The pathogenesis of immune-mediated necrotizing myopathy: Progress and therapeutic implications.

Immune-mediated necrotizing myopathy (IMNM) is an emerging and severe form of myositis. Most patients experience persistent muscle weakness or recurrent attacks within their lifetime. The previous view suggests that autoimmune and complement activation play a key role in muscle damage, and aggressive immunotherapy may benefit patients. However, many patients respond poorly to conventional glucocorticoid and immunosuppressant therapy. Emerging evidence further confirmed the role of anti-signal recognition particle (SRP) and anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies in disease development. Autoantibodies may cause muscle damage by internalizing and inhibiting the function of SRP/HMGCR proteins, disturbing protein and lipid metabolism, rather than through a complement-dependent mechanism. Muscle inflammation and activation of the ER stress-autophagy have a dual effect on muscle damage and repair. Moderate activation of these processes helps restore myofiber homeostasis, clear myonecrosis, and regulate regeneration, while excessive activation exacerbates muscle damage. Novel therapies that suppress pathogenic antibody production or accelerate their clearance-such as B-cell depletion therapy, chimeric antigen receptor (CAR) T-cell therapy, BAFF/APRIL inhibitors, and efgartigimod-present great therapeutic potential. A better understanding of IMNM pathogenesis may help clinicians design targeted treatment strategies.