In Myasthenia gravis, FcRn antagonism reduces pathogenic IgG levels by blocking the neonatal Fc receptor (FcRn), which is responsible for protecting IgG from lysosomal degradation. When FcRn is inhibited, IgG—including pathogenic anti-AChR antibodies—is no longer recycled back into circulation and is instead broken down more rapidly, leading to a rapid decline in circulating autoantibody levels. This mechanism is distinct from broad immunosuppression because it selectively accelerates antibody clearance rather than suppressing overall immune cell function.

MG-ADL (Myasthenia Gravis Activities of Daily Living) scores are commonly used to quantify symptom severity and functional impairment in daily activities such as swallowing, speech, breathing, and limb strength. A meaningful treatment response is typically reflected by a reduction in MG-ADL score, often by ≥2 points or more, alongside improvements in specific patient-reported symptoms. Serial MG-ADL assessments are particularly useful for tracking response to therapies like FcRn inhibitors, where clinical improvement may be relatively rapid compared with traditional immunosuppressants.

When counseling a patient like this, it is important to emphasize that FcRn-targeted therapy can be used as part of a broader, individualized long-term management plan rather than as a replacement for all immunosuppression. Traditional agents such as azathioprine may still play a role in maintaining disease control, but the goal may be to reduce reliance on corticosteroids and minimize cumulative steroid exposure. Shared decision-making should focus on balancing rapid symptom control, long-term disease stability, and minimizing treatment-related adverse effects while regularly reassessing functional outcomes and respiratory risk.

FcRn antagonism works by blocking the neonatal Fc receptor that normally salvages IgG antibodies from lysosomal degradation and recycles them back into circulation. By occupying this receptor, FcRn-targeted therapy accelerates the clearance of all circulating IgG, including the pathogenic AChR antibodies driving neuromuscular junction dysfunction in Ms. L. What makes this mechanism particularly valuable in refractory AChR-positive gMG is that it operates entirely independently of the upstream immunosuppressive pathway, meaning it can reduce antibody burden rapidly without requiring escalation of steroids or intensification of conventional immunosuppression.

MG-ADL scoring is most informative when tracked longitudinally rather than interpreted as a single snapshot. For Ms. L, with a baseline score of 11 reflecting significant functional impairment across bulbar, ocular, and limb domains, I would establish a clear response benchmark early and monitor serially at consistent intervals. A reduction of 2 or more points is generally considered clinically meaningful, but I pay particular attention to which specific domains are improving, since persistent dysphagia or fatigable ptosis despite overall score reduction may signal incomplete response or the need for dosing adjustment.

Counseling Ms. L requires directly addressing her steroid avoidance concern, which is clinically legitimate given her diabetes and hypertension. I would frame FcRn-targeted therapy not as a replacement for background immunosuppression but as a steroid-sparing strategy that allows us to maintain azathioprine while achieving more rapid and meaningful disease control without escalating corticosteroid burden. The goal over time would be optimizing her background immunosuppression based on clinical stability, antibody trajectory, and functional outcomes, while using MG-ADL and MG-QOL15r scores together to capture both the functional and patient-reported dimensions of her response.

1: FcRn (neonatal Fc receptor) antagonists reduce pathogenic IgG autoantibodies by disrupting the body's natural IgG recycling system, ultimately accelerating the destruction of these disease-causing proteins
2: helps to quantify response
3: would recc trying to avoid steroids if possible