Aims: Edema of the limbs is uncommon in idiopathic inflammatory myopathies (IIM). The few reported cases have been associated with severe and refractory dermatomyositis (DM), sometimes in association with cancers. We aimed to determine if edematous myositis is a homogeneous subtype based on clinical, serological and pathological features. Methods: This is a retrospective observational study performed between 2008 and 2015 in the French national referral center for myositis. All adult patients with an inflammatory muscle biopsy and upper limbs edema were included as well as IIM cases without limb edema as controls. Clinical, biological and pathological features were collected. Results: Seventeen edematous myositis were included and compared to 174 IIM without edema, including 50 DM controls. Edema was the first manifestation in 23% of patients. Muscle weakness was severe and symmetric, 71% of patients presented dysphagia and a restrictive ventilatory pattern was found in 40%. Fifty‐two percent of patients had a typical DM skin rash and 23% had cancer within 3 years of diagnosing myositis. Fifty‐three percent of patients presented a myositis specific antibody and only DM‐specific antibodies were detected. Classic pathological DM features (perifascicular atrophy, perifascicular/perimysial perivascular inflammation) were uncommon but capillary C5b‐9 deposition and MxA expression were seen in 79% and 73% of cases, respectively. A perimysial edema was found in 82% of cases. Seventeen percent of patients died (median follow up of 18 months). Edematous myositis demonstrated more marked capillary C5b‐9 deposition compared to IIM controls. There was no clinical, biological or pathological difference with DM controls except for limb edema. Conclusion: Our study underlines that limb edema could be a symptom of IIM and that edematous myositis are mostly DM. The vasculopathy seems to play a key role in its pathophysiology. Limb edema associated with muscle impairment should suggest the diagnosis of DM in clinical settings.

中文翻译：

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水肿性肌炎：首先提示皮肌炎诊断的临床表现。

目的：四肢水肿在特发性炎症性肌病 (IIM) 中并不常见。少数报道的病例与严重和难治性皮肌炎 (DM) 有关，有时与癌症有关。我们旨在根据临床、血清学和病理学特征确定水肿性肌炎是否是同种亚型。方法：这是 2008 年至 2015 年在法国国家肌炎转诊中心进行的一项回顾性观察研究。包括所有具有炎性肌肉活检和上肢水肿的成年患者以及没有肢体水肿的 IIM 病例作为对照。收集临床、生物学和病理学特征。结果：包括 17 例水肿性肌炎，并与 174 例无水肿的 IIM（包括 50 例 DM 对照）进行比较。水肿是 23% 患者的首发表现。肌肉无力严重且对称，71% 的患者出现吞咽困难，40% 的患者出现限制性通气模式。52% 的患者在诊断出肌炎后 3 年内出现典型的 DM 皮疹，23% 的患者出现癌症。53% 的患者出现肌炎特异性抗体，仅检测到 DM 特异性抗体。经典病理 DM 特征（束周萎缩、束周/肌周血管周围炎症）并不常见，但分别在 79% 和 73% 的病例中观察到毛细血管 C5b-9 沉积和 MxA 表达。在 82% 的病例中发现了肌周水肿。17% 的患者死亡（中位随访时间为 18 个月）。与 IIM 对照相比，水肿性肌炎表现出更明显的毛细血管 C5b-9 沉积。除了肢体水肿外，与DM对照没有临床、生物学或病理学差异。结论：我们的研究强调肢体水肿可能是 IIM 的症状，水肿性肌炎主要是 DM。血管病变似乎在其病理生理学中起关键作用。与肌肉损伤相关的肢体水肿应提示临床诊断 DM。