Inflammatory myopathies with anti-Ku antibodies: a prognosis dependent on associated lung disease

Anti-Ku antibodies have been reported in a wide spectrum of autoimmune diseases, sometimes in association with inflammatory myopathies (IM). We studied the clinical, laboratory, and muscle histologic features of all anti-Ku-positive patients detected in our hospital during the last 10 years, as well as their treatment and outcomes. Anti-Ku antibodies were found in 34 patients (0.46% of 20,600 sera positive for antinuclear antibodies), and complete data were available for 30 patients; 86.7% were female, mean age was 49 years (range, 20-73 yr). The most frequent clinical manifestations were arthralgia (77%) and Raynaud phenomenon (53%). Eleven (37%) patients had IM, 8 of them as part of an overlap syndrome defined as IM associated with connective autoimmune disease (5 systemic sclerosis [SSc], 2 Sjögren syndrome (SS), and 1 systemic lupus erythematosus [SLE]). Of 21 patients without IM, 19 had autoimmune diseases (including 6 SLE, 2 SSc, 2 SS, and 2 rheumatoid arthritis), 1 had bronchial neoplasia, and 1 had nephroangiosclerosis. Clinical features of the 9 patients with IM were myalgia (91%), proximal muscle weakness (89%), and dysphagia (36%). All had increased creatine kinase (median, 2210 U/L; range, 194-4073 U/L). Muscle biopsy showed necrosis, inflammation, and positive HLA class I immunostaining. Interstitial lung disease (ILD) was detected on computed tomography (CT) scan in 11 patients (37%) and was significantly more frequent in patients with IM (82% vs. 10.5%, p < 0.001). Fourteen (47%) patients required no immunosuppressive treatment or only a low corticosteroid dose (<15 mg/d, n = 3). A high dose of corticosteroids was more frequently administered in patients with IM (10/11 cases, 80% with associated ILD) than in patients without IM (4/19 cases, 0 with ILD). Complete muscle remission after steroids occurred in 73% of patients with IM. Lung disease was corticoresistant in 6 of 8 (75%) treated cases.Anti-Ku antibodies remain rarely detected, but their presence can be frequently associated with corticosensitive IM and severe, corticoresistant ILD.