The phenotype of myositis patients with anti-Ku autoantibodies

Maria Casal-Dominguez, Iago Pinal-Fernandez, Assia Derfoul, Rose Graf, Harlan Michelle, Jemima Albayda, Eleni Tiniakou, Brittany Adler, Sonye K. Danoff, Thomas E. Lloyd, Lisa Christoper-Stine, Julie J. Paik, Andrew L. Mammen

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Pages (from-to)728-734
Number of pages7
JournalSeminars in Arthritis and Rheumatism
Issue number4
StatePublished - Aug 2021


  • Elisa
  • Euroline
  • Myositis
  • anti-Ku

ASJC Scopus subject areas

  • Rheumatology
  • Anesthesiology and Pain Medicine


Dive into the research topics of 'The phenotype of myositis patients with anti-Ku autoantibodies'. Together they form a unique fingerprint.

Cite this