Functional Status Enhances the FRAX^® Prediction of Fractures in Myasthenia Gravis: A 10-Year Cohort Study

Background: Patients with myasthenia gravis (MG) are susceptible to fractures due to glucocorticoid (GC) use and disease-related functional impairment affecting activities of daily living (ADL). The Fracture Risk Assessment Tool (FRAX^®) estimates fracture probability but does not incorporate disease-specific functional status. We investigated whether combining FRAX^® with the Myasthenia Gravis Activities of Daily Living (MG-ADL) scale improves fracture risk stratification in MG patients. Methods: This single-center prospective cohort study followed 53 MG patients for 10 years (2012-2022) at Toho University Ohashi Medical Center, Japan. Patients were categorized into four groups based on baseline FRAX^® probability (calculated with bone mineral density [BMD]) and MG-ADL scores using median splits: high FRAX^®/high MG-ADL (HH), high FRAX^®/low MG-ADL (HL), low FRAX^®/high MG-ADL (LH), and low FRAX^®/low MG-ADL (LL). The primary outcome was incident major osteoporotic fracture (MOF). Results: Over 10 years, nine MOFs occurred: seven in the HH group (43.8%), two in the HL group (16.7%), and none in the LH or LL groups. Fracture-free survival differed significantly among the groups (log-rank p < 0.001), with the HH group exhibiting the lowest survival rate. Baseline characteristics, including age, disease duration, MG severity scores, BMD, and FRAX^® scores, differed significantly among groups. Specific MG-ADL items reflecting greater impairment (impairment of ability to arise from a chair, double vision, and ptosis) were significantly more pronounced in the HH group at baseline. Conclusions: Combining baseline FRAX^® scores with the MG-ADL assessment effectively stratifies long-term MOF risk in patients with MG. Individuals with both high FRAX^® and high MG-ADL represent a particularly high-risk subgroup. This dual-assessment approach may improve the identification of patients requiring targeted preventive interventions.