P118 Calcinosis in adult dermatomyositis: association with anti-NXP2 antibodies and distinct anatomical distribution

Abstract

Calcinosis cutis, the deposition of calcium apatite in skin and soft tissues, affects 20% of adults with dermatomyositis (DM) and 40% of children with DM (juvenile DM). Calcinosis lesions present as hard papules, nodules or plaques and cause both pain and functional impairment. Calcinosis in juvenile DM has been studied in depth, but it has received little research attention in the adult population with DM. Our aim was to evaluate the prevalence, clinical presentation and associated features of calcinosis in adult patients with DM. A prospective study conducted from April 2019 to December 2024 at a regional dermatomyositis service examined the presence of calcinosis in 191 adult patients with DM. Patients underwent clinical evaluation by dermatology and rheumatology consultants; calcinosis was identified via clinical examination and imaging (plain radiographs, computed tomography and magnetic resonance imaging). The extent of calcinosis was mapped anatomically and its presence aligned with myositis-specific antibodies and extracutaneous clinical features. Statistical analysis was performed using Fisher’s exact test. Calcinosis was observed in 15 of 191 (7.9%) adult patients with DM. The most significant association was found with the NXP2 antibody, where 42% of NXP2-positive patients had calcinosis (P = 0.001). The thighs were the most commonly affected area (87%), followed by lower torso/buttocks (60%) and upper limbs (40%). No significant association between calcinosis and extracutaneous clinical manifestations (including myositis, malignancy, dysphagia and interstitial lung disease) was found. Calcinosis in adult DM is strongly associated with NXP2 antibodies and primarily affects the thighs and lower torso. Our study helps to define the adult DM–calcinosis subgroup. Delineation of this phenotype is important for prognosis and provides a key target for future therapeutic strategies.