肿和肌肉减少症大多为中度，而脂肪浸润（即使罕见）也可能很严重。•使用MRI可以可靠地量化青少年局限性硬皮病患儿的少肌症。