Maria Casal-Dominguez1, Iago Pinal-Fernandez2, Assia Derfoul3, Rose Graf3, Harlan Michelle4, Jemima Albayda4, Eleni Tiniakou4, Brittany Adler4, Sonye K Danoff4, Thomas E Lloyd4, Lisa Christoper-Stine4, Julie J Paik4, Andrew L Mammen5. 1. Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD USA; Johns Hopkins University School of Medicine, Baltimore, Maryland USA. Electronic address: maria.casal-dominguez@nih.gov. 2. Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD USA; Johns Hopkins University School of Medicine, Baltimore, Maryland USA; Faculty of Health Sciences and Faculty of Computer Science, Multimedia and Telecommunications, Universitat Oberta de Catalunya, Barcelona, Spain. 3. Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD USA. 4. Johns Hopkins University School of Medicine, Baltimore, Maryland USA. 5. Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD USA; Johns Hopkins University School of Medicine, Baltimore, Maryland USA. Electronic address: andrew.mammen@nih.gov.
Abstract
OBJECTIVES: To define the clinical features of anti-Ku-positive myositis patients and to determine the reliability of the Euroline assay to detect anti-Ku autoantibodies. METHODS: Serum samples were screened for anti-Ku autoantibodies by Euroline and positive samples were confirmed by ELISA. The prevalence and severity of clinical features at onset and during follow-up in patients with anti-Ku-positive myositis were compared to those with dermatomyositis, immune-mediated necrotizing myopathy (IMNM), the antisynthetase syndrome (AS), inclusion body myositis (IBM), anti-U1-RNP-positive myositis, and anti-PM/Scl-positive myositis. RESULTS: 72 (2.9%) of 2475 samples were anti-Ku positive by Euroline using the manufacturer's recommended cutoff of >15. Just 17 (23.6%) of these were confirmed by ELISA and considered anti-Ku-positive for the analysis. Comparators included 169 IMNM, 168 AS, 387 IBM, 20 anti-U1-RNP-positive, and 47 anti-PM/Scl-positive patients. Muscle weakness was a presenting feature in 38% of anti-Ku-positive patients; 81% developed weakness during follow-up. Anti-Ku-positive patients had increased distal weakness compared to the non-IBM comparators. Interstitial lung disease (ILD) was present in 19% of anti-Ku-positive patients at the first visit and eventually developed in 56% of them. Throughout the course of disease, Gottron's papules and/or heliotrope rashes were less common in anti-Ku-positive patients (19%) compared to those with dermatomyositis (94%) or anti-PM/Scl-positive myositis (89%). Anti-Ku-positive patients never developed calcinosis. CONCLUSIONS: The phenotype of anti-Ku positive myositis is distinguished by distal weakness, frequent ILD, infrequent rash, and no calcinosis. When used according to the current manufacturer's instructions, the Euroline assay has a high false-positive rate for anti-Ku autoantibodies. Published by Elsevier Inc.
OBJECTIVES: To define the clinical features of anti-Ku-positive myositis patients and to determine the reliability of the Euroline assay to detect anti-Ku autoantibodies. METHODS: Serum samples were screened for anti-Ku autoantibodies by Euroline and positive samples were confirmed by ELISA. The prevalence and severity of clinical features at onset and during follow-up in patients with anti-Ku-positive myositis were compared to those with dermatomyositis, immune-mediated necrotizing myopathy (IMNM), the antisynthetase syndrome (AS), inclusion body myositis (IBM), anti-U1-RNP-positive myositis, and anti-PM/Scl-positive myositis. RESULTS: 72 (2.9%) of 2475 samples were anti-Ku positive by Euroline using the manufacturer's recommended cutoff of >15. Just 17 (23.6%) of these were confirmed by ELISA and considered anti-Ku-positive for the analysis. Comparators included 169 IMNM, 168 AS, 387 IBM, 20 anti-U1-RNP-positive, and 47 anti-PM/Scl-positive patients. Muscle weakness was a presenting feature in 38% of anti-Ku-positive patients; 81% developed weakness during follow-up. Anti-Ku-positive patients had increased distal weakness compared to the non-IBM comparators. Interstitial lung disease (ILD) was present in 19% of anti-Ku-positive patients at the first visit and eventually developed in 56% of them. Throughout the course of disease, Gottron's papules and/or heliotrope rashes were less common in anti-Ku-positive patients (19%) compared to those with dermatomyositis (94%) or anti-PM/Scl-positive myositis (89%). Anti-Ku-positive patients never developed calcinosis. CONCLUSIONS: The phenotype of anti-Ku positive myositis is distinguished by distal weakness, frequent ILD, infrequent rash, and no calcinosis. When used according to the current manufacturer's instructions, the Euroline assay has a high false-positive rate for anti-Ku autoantibodies. Published by Elsevier Inc.
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