MG Treatments Should Consider Patients’ Elevated Risk Of Serious Infections, Study Suggests

People with myasthenia gravis (MG) are at higher risk of developing serious infections than those without the condition, a recent study has found.

Although more research into the causes is needed, this finding may have implications for prevention strategies such as vaccinations and preventive antibiotic use, the researchers said.

The study, titled “Serious Infections in Patients with Myasthenia Gravis: population‐based cohort study,” was published in the European Journal of Neurology.

MG is an autoimmune disease that is caused by the immune system attacking the body’s own cells. As such, most treatment strategies aim to suppress the activity of the immune system.

These treatments and the immune dysregulation of MG could, in theory, increase the risk of infections for people with the condition, as the immune system is normally responsible for fighting off infectious agents. Such elevated risk has been shown in other autoimmune disorders, such as rheumatoid arthritis.

Some aspects of MG, such as reduced mobility and weakness in respiratory muscles, may increase the risk of infection as well.

In the study, researchers analyzed data collected through the public health insurance program in Ontario, Canada. Using insurance codes, they identified 3,823 people with MG and 15,292 people without MG. The two groups were matched in terms of age (average 63.8 years), sex (47% female), and location of residence.

The rates of serious infections, identified using insurance codes, were compared between the two groups. For this study, a serious infection was defined as one requiring hospitalization or a visit to the emergency department.

With an average follow-up time of 5.4 years, 33.4% of people with MG (1,275 patients) experienced a serious infection, compared to 19.4% of those without the condition (2,973 participants). This corresponds to rates of 72.5 infections per 1,000 person-years for those with MG, and 35.0 infections per 1,000 person-years for those without the condition.

A subsequent statistical analysis, which took into account baseline differences between the groups, found a 39% higher risk of infection among those with MG.

The most common infections among people with MG were respiratory (22%), with bacterial pneumonia accounting for 16% of all infections.

Additionally, infections with Varicella zoster (VZV), the virus that causes chickenpox and shingles, were significantly more common among people with MG (2.2% vs. 0.9% for those without MG).

These findings are of particular interest because prevention strategies are available and could be employed. Prophylactic antibiotic use, for instance, could help to limit bacterial pneumonia.

Furthermore, vaccines against VZV are available, including a relatively newer version that is effective at preventing the more serious shingles in adults.

“The newer inactivated VZV vaccine is both highly effective and safe for immunosuppressed patients,” the researchers wrote. “We suggest that the risk for VZV should be discussed with MG patients (especially those on immunotherapy) and the inactivated vaccination offered.”

Although the findings suggest an overall higher risk of serious infections in people with MG, this study is not without limitations.

First, data based on insurance claims is not a perfect representation of clinical data. For instance, a higher rate of flu was found in people with MG, but this only includes people who had a related insurance claim. As such, anyone who had the flu, but did not seek hospitalization or other substantial treatment, would not have been included.

This is particularly noteworthy because, “MG patients may be more likely to seek medical attention for concerning symptoms given their existent disease status,” the researchers wrote, so the relative difference in infection rates may be over-estimated in this study.

However, “most guidelines recommend in favor of influenza vaccination in MG patients, particularly those patients with co-existent cardiac or respiratory illnesses,” the researchers noted.

Another limitation of the study is that MG severity and treatments were not assessed due to a lack of available data. Therefore, whether the increased risk of infection is a result of these treatments or of the condition itself is unclear.

“We believe these data will be helpful to clinicians in counselling MG patients regarding infection risk, highlighting the importance of vigilance to monitor for certain infection types, and in deciding whether or not to use prophylactic antibiotics,” the researchers said.

“Determining whether this risk is due to the use of immunosuppressive medications versus MG itself is an important area for future research,” they added.