MG patients 2 times as likely to have other autoimmune diseases

People with myasthenia gravis (MG) are twice as likely to be diagnosed with other autoimmune diseases, both before and after an MG diagnosis, than a matched general population, a new study involving patients from Denmark found.

This predisposition was particularly strong among patients younger than 50 — meaning those with early-onset MG, known as EOMG — and women, the data show.

According to the researchers, these findings indicate a greater risk, among people with MG, of what’s known as polyautoimmunity, defined as the presence of more than one autoimmune disease in a single patient. The team theorized that an underlying disease-causing mechanism may be at work.

“The higher risks of having another [autoimmune disease] preceding or succeeding MG diagnosis suggest a common [disease-causing] mechanism predisposing to poly-autoimmunity, particularly in young, female patients,” the scientists wrote.

The study, “Associated Autoimmunity in Myasthenia Gravis in Denmark: A Nationwide Case–Control Study,” was published in the European Journal of Neurology.

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MG is an autoimmune disease characterized by symptoms that include weakness and fatigue affecting muscles involved in voluntary movements. In most cases, it is caused by self-reactive antibodies that target proteins involved in nerve-muscle communication, usually acetylcholine receptors (AChRs).

Investigating if other autoimmune disease come before or after MG

The disease is frequently associated with other autoimmune diseases, such as lupus and rheumatoid arthritis. It’s often unclear, however, whether these conditions precede or follow an MG diagnosis.

To learn more, a research team from Aarhus University Hospital analyzed 1985-2020 data from the Danish National Patient Registry. Their goal was to gain a better understanding of the frequency and temporal relationship between MG and other autoimmune diseases.

Overall, the data covered 2,110 adults with MG and 21,100 age- and sex-matched controls from the general population. The controls also were matched by diagnostic date to the patients. Both groups were fairly evenly divided by sex.

Nearly three-quarters of the MG patients were diagnosed after age 50. Patients were more likely to have had coexisting conditions than their matched controls (32.8% vs. 25.9%).

During the study period, 110 MG patients (5.2%) and 580 matched controls (2.7%) were diagnosed with at least one autoimmune disease before the MG diagnosis or the matched diagnostic date. This corresponded to a nearly twice the risk in MG patients.

The higher risk associated with MG was even more pronounced among people age 50 or younger, by threefold. Women and people without coexisting conditions also were seen to be at higher risk, by slightly more than two times.

Similar results were obtained when statistical analyses were adjusted for a thymus gland tumor, which is present in as many as 10%-15% of individuals with MG and is thought to contribute to the disease.

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Nearly 4 times risk seen for people with early-onset MG

Most other autoimmune diseases were diagnosed within five years before the MG diagnosis. People with MG were twice as likely to already have another autoimmune disease — diagnosed five years before the MG diagnosis — than those without the condition.

The most frequently diagnosed autoimmune diseases before MG onset were autoimmune thyroiditis, or inflammation of the thyroid gland, systemic lupus erythematosus, which is the most common form of lupus, and pernicious anemia. Pernicious anemia reduces the body’s capacity to absorb vitamin B12, resulting in low levels of the vitamin and fewer red blood cells carrying oxygen throughout the body (anemia).

Similar patterns were seen for autoimmune diseases diagnosed after MG. A total of 110 MG patients (5.2%) and 573 controls (2.7%) were subsequently diagnosed with an autoimmune disease, reflecting a twofold higher risk associated with MG.

People with EOMG had a nearly fourfold higher risk of developing other autoimmune diseases compared with their matched controls, the data showed. Women with MG and MG patients without other coexisting conditions had each an increased risk of a co-occurring autoimmune disease diagnosis, by about 2.5 times, relative to controls.

The findings underscore the importance of clinical awareness. … A deeper understanding of the spectrum of [autoimmune diseases] associated with MG could enhance diagnostic accuracy and improve treatment strategies.

“This aligns with the well-known genetic predisposition in EOMG, where [a specific cluster of genetic variants] is linked to multiple autoimmune diseases … and may explain the age-related patterns,” the researchers wrote.

The most strongly associated autoimmune diseases with an established MG diagnosis were the same as those identified before an MG diagnosis, with the addition of immune thrombocytopenic purpura, a bleeding disorder, and type 1 diabetes.

“This nationwide population-based study from 1985 to 2020 found that MG patients are twice as likely to be diagnosed with [autoimmune disease] before as well as after MG diagnosis, with particularly elevated risk in females and younger patients,” the team wrote, noting that “the observed patterns align with prior research.”

“The findings underscore the importance of clinical awareness,” the researchers concluded. “A deeper understanding of the spectrum of [autoimmune diseases] associated with MG could enhance diagnostic accuracy and improve treatment strategies.”