Using the serum LDH level as a biomarker for amyopathic dermatomyositis with interstitial lung disease: A retrospective study of 158 patients with nonspecific interstitial pneumonia or organizing pneumonia

Background: Lactate dehydrogenase (LDH) is an easily obtained biological marker and a promising index for determining the severity of amyopathic dermatomyositis with interstitial lung disease (ADM-ILD). In this study, we retrospectively analysed the clinical signs and laboratory data from ADM-ILD patients displaying nonspecific interstitial pneumonia (NSIP) or organizing pneumonia (OP) ILD radiological patterns, and we identified the serum LDH level as a useful biomarker for early ADM-ILD detection. Methods: In our cohort study, 158 Chinese patients were divided into four groups according to whether NSIP or OP patterns were present on high-resolution computed tomography (HRCT). The 4 groups included 25 ADM-NSIP and 92 control-NSIP patients, 15 ADM-OP patients, and 29 control-OP patients. Patient’s demographic features, clinical presentation, laboratory parameters, duration of ILD, and follow-up data were recorded and analysed. Results: ADM-ILD patients generally had higher AST (45.96 ± 42.45 in NSIP, 64.53 ± 75.75 in OP, U/L) and LDH (317.20 ± 104.29 in NSIP, 356.60 ± 214.84 in OP, U/L) levels than the corresponding control groups. A total of 40.53% (15/37) and 86.49% (32/37) of ADM-ILD patients had high serum levels of AST and LDH above the normal range, respectively. At a cut-off level of 235.5 U/L, identified by the ROC curve, serum LDH yielded a sensitivity of 78.38% and specificity of 82.64% for ADM with NSIP or OP radiological patterns. The 5-year overall survival rate of ADM-OP patients (73.33%) was significantly worse than that of control-OP patients (94.12%) ( p =0.007). No difference was evident in the survival rate between the NSIP groups. The presence of skin ulcers ( p =0.028) and OI<300 mmHg ( p =0.029) were significant risk factors for poor outcomes in ADM-ILD patients. A lower serum level of ferritin (< 500 ng/ml) indicated a better patient prognosis ( p =0.023). The presence of coexistent myositis-associated autoantibodies with anti-melanoma differentiation-associated gene 5 (anti-MDA5) seems to protect ADM-ILD patients. Conclusions: The LDH level can be used as a screening biomarker for patients with NSIP or OP ILD radiological patterns. It is important to recognize ADM-ILD early, especially in patients with the OP radiological pattern, which appears to impact patient treatment and outcomes.