Background Interstitial lung disease (ILD) is a common complication of polymyositis/dermatomyositis (PM/DM). It is often lethal if it occurs as a rapidly progressive pattern especially in patients present as clinically amyopathic dermatomyositis (CADM), a unique subtype of DM frequently seen in East Asia populations. Anti-MDA5 antibody (also known as anti-CADM140 antibody) has been associated with this severe clinical entity in Japanese population , while the clinical utility of this autoantibody remains unclear in Chinese patients.
Objectives The purpose of this study was to investigate the diagnostic and prognostic significance of anti-MDA5 antibody in Chinese PM/DM patients.
Methods A total of 64 PM/DM patients (including 9 CADM patients, 34 classic DM patients, and 21 polymyositis patients), 16 idiopathic pulmonary fibrosis (IPF) patients, and 10 normal controls were recruited from the affiliated Drum Tower Hospital, Nanjing University Medical School, China. The diagnosis was based on the Bohan and Peter criteria for PM/DM . Information on all hospitalizations was obtained from electronic medical records. Serum anti-MDA5 antibody titer was measured using an ELISA method described previously . The clinical features, laboratory findings, and prognosis were compared.
Results A total of 9 (100%) CADM patients, 17 (50%) classic DM patients and 1 (6.3%) IPF patient were identified as anti-MDA5 antibody positive. Anti-MDA5 antibody was more prevalence in PM/DM with ILD patients than in PM/DM without ILD patients (54.2% vs 0%, P<0.0001 by Fisher’s exact test). Comparing with the PM/DM patients negative for anti-MDA5 antibody, there were higher prevalence of cutaneous manifestations (100% vs 39.5%, P <0.0001), higher frequency of ILD (100% vs 57.9%, P<0.0001), higher frequency of rapidly progressive ILD (34.6% vs 2.6%, P =0.0008), but lower levels for creatine phosphokinase (CK) and CK-MB (P =0.003 and P =0.008, respectively), lower positive rate for anti-nuclear antibody (37.5% vs 80%, P =0.002) in patients with anti-MDA5 antibody. 7 of 26 patients positive for anti-MDA5 antibody, but no patient negative for anti-MDA5 antibody, died from respiratory failure within 12 months after the disease onset. The mortality rate for patients with anti-MDA5 antibody was significantly higher than that for patients without anti-MDA5 antibody (P=0.026). Especially, anti-MDA5 antibody was associated with DM complicated ILD but not with other PM/DM patients in Chinese, with a sensitivity of 72.2% (26/36) and a specificity of 100% (28/28).
Conclusions Unlike in Japanese patients, anti-MDA5 antibody is a useful tool for diagnosis of classic DM complicated ILD with both high sensitivity and high specificity, and is associated with poor prognosis in Chinese population
Sato S, Hirakata M, Kuwana M, Suwa A, Inada S, Mimori T, Nishikawa T, Oddis CV, Ikeda Y: Autoantibodies to a 140-kd polypeptide, CADM-140, in Japanese patients with clinically amyopathic dermatomyositis. Arthritis and rheumatism 2005, 52:1571-1576.
Bohan A, Peter JB: Polymyositis and dermatomyositis (first of two parts). N Engl J Med 1975, 292(7):344-347.
Disclosure of Interest None Declared