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 multi-centre 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-standardised incidence ratio of malignancies: 22.4). Conclusion Anti-NXP2 antibody-positive IIMs, which include dermatomyositis sine dermatitis, are characterised by atypical skin manifestations and extensive muscular involvement.
Objective 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 edema, and internal malignancies. The study aimed to clarify the clinical features of anti-NXP2 antibody-positive IIMs in detail. Methods This multi-center 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 and 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 edema. 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.
A line blotting assay (LB) is currently used to detect myositis-specific autoantibodies (MSAs) in patients with idiopathic inflammatory myopathies (IIMs), because of its simplicity; however, the sensitivity and specificity of this assay is low. The aim of this study is to evaluate the accuracy of the commercial LB in detection of antinuclear matrix protein 2 (NXP2) antibody. Seventy-seven serum samples from patients with IIMs, in which anti-NXP2 antibodies were detected through immunoprecipitation and western blotting (IP-WB) using K562 cell lysate, were enrolled. All samples were assessed by LB and IP-WB using recombinant human NXP2 whole protein (rNXP2) produced by insect cells, and the positive rates of each assay were compared. Thirty-two samples (41.6%) showed falsenegativity by LB, which includes 11 samples with negative results by IP-WB using rNXP2.Relative intensities of IP-WB using cell lysate were significantly higher in the samples with positive results by both LB and IP-WB using rNXP2, compared to samples with positive by IP-WB using rNXP2 but negative by LB. Three of 11 samples with negative results by both LB and IP-WB using rNXP2 revealed high antibody titers. Further, differences in post-transcriptional SUMOylation were observed between recombinant and natural NXP2 proteins. In conclusion, the LB showed low sensitivity for detection of anti-NXP2 antibody, an effect exacerbated at low titers of anti-NXP2 antibodies. Moreover, there
FIGURE2. A, B, The tumor of the right index finger revealed numerous nests composed of atypical keratinocytes with invasion into the dermis and subcutaneous tissue (hematoxylin and eosin [H&E], •40 [a], •400 [b]). C, The surrounding epidermis of the tumor also showed atypical keratinocyte proliferation with hyperchromatic and clumped nuclei (HE, •200). D, HPV genotyping using the PCR-rSSO method revealing the presence of HPV-18 and HPV-45 in the lesions.
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