Cardiopulmonary exercise testing in mild generalized myasthenia gravis: an exploratory pilot feasibility study

We conducted an exploratory pilot feasibility study to assess the safety and feasibility of cardiopulmonary exercise testing (CPET) in patients with mild generalized myasthenia gravis (gMG), aiming to determine whether test termination results from systemic exertion or MG-specific neuromuscular fatigability and to evaluate short-term effects on fatigue.

Nine patients with mild gMG (median age of 58 years, IQR 46.0-66.5) were included in this exploratory feasibility study and underwent a single maximal incremental CPET on a cycle ergometer with breath-by-breath gas exchange analysis and blood lactate measurements. Predefined exertion criteria (EC) included respiratory exchange rate (RER; ≥1.1), ventilatory equivalent for O₂ (EQO₂; ≥30), attainment of age-related maximum heart rate (ARMHR), peak blood lactate concentration (>6 mmol·L^-1), and Borg Scale for Rated Perceived Exertion (RPE; ≥17). Repetitive nerve stimulation (RNS) was performed before and after CPET to assess neuromuscular fatigability. Fatigue was assessed using the Chalder Fatigue Scale (CFS) at baseline and 4 weeks after CPET.

CPET was completed by all participants without adverse events. All reported symptoms resolved within 30 min after exercise termination, and no participant required medical intervention. All participants completed the maximal incremental CPET according to the predefined protocol. Among the predefined EC, 44% of participants achieved an RER ≥1.1, 78% an EQO₂ ≥30, 44% an ARMHR, 67% reached a peak blood lactate concentration >6 mmol·L^-1-, and 67% an RPE ≥17. A decremental response in RNS was observed in 78% both before and after CPET. No relevant changes in CFS scores were detected over 4 weeks.

CPET appears safe and feasible in mild gMG, with exercise termination primarily driven by systemic exertion rather than MG-specific neuromuscular fatigue. CPET may complement clinical evaluation by supporting individualized training recommendations and the identification of cardiopulmonary limitations.