Clinical profile of anti-NXP-2 antibody-positive inflammatory myositis and outcome in an Indian population.

INTRODUCTION: Myositis-specific antibodies (MSA) play an important role in the clinical presentation and prognosis of patients with idiopathic inflammatory myositis (IIM). Anti-NXP-2 is one of the newly described MSA. OBJECTIVE: We aimed to describe various clinical presentations associated with anti-NXP2 antibodies and assess response to treatment. METHODS: In this retrospective study, the electronic medical records of all patients who tested positive for anti-NXP2 during June 2019 to April 2022 were screened. Details of demography, clinical presentation, and treatment data were recorded. The anti-NXP2 was tested using the Euro line test kit. Any patient who had an intensity of ≥1+ was considered testing positive. The diagnosis of IIM was reviewed after applying the 2017 European League of Rheumatology (EULAR)/American College of Rheumatology (ACR) criteria of myositis. RESULTS: Among the 660 suspected patients, 470 (71.2%) patients were positive for IIM, and 28 (5.95%) patients were positive for anti-NXP2. From anti-NXP2-antibody positive, 21/470 (4.46%) patients fulfilled criteria for IIM. Among 12 adult (57.14%) patients with IIM, 7 (58.33%) presented as polymyositis (PM) and 5 (41.6%) as dermatomyositis (DM) with median age at presentation of 45 (IQR: 25-58) years. Calcinosis and subcutaneous oedema were observed in 4 (19%) and 2 (9.52%), respectively; myalgia in 6 (28.6%); and distal muscle weakness in 5 (23.8%) patients. Malignancy at the time of diagnosis was observed in two adults with IIM (16.7%), one with DM (intraductal breast cancer), and another with PM (anaplastic large cell lymphoma). Remaining, 9 had juvenile dermatomyositis (JDM) with a median age of 4 (IQR: 3-8) years. Seven (77.8%) patients with JDM had skin rash specific for DM (heliotrope rash and Gottron's papule). None of the patients had cardiac and lung involvement, while GI symptoms, especially dysphagia, were present in 5 (23.8%) patients. During a median follow-up of 19 months (IQR: 12-26 months), 19/19 patients reported improvement and were in remission with treatment. CONCLUSION: The current study shows that adult DM patients with anti-NXP-2 autoantibodies have a unique clinical phenotype. Its presentation differs between adult and JDM, even in different parts of the world. Muscle weakness is mild and responds to treatment. Dysphagia needs more time and aggressive IS for improvement as compared to other muscle involvement. Key Points • Anti-NXP-2 antibody presentation varied from adult to child, as in different parts of the world. • In Indian adult patients, non-specific skin manifestations were more common, whereas in JDM, specific skin features were common. • There was less likely involvement of the lung and heart. But more risk of GI involvement requiring aggressive management. • Adult with anti-NXP-2 antibody should be screened for malignancy at the time of presentation.