Abstract Objectives This study aimed to quantify nailfold capillary (NFC) abnormalities in anti–melanoma differentiation–associated gene 5 (MDA5) -positive DM patients and to evaluate the association with clinical parameters, including serum biomarkers. In addition, we aimed to clarify the period leading to remission of NFC abnormalities during immunosuppressive treatment in patients with DM. Methods A prospective observational study was conducted including patients (n = 10) who first visited Hiroshima University Hospital and were diagnosed with DM or clinically amyopathic DM with anti-MDA5 antibodies. We compared the NFC abnormalities detected by nailfold-video capillaroscopy (NVC), physical findings, blood tests, respiratory function tests, and vascular-related growth factors measured using a LEGENDplexTM Multi-Analyte Flow Assay Kit. Results NFC abnormalities improved in all patients from 2 to 17 weeks after the initiation of immunosuppressive treatment. The NVC scores were inversely correlated with anti-MDA5 antibody titres at baseline. NVC scores and forced vital capacity were positively correlated. Baseline values of M-CSF and stem cell factor were correlated with anti-MDA-5 titres. Conclusion Our study suggested that NVC scores and disease activity were inversely correlated before treatment. Vascular-related growth factors, such as M-CSF and stem cell factor, may be associated with the disease mechanism in patients with anti-MDA5 antibody-positive DM.