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.

Dermatomyositis, an idiopathic inflammatory myopathy, is characterized by cutaneous itchy manifestations, which are frequently refractory and recurrent even after intensive immunosuppressive treatments. To evaluate the effectiveness and safety of apremilast, an oral phosphodiesterase 4 inhibitor, in treating skin‐dominant dermatomyositis in which myositis and interstitial lung disease are absent or in remission, we performed this prospective, single‐arm, interventional study. A total of five Japanese patients (one male and four females, median [range] age, 64 [37–71] years) with refractory dermatomyositis‐associated cutaneous manifestations were recruited and treated with a 12‐week course of oral apremilast. Among five enrolled patients, three experienced diarrhea with full‐dose apremilast (30 mg twice daily), two of whom withdrew from the study and recovered quickly afterwards. A total of three evaluable female patients (median [range] age, 65 [64–71] years) received apremilast treatment for 12 weeks. A 39.4% reduction from baseline Cutaneous Dermatomyositis Disease Area and Severity Index total activity score, but not the damage score, at week 12 was observed in all three patients. Visual analog scale of itching, and quality of life by Dermatology Life Quality Index were slightly improved in one and two apremilast‐treated patients, respectively. As apremilast was effective, with expected and recoverable digestive adverse events (diarrhea), in patients with refractory and recurrent dermatomyositis‐associated cutaneous manifestations in this first phase Ib study, it can be suggested as a possible treatment when aggressive immunosuppressive therapies with high‐dose systemic corticosteroid and/or immunosuppressive agents for other manifestations, myositis, and interstitial lung disease, are not required.

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