Peak expiratory flow (PEF), the single-breath count test, and, to a lesser extent, the modified Medical Research Council (mMRC) dyspnea scale are all useful tools for estimating respiratory function in individuals with myasthenia gravis (MG), according to study findings published in Neurología, the official journal of the Spanish Neurology Society.
It is well known that MG is an antibody-mediated autoimmune disease in which patients exhibit fluctuating, fatigable muscle weakness that often involves the bulbar and respiratory muscles. Given the severity of respiratory issues in MG, the routine assessment of respiratory function among patients is critical.
In the current cross-sectional, correlational, observational study, researchers sought to identify useful clinical markers of respiratory involvement in MG. They evaluated the relationship between pulmonary function test parameters (forced vital capacity [FVC], maximal inspiratory pressure [MIP], maximal expiratory pressure [MEP]) and a battery of semiological tests (single-breath count test, neck strength test, mMRC, peak expiratory flow [PEF]) in patients with MG.
A total of 45 patients (35 women) with MG were included in the study based on neuromuscular diseases and neurophysiology consultations in the Neurology Department at Hospital Ramos Mejia, Buenos Aires, Argentina. The patientswere all evaluated and diagnosed with MG between 2016 and 2018. All were older than 18 years of age, with a mean age of 40.7 years (range, 18 to 82 years) at the time of evaluation. The mean age of MG onset was 32.5 years.
Overall, 89% of patients were seropositive for anti-acetylcholine receptor antibodies, 4% presented with anti-muscle-specific tyrosine kinase antibodies, and 7% were double-seronegative. At the time of assessment, based on Myasthenia Gravis Foundation of America criteria, 2 patients were classified as class I MG, 35 as class II, 7 as class III, and 1 as class IV.
Results of the study showed that positive correlations were reported between single-breath-count test scores and FVC values (r =0.57; P =.000), as well as between PEF and FVC values (r =0.76; P =.000). The severity of dyspnea, based on the mMRC scale, demonstrated a negative correlation with FVC values (r = –0.31; P =.03). Additionally, PEF exhibited a significant correlation with MEP (r =0.51; P =.002).
According to the researchers, “Determining the risk of respiratory muscle involvement in MG is fundamental in everyday practice, as this screening offers prognostic information and has therapeutic implications.”
Aguirre F, Fernández RN, Arrejoría RM, et al. Peak expiratory flow and the single-breath count test as markers of respiratory function in patients with myasthenia gravis. Neurología (Engl Ed). Published online July 14, 2022. doi:10.1016/j.nrleng.2020.09.006