To compare different definitions of refractory Myasthenia Gravis (MG).

Refractory status in MG remains difficult to determine, and there are different definitions. Previous studies reported a variable prevalence of refractory MG, ranging between 10-20%. Lenient definitions can result in the unnecessary escalation of MG treatment, increasing both risks and costs for patients. In addition, disease severity and quality of life (QoL) measures are often excluded from these definitions.

We compared 5 different definitions of refractory MG: International Consensus Guideline (ICG), REGAIN study criteria, and definitions by Drachman, Mantegazza, and Suh. We reviewed 237 patient charts and applied each set of criteria at cohort inception and at last visit. We compared the proportion of refractory patients between each criteria set, as well as disease severity, fatigue, and quality of life (QoL) scores across groups.

The ICG and REGAIN refractory definitions were more conservative, resulting in 9.7% and 2.8% of refractory patients, respectively. The more lenient criteria resulted in a higher proportion of patients classified as refractory (Drachman: 40.1%; Mantegazza: 39.2%; Suh: 38.8%). Patients classified as refractory with the ICG and REGAIN criteria, had worse disease severity, fatigue, and QoL scores compared to refractory patients by other definitions.

Our study shows that the proportion of refractory MG patients depends on the definition. The more conservative criteria resulted in less than 10% of refractory patients in this cohort. The fact that patients classified as refractory with more lenient criteria had less disease severity and fatigue, and better QoL than conservative criteria, suggests that lenient definitions may unnecessarily subject patients to aggressive therapies.