Assessing the sensitivity and specificity of myositis-specific and associated autoantibodies: a sub-study from the MyoCite cohort

Pulmonary fibrosis as the sole manifestation of anti-Ku antibody positivity in the absence of myositis: A case report

Background

Anti-Ku antibodies are autoantibodies directed against the Ku protein complex involved in DNA repair. They are typically associated with overlap syndromes featuring polymyositis and systemic sclerosis. Isolated pulmonary involvement without myositis is exceedingly rare.

Case presentation

We report the case of a 70-year-old male, a former smoker with an 18-year smoking history who quit 20 years ago, presenting with a one-year history of progressive dyspnea and dry cough. High-resolution computed tomography (HRCT) revealed pulmonary fibrosis with areas of ground-glass opacities. Laboratory tests showed antinuclear antibodies at a titer of 1:2560 with a speckled pattern and positivity for anti-Ku antibodies. Creatine phosphokinase levels were within normal limits. There were no clinical signs of myositis, myalgia, skin manifestations, or Raynaud's phenomenon.

Conclusion

This case underscores the rarity of pulmonary fibrosis as the sole clinical manifestation associated with anti-Ku antibody positivity in the absence of myositis. Clinicians should consider testing for anti-Ku antibodies in patients with idiopathic interstitial lung disease, even when muscular and cutaneous symptoms are absent.

Autoantibody testing in myositis: an update

PURPOSE OF REVIEW

This review aims to provide an update on myositis autoantibody testing strategies. We have focussed on the reliability and usefulness of different myositis autoantibody detection methods, including commonly used solid phase immunoassays and newer discovery techniques.

RECENT FINDINGS

Several studies have highlighted the limitations of currently available immunoassays, particularly when used in populations with low pretest probability and without supporting clinical evidence. While many autoantibodies, such as anti-Jo1, are detected with high sensitivity and specificity, the low incidence of myositis autoantibodies in tested populations reduces their positive predictive value. The low sensitivity of line immunoassays to detect key myositis autoantibodies, including anti-TIF1γ and rarer antisynthetase autoantibodies, is a concern.

SUMMARY

Myositis autoantibodies are widely accepted as important clinical tools, and hence, there is a significant demand for reliable, accessible, and affordable detection methods. False positives and negative results have the potential to impact on patient care, particularly for malignancy and lung disease associated autoantibodies. Increased availability of myositis autoantibody testing has led to a rise in requests from a broader range of clinicians. It is critically important that clinicians are aware of specific limitations of tests and interpret results in the context of clinical findings.