Importance Reports on dermatomyositis (DM) sine dermatitis (DMSD) are scarce, and the concept of the disease has not been widely accepted.

Objective To confirm the existence of DMSD, determine its prevalence, and characterize its serologic features.

Design, Setting, and Participants This is a cohort study that reviewed clinical information, laboratory data, and muscle pathology slides from January 2009 to August 2019. We further assessed the follow-up data of 14 patients with DMSD. The median (interquartile range) follow-up period was 34 (16-64) months.Muscle biopsy samples, along with clinical information and laboratory data, were sent to a referral center for muscle diseases in Japan for diagnosis.Of patients whose myopathologic diagnosis was made at the National Center of Neurology and Psychiatry between January 2009 and August 2019, 199 patients were eligible for inclusion. These patients underwent full investigation for DM-specific autoantibodies (against transcriptional intermediary factor γ, Mi-2, melanoma differentiation–associated gene 5, nuclear matrix protein 2 [NXP-2], and small ubiquitin-like modifier activating enzyme ); however, 17 patients were excluded because their muscle fibers did not express myxovirus resistance protein A, a sensitive and specific marker of DM muscle pathology.

Main Outcomes and Measures Diagnosis of DMSD was based on the absence of a skin rash at the time of muscle biopsy.

Results Of the 182 patients, 93 were women (51%) and 46 were children (25%) (<18 years). Fourteen patients (8%) had DMSD and none were clinically diagnosed with DM. Among the 14 patients with DMSD, 12 (86%) were positive for anti-NXP-2 autoantibodies, while the remaining 2 were positive for anti–transcriptional intermediary factor γ and anti-Mi-2 autoantibodies, respectively. Only 28% of patients (47 of 168) with a skin rash were positive for anti-NXP-2 autoantibodies, indicating a significant association between anti-NXP-2 autoantibodies and DMSD (86% [12 of 14] vs 28% [47 of 168]; P < .001). This association was also supported by multivariable models adjusted for disease duration (odds ratio, 126.47; 95% CI, 11.42-1400.64; P < .001).

Conclusions and Relevance Dermatomyositis sine dermatitis does exist and accounts for 8% of patients with DM confirmed with muscle biopsy. Dermatomyositis sine dermatitis is significantly associated with anti-NXP-2 autoantibodies, which contrasts with anti-MDA5 DM, which is typically clinically amyopathic in presentation. It is essential to distinguish DMSD from other types of myositis because DM-specific therapies that are currently under development, including Janus kinase inhibitors, may be effective for DMSD.

关于皮肌炎（DM）的重要报告正弦皮炎（DMSD）很少，并且该疾病的概念尚未得到广泛接受。

目的 确定DMSD的存在，确定其流行程度，并表征其血清学特征。

设计，背景和参与者 这是一项队列研究，回顾了2009年1月至2019年8月的临床信息，实验室数据和肌肉病理切片。我们进一步评估了14名DMSD患者的随访数据。中位（四分位间距）随访期为34（16-64）个月。肌肉活检样本以及临床信息和实验室数据被发送到日本肌肉疾病的转诊中心进行诊断。在2009年1月至2019年8月期间在国家神经病学和精神病学中心进行肌病理学诊断的患者中，有199名患者符合纳入标准。对这些患者进行了针对DM特异性自身抗体的全面研究（针对转录中介因子γ，Mi-2，黑色素瘤分化相关基因5，核基质蛋白2 [NXP-2]和小的泛素样修饰物激活酶）；但是，有17名患者被排除在外，因为他们的肌肉纤维不表达粘液病毒抗性蛋白A，这是DM肌肉病理学的敏感和特异性标志物。

主要结果和措施 DMSD的诊断是基于肌肉活检时没有皮疹。

结果 182例患者中，女性（93岁以下）为93岁（51％），儿童为46例（25％）（<18岁）。14名患者（8％）患有DMSD，但没有临床诊断为DM。在14例DMSD患者中，有12例（86％）的抗NXP-2自身抗体呈阳性，而其余2例的抗转录中介因子γ和抗Mi-2自身抗体呈阳性。只有28％的皮疹患者（168例中的47例）抗NXP-2自身抗体呈阳性，表明抗NXP-2自身抗体与DMSD之间存在显着相关性（86％[14中的12]与28％[47] 168]；P  <.001）。调整了疾病持续时间的多变量模型也支持了这种关联（赔率，126.47； 95％CI，11.42-1400.64；P  <.001）。

结论和相关性 皮肌炎确实存在正弦皮炎，占经肌肉活检证实的DM患者的8％。皮肌炎正弦皮炎与抗NXP-2自身抗体显着相关，这与抗MDA5 DM形成鲜明对比，后者通常在临床上表现为肌病。必须将DMSD与其他类型的肌炎区分开来，因为目前正在开发的DM特异性疗法（包括Janus激酶抑制剂）可能对DMSD有效。