An Extension Study for Participants Who Have Completed the Treatment Period of a Qualifying Parent Study

Inclusion Criteria: * Participants aged ≥18 and ≤80 with moderate to severe dermatomyositis (DM), that have completed the treatment period of a qualifying study. * Capable of giving signed informed consent. * Participants who are willing and able to comply with all scheduled visits, treatment plan, laboratory tests, lifestyle considerations, and other study procedures. Exclusion Criteria: * Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study * Participants who met discontinuation criteria at any point during the participating qualifying studies. * Participants with an ongoing safety event in the qualifying studies which, in the opinion of the investigator or sponsor, is an ongoing safety concern OR the participant has met safety monitoring criteria in the qualifying study that has not resolved.