Myasthenia gravis plus thymectomy increases risk for lupus
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Patients with myasthenia gravis — particularly those post-thymectomy — demonstrate an increased odds for having systemic lupus erythematosus, according to a speaker at the 2021 North American Young Rheumatology Investigator Forum.
“Many case series and retrospective studies have shown a high association between myasthenia gravis and lupus, with the majority of cases having myasthenia gravis preceding lupus,” Sali Merjanah, MD, of Boston University Medical Center, told attendees at the forum. “There is an increased risk of associated autoimmune diseases in general with patients who have myasthenia gravis. The most common are thyroiditis, lupus and rheumatoid arthritis, with thyroiditis being the most prevalent.”
“It is estimated that while half of lupus patients are affected by neuropsychiatric lupus, the prevalence of myasthenia gravis as a peripheral neuropsychiatric lupus is only at 0.2%,” she added. “A study of 78 patients with myasthenia gravis showed a higher prevalence of lupus, at 7.7%. A cohort study of 1,300 lupus patients showed a high prevalence of myasthenia gravis, and they estimated the occurrence of lupus in myasthenia gravis at 8%, which greater than the general population.”
To examine the association between myasthenia gravis and SLE, Merjanah and colleagues conducted a retrospective observational study using the IBM Explorys database, a pooled, de-identified clinical cohort of more than 60 million U.S. patients. According to the researchers, the database collects aggregated, standardized and normalized clinical information on patients from electronic health records, all of which are updated in real time.
Merjanah and colleagues used ICD-9 codes to identify patients with SLE and myasthenia gravis, with SLE cases additionally requiring at least two rheumatologist visits to confirm among those aged 18 years or older. For the control group, the researchers included adults without myasthenia gravis.
In their analysis, Merjanah and colleagues further stratified the cohorts based on age, race, sex, smoking status, thymectomy and autoimmune and miscellaneous comorbidities. The index date was defined as the date of SLE diagnosis in patients with myasthenia gravis. The researchers also performed a chi-square test between the two groups and calculated odds ratios.
According to Merjanah, there were 26,110 patients with myasthenia gravis, out of a total of 59,896,040 active patients. Among those with myasthenia gravis, 1.42% had a diagnosis of SLE, compared with 0.11% among the 59,869,730 control patients. Those with myasthenia gravis demonstrated an increased odds for having SLE (OR = 13.38; 95% CI, 2.08-14.84). Female sex, African American race, thymectomy, autoimmune disease and miscellaneous comorbidities were all significantly more common in patients with myasthenia gravis who developed SLE, the researchers wrote.
In addition, among patients with myasthenia gravis, those who underwent thymectomy demonstrated an increased risk for SLE compared with those who did not receive the procedure (OR = 3.11; 95% CI, 2.12-4.55).
“To date, this is the largest retrospective study evaluating the association between lupus and myasthenia gravis,” Merjanah said. “Myasthenia gravis patients should be evaluated for coexistent lupus, especially in post-thymectomy patients or African American young women with a history of other autoimmune diseases. Assessment of myasthenia gravis is suggested in lupus patients with unexplained muscular weakness and fatigue.”
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Merjanah S. Association Between Systemic Lupus Erythematosus and Myasthenia Gravis: A Population-Based National Study. Presented at: North American Young Rheumatology Investigator Forum; August 11, 2021, Destin, Florida (hybrid meeting).
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