Phase 3 Trial of Pamrevlumab or Placebo With Systemic Corticosteroids in Participants With Non-ambulatory Duchenne Muscular Dystrophy (DMD)

This is a global, Phase 3, randomized, double-blind trial of pamrevlumab or placebo in combination with systemic corticosteroids in participants with non-ambulatory Duchenne muscular dystrophy, aged 12 years and older. Approximately 90 male participants will be randomized at a 1:1 ratio to Arm A (pamrevlumab + systemic corticosteroid) or Arm B (placebo+ systemic corticosteroid), respectively. Participants must be fully informed of the potential benefits of approved products and make an informed decision that they prefer to participate in a clinical trial in which they could be randomized to placebo. This trial has 3 study periods: * Screening period: Up to 4 weeks * Treatment period: 52 weeks * Safety Follow-up period/End of Study (EOS): A visit 28 days (+/- 3 Days) and a final safety follow-up phone call 60 days (+ 3 Days) after the last dose In the screening period, participants will be evaluated per the protocol inclusion/exclusion criteria to determine eligibility for participation in this trial. During the treatment period, each participant will receive pamrevlumab or placebo at 35 mg/kg every 2 weeks for up to 52 weeks. Participants who complete the 52-week study (either arm) may be eligible for rollover into an open-label extension treatment (OLE) with pamrevlumab + systemic corticosteroids. Participants who discontinue study treatment for any reason should be encouraged to return to the investigative site to complete final safety and efficacy assessments.