Anti-melanoma differentiation-associated gene 5 (MDA5) antibody-positive clinically amyopathic dermatomyositis (CADM) is a subtype of dermatomyositis without severe myositis but with characteristic cutaneous manifestations and severe interstitial lung disease. Joint symptoms can occur in patients with anti-MDA5 antibody-positive CADM. However, the treatment strategy and utility of ultrasound for treating joint symptoms remain unknown. We herein report an 85-year-old man with anti-MDA5 antibody-positive CADM who presented with ultrasound-confirmed synovitis that improved with medium-dose corticosteroid therapy.