Maintenance of Minimal Manifestation Status with Individualized-Interval Efgartigimod in Generalized Myasthenia Gravis: Study Protocol for a Single-Arm, Open-Label Clinical Trial.

INTRODUCTION: Efgartigimod, a human immunoglobulin G1 Fc fragment targeting the neonatal Fc receptor, improves symptoms in generalized myasthenia gravis (gMG). It remains unknown whether minimal manifestation (MM) status achieved with efgartigimod can be durably maintained over the long term, and whether subcutaneous (SC) self-administration reduces treatment burden and supports quality of life. We designed a prospective study to evaluate maintenance of MM with low-dose oral prednisolone (PSL) ≤ 5 mg/day (MM-5 mg) under interval-adjusted efgartigimod administration. METHODS: This single-arm, open-label, single-center exploratory study will enroll 24 adults of either sex (aged 18 to < 80 years) with gMG who have achieved MM, defined as a Myasthenia Gravis Activities of Daily Living (MG-ADL) score ≤ 2 or MG Composite score ≤ 4, on efgartigimod with oral PSL ≤ 5 mg/day (commonly with a concomitant calcineurin inhibitor), in a preceding trial or routine care. Efgartigimod (intravenous efgartigimod alfa or SC efgartigimod alfa/vorhyaluronidase alfa) is given once weekly for 4 weeks per cycle. The intercycle interval is individualized from the worst weekly MG-ADL score: shortened by 1 week upon worsening, extended by 1 week after two stable cycles. PSL and permitted background oral immunosuppressants are held constant. Treatment lasts up to 55 weeks, with a 4-week post-observation period. PLANNED OUTCOMES: The primary endpoint is the proportion of patients maintaining MM according to prespecified cycle-level criteria throughout the observation period while receiving PSL ≤ 5 mg/day. Secondary endpoints include changes in MG-ADL, MG Composite, the revised 15-item Myasthenia Gravis Quality of Life questionnaire, Japanese version (MG-QOL15r-J), and Quantitative MG (QMG) scores; patient-reported treatment convenience; change in serum immunoglobulin G (IgG); the intercycle-interval distribution; autoantibody titers; and the time from enrollment to protocol discontinuation due to difficulty maintaining MM-5 mg. Safety is also assessed. Graphical Abstract available for this article. CLINICAL TRIAL REGISTRATION: Japan Registry of Clinical Trials (jRCT): jRCTs031260127 (prospectively registered on 14 May 2026).