Background/Purpose: Anti-Ku antibodies (Abs) were initially described in patients with polymyositis and scleroderma. Subsequently, an association has been demonstrated with other systemic autoimmune diseases (SADs), particularly overlap syndromes. However, controversies exist regarding their clinical significance and their relationship with SADs or some of their manifestations. Objective: To describe the clinical and immunological characteristics of a case series of patients with positive anti-Ku antibodies.

Methods: Descriptive study of a cohort of patients from a university hospital with positive anti-Ku antibodies between 2017 and 2022. Clinical variables (Raynaud’s phenomenon, arthritis, arthralgia, myalgia, muscle weakness, dyspnea, dysphagia, diffuse interstitial lung disease (DILD)), complementary investigations (pulmonary function tests (PFTs), high-resolution computed tomography (HRCT), capillaroscopy), and autoimmune study (ANA ENA, anti-DNA, complement study, anti-PM scl 75 antibodies, anti-PM scl 100 antibodies, CENP-B, antiphospholipid antibodies, rheumatoid factor (RF), and anti-citrullinated peptide antibodies (ACPA)) were analyzed. Finally, clinical diagnostic orientation, diagnosis based on systemic autoimmune disease (SAD) criteria, or final diagnosis of non-SAD pathologies were recorded.

Results: A total of 17 patients positive for anti-Ku antibodies were identified, of whom 14 were women (82.4%) with a mean age of 57 years and a median follow-up of 43 months. The clinical manifestations presented were as follows: arthralgia (13; 76.5%), arthritis (8; 47.1%), myalgia (6; 35.3%), myositis (2; 11.8%), muscle weakness (2; 11.8%), dysphagia (1; 5.9%), dyspnea (4; 23.5%), and Raynaud’s phenomenon (3; 17.6%). All patients had positive ANA, of which 8 cases (47.1%) exhibited a nucleolar pattern, 8 cases (47.1%) showed a fine speckled pattern, and only 1 case had a centromeric dot-like pattern. A total of 8 patients underwent high-resolution computed tomography (HRCT), of which 2 cases (25%) presented a ground-glass opacities pattern, 2 cases (25%) had pulmonary thromboembolism, and 2 cases (25%) had one or multiple neoplastic pulmonary nodules. Pulmonary function tests (PFTs) were performed in 7 cases, with 3 cases (42.9%) showing normal results, 2 cases (28.6%) displaying an obstructive pattern, and 2 cases (28.6%) demonstrating a restrictive pattern. Capillaroscopy was performed on 4 patients (3 normal results, 1 non-specific pattern). A diagnosis of neoplasia was established in 5 cases (29.4%). Only 6 patients (35.3%) met the criteria for systemic autoimmune disease (SAD), including 3 cases of systemic lupus erythematosus (one of them with associated antiphospholipid syndrome), 2 cases of Sjögren’s syndrome, and 1 case of systemic sclerosis.

Conclusion: In our case series, the clinical and laboratory characteristics were highly heterogeneous. The presence of anti-Ku antibodies was associated with the diagnosis of a systemic autoimmune disease (SAD) in just over one-third of the cases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/anti-ku-antibodies-a-case-series/