Simple Blood Test May Help Predict Respiratory Failure in MG Patients

Examination of biomarkers revealed platelet-to-lymphocyte ratio as key indicator

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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The platelet-to-lymphocyte ratio (PLR), which can be readily measured from a simple blood test, may help tell which people with myasthenia gravis (MG) will go on to develop respiratory failure, a study has found.

High levels of systemic (whole-body) inflammatory markers or a diagnosis of generalized MG were also identified as risk factors for worse clinical outcomes.

The study, “The systemic inflammation markers as possible indices for predicting respiratory failure and outcome in patients with myasthenia gravis,” was published in the Annals of Clinical and Translational Neurology.

MG occurs when self-reactive antibodies misguidedly disrupt the normal communication between nerve cells and muscle cells. As a result, muscles begin to weaken and waste away.

Treatment may help ease MG symptoms by getting inflammation under control, “but the therapeutic response often varies,” a team of researchers in China wrote.

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Measuring biomarkers for response to treatment, disease progression

To keep track of systemic inflammation, researchers measured a number of biomarkers to find out which could be used to see how well the body responds to treatment or how the disease is progressing.

“Easily available biomarkers have been reported as highly sensitive measures of inflammation in several autoimmune diseases,” they wrote.

They focused on four of these biomarkers, all of which can be measured from a simple blood test: the neutrophil-to-lymphocyte ratio (NLR), PLR, lymphocyte-to-monocyte ratio (LMR), and systemic immune-inflammation index (SII).

The study included 117 people who were diagnosed with MG at a single Chinese hospital; 58 (49.6%) had ocular MG and 59 (50.4%) had generalized MG, a more severe form of the disease. Their median age was 58 years.

About one-quarter (26.5%) of the patients experienced their first symptoms before the age of 50, whereas the remaining 73.5% had their first symptoms when they were 50 or older.

As controls, the study included 120 healthy individuals who had visited the hospital for a physical examination. Their median age was 54 years.

White blood cell counts were significantly higher in patients than in controls, as were the number of neutrophils, a type of white blood cells, and platelets. Conversely, the number of lymphocytes, another type of white blood cells, was significantly lower in patients than in controls.

As a result, NLR, which is the number of neutrophils divided by that of lymphocytes, and PLR, which is the number of platelets divided by the number lymphocytes, were significantly higher in patients than in controls.

The same was true for SII, which is calculated by multiplying the number of platelets by that of neutrophils, and then dividing the total by the number of lymphocytes.

These three biomarkers correlated positively with the Myasthenia Gravis Foundation of America (MGFA) classification, a measure of disease severity. In other words, the higher the biomarkers, the more severe the MG.

When muscles involved in breathing become weak, patients may have difficulty breathing and even develop respiratory failure, which occurs when the lungs fail to transfer enough oxygen into the bloodstream. At admission to the hospital or during hospitalization, 21 (17.9%) patients developed respiratory failure.

Of all four biomarkers, PLR was identified as an independent predictor of respiratory failure in people with MG. PLR worked well to distinguish patients who went on to develop respiratory failure from those who did not, with a sensitivity of 71.4% and a specificity of 88.5%. Sensitivity is the ability a given test or parameter has of correctly identifying those with a condition, while specificity is its ability of correctly identifying those without it.

A total of 90 patients were followed up by phone or chat every month, and every one to three months in person. Of these, 64 (71.1%) went on to have good outcomes, whereas the remaining 26 (28.9%) had poor outcomes. A high SII or a diagnosis of generalized MG were risk factors for poor clinical outcomes.

“These systemic inflammation markers [are] easily measurable, available, and cost-effective parameters,” the researchers wrote, adding that larger studies are needed to confirm the clinical relevance of these biomarkers.