Сharacteristics of respiratory dysfunction in patients with myasthenia gravis based on a comprehensive functional study

Myasthenia gravis (MG) is an autoimmune disease in which respiratory muscle weakness is manifesting itself as a life-threatening condition. However, data on comprehensive assessment of respiratory function using modern methods are rare.

The aim: to study the prevalence and nature of respiratory dysfunction in patients with MG.

Material and methods. A cross-sectional study included 66 patients (21 male and 45 females) with MG. The mean age of the participants was 57.0 ± 17.9 years, and the median disease duration was 8 [4; 12] years. Patients underwent a 6-minute walk test (SMWT), mMRC dyspnea estimation, spirometry, body plethysmography, pulse oscillometry, measurement of maximal inspiratory and expiratory pressures (MIP, MEP), and diffusing capacity of lungs (DLCO).

Results. The most common disorder was a decrease in respiratory muscle strength: MIP < 80% in 65.6%, MEP < 80% – 50.8% in the studied patients with MG. Restrictive disorders according to spirometry data (forced vital capacity < 80%) were detected in 22.7%, according to body plethysmography data (total lung capacity < 80%) – in 17.7% of patients, obstructive disorders (the ratio of forced expiratory volume in 1 second to forced vital capacity < 70%) – in 18.2% of participants. Hyperinflation (the ratio of residual volume to total lung capacity >40%) was noted in 24.2%, a decrease in inspiratory capacity < 80% – in 41.9% of patients. Among patients, in whom with pulmonary diffusion capacity assessment was performed (n = 7), decreased DLCO and alveolar volume were observed in 85% of cases, and decreased KCO (the ratio of DLCO to alveolar volume) in 28.6%. According to pulse oscillometry data (n = 24), increased respiratory resistance at 5 Hz (R5 >120%) was recorded in 50% of patients, and an increase in resonance frequency (Fres >100%) was observed in 58.3% of participants. Decreased exercise tolerance (SMWT < 500 m) was observed in 42.4%, clinically significant dyspnea (mMRC ≥2) in 25.7%, significant symptoms according to MG-ADL (≥6 points) in 34.8% of patients.

Conclusion. The study results demonstrate a high frequency of functional disorders in patients with myasthenia gravis. Obtained data substantiate the need to integrate pulmonary screening into the standard care of patients with neuromuscular disorders.