Peak expiratory flow (PEF), a single-breath counting test, and the modified Medical Research Council dyspnea scale (mMRC) are useful measurements of respiratory involvement in patients with myasthenia gravis (MG), according to a study published in Neurología.

The researchers found these measurements correlated with forced vital capacity (FVC), maximal inspiratory pressure (MIP), and maximal expiratory pressure (MEP).

“Simple, accessible maneuvers enabling neurologists to estimate the degree of respiratory impairment in MG would be a valuable tool,” the authors wrote.

“This study aimed to evaluate the correlation between pulmonary function test parameters (FVC, MIP, and MEP) and a battery of selected semiological tests (single-breath count test, neck strength test, [mMRC], [PEF]) in patients with MG.”

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The research team conducted a cross-sectional correlational study of 45 adult patients diagnosed with MG at a single center in Buenos Aires, Brazil. All patients underwent the single-breath count test, PEF determination, spirometry, and FVC, MIP, and MEP pulmonary function tests. The patients’ self-reported measures related to the mMRC scale.

The results showed a negative correlation between mMRC results and FVC, suggesting that mMRC could be a useful clinical tool in practice, along with the PEF and single-breath count tests, which correlated with the results of spirometry and predicted over half of the FVC variance in the studied patients.

The team concluded that the PEF and the single-breath test were particularly useful for determining the current respiratory function in patients with MG, and to a lesser extent, the mMRC dyspnea scale was also correlated with respiratory involvement in these patients. Given the simplicity and availability of these tools, the authors recommend employing these instruments routinely to provide useful prognostic information and implications for treatment.


Aguirre F, Fernández RN, Arrejoría RM, et al. Peak expiratory flow and the single-breath counting test as markers of respiratory function in patients with myasthenia gravis. Neurología. Published online July 14, 2022. doi:10.1016/j.nrleng.2020.09.006