Severe muscle damage with myofiber necrosis and macrophage infiltrates characterize anti-Mi2 positive dermatomyositis

Marco Fornaro, Francesco Girolamo, Lorenzo Cavagna, Franco Franceschini, Margherita Giannini, Angela Amati, Anna Lia, Marilina Tampoia, Dario D'Abbicco, Lorenzo Maggi, Micaela Fredi, Giovanni Zanframundo, Liala Moschetti, Laura Coladonato, Florenzo Iannone

Research output: Contribution to journalArticlepeer-review


Objective: The aim of our study was to investigate clinical and histopathological findings in adult DM patients positive for anti-Mi2 (anti-Mi2+) antibodies compared with DM patients negative for anti-Mi2 (anti-Mi2-). Methods: Clinical data of adult DM patients, who fulfilled EULAR/ACR 2017 classification criteria, were gathered from electronic medical records of three tertiary Rheumatology Units. Histopathological study was carried out on 12 anti-Mi2+ and 14 anti-Mi2- muscle biopsies performed for diagnostic purpose. Nine biopsies from immune mediated necrotizing myopathy (IMNM) patients were used as control group. Results: Twenty-two anti-Mi2+ DM [90.9% female, mean age 56.5 (15.7) years] were compared with 69 anti-Mi2- DM patients [71% female, mean age 52.4 (17) years]. Anti-Mi2+ patients presented higher levels of serum muscle enzymes than anti-Mi2- patients [median (IQR) creatine-kinase fold increment: 16 (7-37)vs 3.5 (1-9.9), P <0.001] before treatment initiation. Moreover, a trend towards less pulmonary involvement was detected in anti-Mi2+ DM (9.1% vs 30.4%, P =0.05), without any case of rapidly progressive interstitial lung disease. At muscle histology, anti-Mi2+ patients showed more necrotic/degenerative fibres than anti-Mi2- patients [mean 5.3% (5) vs 0.8% (1), P <0.01], but similar to IMNM [5.9% (6), P >0.05]. In addition, the endomysial macrophage score was similar between anti-Mi2+ and IMNM patients [mean 1.2 (0.9) vs 1.3 (0.5), P >0.05], whereas lower macrophage infiltration was found in anti-Mi2- DM [mean 0.4 (0.5), <0.01]. Conclusions: Anti-Mi2+ patients represent a specific DM subset with high muscle damage. Histological hallmarks were a higher prevalence of myofiber necrosis, endomysial involvement and macrophage infiltrates at muscle biopsy.

Original languageEnglish
Pages (from-to)2916-2926
Number of pages11
JournalRheumatology (United Kingdom)
Issue number6
Publication statusPublished - Jun 1 2021


  • antibodies
  • DM
  • muscle biopsy

ASJC Scopus subject areas

  • Rheumatology
  • Pharmacology (medical)


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