Eculizumab

Complement Inhibition: Complement-mediated microvascular injury is a hallmark of dermatomyositis pathology – deposition of the membrane attack complex (C5b-9) in muscle capillaries leads to ischemic muscle fiber damage. This has prompted interest in inhibitors of the complement cascade.

Eculizumab, a monoclonal antibody against C5, is the prototypical agent. In two severe refractory dermatomyositis cases reported by French clinicians, adding eculizumab to ongoing immunosuppressive therapy achieved complete and rapid remission . Both young female patients had DM with systemic involvement that failed conventional treatments; eculizumab led to remission and notably, neither patient relapsed during follow-up of 18 months and 4 years (while continuing maintenance therapy) . These anecdotal successes suggest complement blockade can shut down the vascular injury driving DM.

Another report described* two anti-NXP2 *antibody-positive dermatomyositis patients with severe gastrointestinal vasculitis and perforations – a life-threatening complication – who were rescued with eculizumab, achieving healing of GI ulcers .

While no large trials have yet been published (a planned Phase II in DM was initiated but results are not fully published ), these cases are compelling. It is notable that eculizumab is already approved for refractory anti-AChR myasthenia gravis, another complement-mediated muscle disease. Thus, targeted complement inhibition may become a valuable tool for DM and possibly for immune-mediated necrotizing myopathies (IMNM) like anti-SRP or anti-HMGCR myopathy, where complement deposits on muscle fibers are also observed. Future studies may explore C5 inhibitors (like eculizumab or newer long-acting agents), C5a receptor blockers, or C1q inhibitors in these contexts. In summary, neutralizing the complement cascade addresses a root cause of muscle fiber destruction in complement-driven IIM subtypes, with early evidence of efficacy in desperate cases .