Abstract 4368721: Myocardial Inflammation and Complete Heart Block in Anti-NXP-2 Dermatomyositis: An Unrecognized Cardiac Manifestation

Introduction: Dermatomyositis (DM) is a rare autoimmune myopathy with multisystem involvement including skin and skeletal muscle. Cardiac conduction abnormalities are rarely reported in DM and polymyositis, with only a few documented cases. Data linking specific autoantibodies to cardiac involvement is limited. We report the first case of complete heart block (CHB) in a patient with anti-NXP-2 positive DM. Case Description: A 68-year-old man with chronic obstructive pulmonary disease and alcohol use disorder presented with one month of progressive proximal muscle weakness, papular rash with areas of erythema and healing ulcers over the trunk and extremities, and dysphagia. During evaluation, he developed CHB with bradycardia (heart rate 20-30), requiring emergent transvenous pacing. Shortly after placement, he recovered to stable 1:1 atrioventricular conduction with a right bundle branch block and a left anterior fascicular block, without recurrence or further need for pacing. Echocardiography showed mildly reduced ejection fraction; coronary angiography was non-obstructive. Cardiac MRI revealed normal ventricular morphology with diffusely elevated T1 values, mildly increased T2 signal in the septum, and a mildly elevated extracellular volume—findings consistent with diffuse myocardial inflammation (Figure 1). Laboratory tests revealed troponin 114 ng/L, aldolase 176 U/L, creatine kinase 9,916 U/L, C-reactive protein 11 mg/dL, and anti-nuclear antibody 1:320 (centromere pattern); myositis panel was positive for anti-NXP-2 antibodies. Electromyography confirmed myopathy. Muscle biopsy revealed chronic active necrotizing myopathy with perifascicular atrophy (Figure 2); skin biopsy showed leukocytoclastic vasculitis (Figure 3). High-dose steroids were initiated and given the uncertain natural history of CHB in this rare subset, a shared decision was made to implant a leadless Medtronic Micra™ AV pacemaker. Further abdominal imaging revealed a small pancreatic head lesion; outpatient malignancy workup is ongoing. Discussion: This first documented case of CHB in anti-NXP-2 DM suggests a rare and underrecognized cardiac manifestation of this antibody subset. It supports prior histopathologic evidence of conduction system inflammation in inflammatory myopathies and underscores the importance of cardiac surveillance and multidisciplinary care. Further studies are needed to define the prevalence and clinical impact of cardiac involvement across DM serologic subsets.