We welcome the remarks by Ferri and colleagues regarding the practical application of the International rapid eye movement (REM) sleep Behavior Disorder (RBD) Study Group (IRBDSG) video-polysomnography (vPSG) guidelines for RBD diagnosis. As highlighted in their letter, the rich body of literature continuously confirming isolated RBD (iRBD) as a neurodegenerative disease in the prodromal phase is based on polysomnography (PSG)-confirmed RBD cases, underlying the "necessary objective role played by the PSG."