Clinically amyopathic dermatomyositis (CADM), a subtype of dermatomyositis with subtle or no muscle involvement, is occasionally accompanied by fatal, rapidly progressive interstitial lung disease (RP-ILD) that is resistant to aggressive immunosuppressive therapy. The presence of anti-CADM-140/MDA5 antibodies is diagnostic for patients with dermatomyositis (particularly CADM) and is known to be strongly associated with the pathogenesis, disease activity, and mortality of RP-ILD. Polymyxin-B direct hemoperfusion (PMX-DHP), originally developed for the removal of endotoxin, has been demonstrated to be effective for treating various types of acute respiratory failure. We describe a patient with amyopathic dermatomyositis who developed RP-ILD characterized by elevated anti-CADM-140/MDA5 autoantibodies, was resistant to combined steroid and immunosuppressant therapy, and was treated successfully with PMX-DHP. To our knowledge, this is the first case to indicate a serial reduction of anti-CADM-140/MDA5 autoantibodies, associated with clinical improvement, following PMX-DHP. Early intervention using PMX-DHP may improve the prognosis of RP-ILD accompanied by CADM.