Anti-nuclear matrix protein 2 antibody-positive inflammatory myopathies represent extensive myositis without dermatomyositis-specific rash
Yuki Ichimura, Risa Konishi, Miwako Shobo, Sae Inoue, Mari Okune, Akemi Maeda, Ryota Tanaka, Noriko Kubota, Isao Matsumoto, Akiko Ishii, Akira Tamaoka, Asami Shimbo, Masaaki Mori, Tomohiro Morio, Takayuki Kishi, Takako Miyamae, Jantima Tanboon, Michio Inoue, Ichizo Nishino, Manabu Fujimoto, Toshifumi Nomura, Naoko Okiyama
Abstract
OBJECTIVES: Myositis-specific autoantibodies (MSAs) define distinct clinical subsets of idiopathic inflammatory myopathies (IIMs). The anti-nuclear matrix protein 2 (NXP2) antibody, a MSA detected in juvenile/adult IIMs, has been reported to be associated with a high risk of subcutaneous calcinosis, subcutaneous oedema and internal malignancies. The study aimed to clarify the clinical features of anti-NXP2 antibody-positive IIMs in detail. METHODS: This was a multicentre retrospective observational study on 76 anti-NXP2 antibody-positive patients. The antibody was detected via a serological assay using immunoprecipitation and western blotting. The patients were selected from 162 consecutive Japanese patients with IIMs. RESULTS: The cohort of anti-NXP2 antibody-positive IIMs included 29 juvenile patients and 47 adult patients. Twenty-seven (35.5%) patients presented with polymyositis phenotype without dermatomyositis-specific skin manifestations (heliotrope rash or Gottron sign/papules); this was more common in the adults than children (48.9% vs 15.8%, P < 0.01). Nine (11.8%) patients had subcutaneous calcinosis, and 20 (26.3%) patients had subcutaneous oedema. In addition, the proportion of patients with muscle weakness extending to the distal limbs was high (36 patients [47.4%]) in this cohort. Adult patients had a higher prevalence of malignancy than the general population (age-standardized incidence ratio of malignancies: 22.4). CONCLUSION: Anti-NXP2 antibody-positive IIMs, which include dermatomyositis sine dermatitis, are characterized by atypical skin manifestations and extensive muscular involvement.