Detection of serum ferritin in patients with idiopathic inflammatory myopathies and its clinical significance

Abstract

Objective To determine serum ferritin levels in patients with idiopathic inflammatory myopathies(IIM), including dermatomyositis(DM), clinical amyopathic dermatomyositis(CADM)and polymyositis(PM), and to evaluate their association with disease activity, especially with interstitial lung disease(ILD). Methods Clinical data and laboratory results were collected from 120 patients with IIM. A double-site enzyme immunoassay was conducted to measure serum ferritin levels in 120 patients with IIM and 63 healthy human controls. Statistical analysis was carried out to assess the relationship of serum ferritin levels with inflammatory biomarkers, autoantibodies, serum muscle enzymes, and severity of ILD in patients with IIM. Results Serum ferritin levels were elevated in 36 out of the 120 patients, but normal in the other 84 patients. Compared with patients with normal serum ferritin levels, those with elevated serum ferritin levels showed increased levels of C-reactive protein(14.1 ± 6.5 vs. 3.6 ± 1.7 mg/L, P < 0.01), aspartate aminotransferase(111.8 ± 44.6 vs. 46.0 ± 9.0 U/L, P< 0.01), lactate dehydrogenase(388.6 ± 81.5 vs. 260.7 ± 29.1 U/L, P< 0.01), as well as erythrocyte sedimentation rate(34.8 ± 8.2 vs. 15.4 ± 2.7 mm/h, P< 0.01). However, no significant difference was observed in the level of creatine kinase between patients with elevated and normal serum ferritin levels. Moreover, serum ferritin levels were significantly higher in both IIM patients complicated with acute/subacute interstitial pneumonia(A/SIP, 650.5 ± 268.5 ng/ml)and those with chronic interstitial pneumonia(CIP, 489.9 ± 157.3 ng/ml)than in those without ILD(155.7 ± 90.8 ng/ml)and those with imageological changes but no clinical symptoms of ILD(193.3 ± 62.1 ng/ml)(all P < 0.01). Moreover, compared with patients with normal serum ferritin levels, those with elevated serum ferritin levels showed a significant increase in the incidence of CIP(52.8% vs. 25.9%, P < 0.01), A/SIP(22.2% vs. 3.5%, P < 0.01), as well as appearance of ground-glass opacity(67.6% vs. 43.4%, P < 0.05)and honeycomb-like changes(14.7% vs. 2.6%, P < 0.05)on high-resolution CT scans. Conclusion Serum ferritin levels are highly correlated with erythrocyte sedimentation rate, C-reactive protein, aspartate aminotransferase, lactate dehydrogenase, ILD and high-resolution CT findings, and may be of great clinical significance for the evaluation of disease activity, especially the severity of ILD. Key words: Myositis; Dermatomyositis; Ferritins; Lung diseases, interstitial; Idiopathic interstitial pneumonias