Gender, Race, and Thymectomy Increase Risk for Lupus in MG

Vanda Pinto, PhD avatar

by Vanda Pinto, PhD |

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People with myasthenia gravis (MG) have an increased risk of developing systemic lupus erythematosus or SLE, another type of autoimmune disorder, according to recent study findings that suggest “a real association between these two diseases.”

Especially at risk are African American women, those who had surgery to remove the thymus, and MG patients with other immune system disorders.

“Our study strongly supports the higher prevalence of SLE in MG patients and highlights the risk factors of the development of lupus in MG patients,” the researchers wrote. “MG patients should be evaluated for the coexistence of SLE especially in post-thymectomy patients and the young African American women with a history of other autoimmune diseases.”

These findings were presented at the American College of Rheumatology (ACR) Convergence 2021, recently held virtually, in a poster titled “Association Between Systemic Lupus Erythematosus and Myasthenia Gravis: A Population-Based National Study.”

MG and SLE are two autoimmune conditions that affect mostly young women. Both are characterized by periods of disease-related symptoms that worsen over time, followed by times when symptoms are less severe.

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In SLE, the most common type of lupus, the symptoms depend on what part of the body is affected — which may include the joints, skin, kidneys, and brain. Lupus causes widespread inflammation and leads to tissue damage in the affected organs.

The presence of antinuclear antibodies in the blood, a marker of autoimmune disease, is a feature of both MG and SLE.

Coexisting cases of SLE and MG have been previously reported and, in most of these, patients were first diagnosed with MG. However, whether these two diseases are, in reality, linked is unknown.

To address this knowledge gap, a team of U.S. researchers — from Boston University, OhioHealth Hospital, the MetroHealth System Campus of Case Western Reserve University, in Ohio, and the Oklahoma Medical Research Foundation — conducted an observational study. Their goals were to determine the frequency of SLE among MG patients and to pinpoint the differences between people with MG who developed SLE before or after receiving an MG diagnosis.

The researchers examined medical records of patients included in the IBM Explorys database, an online platform that contains anonymized data from more than 60 million patients in the U.S.

In their analyses, the team included adults with SLE and MG, as well as control patients. Several parameters were examined, including age, race, gender, smoking status, thymectomy (thymus removal surgery), and the co-existence of other health conditions.

Among a total of 59,896,040 patients, 65,000 (0.1%) had SLE and 26,110 (0.04%) had MG — rates similar to those previously reported. SLE was found to be more common among MG patients than in control individuals (1.42% vs. 0.11%). In fact, people with MG had a 13.38 times higher probability of developing SLE compared with controls.

Patients with both conditions were then compared with those who only had MG — and several risk factors were identified.

Most people who developed both conditions were women (89.19% vs. 54.53%), of African American descent (18.92% vs. 10.76%), who had undergone total (8.11% vs. 2.64%) or partial (5.4% vs. 1.89%) thymectomy.

Statistical analysis also revealed that MG patients who had previously undergone a thymectomy had a threefold higher risk of developing SLE.

“Female sex, African American race, thymectomy, autoimmune diseases, and miscellaneous comorbidities [co-existing medical conditions] such as thyroid disease were significantly more common in MG patients who developed lupus,” the researchers concluded.