Association between asthma and autoimmune disorder myasthenia gravis: meta-analysis

Bangkok – A recent meta-analysis suggests there is an association between asthma and the less common autoimmune disorder myasthenia gravis (MG). If the association is validated, it may offer more clues relating to suspected connections between certain types of asthma and underlying autoimmune disorders. The findings come from a meta-analysis of studies by researchers in Thailand involving both diseases with results published in Lung. “Establishing the association between asthma and MG would lead to a better understanding of their pathogenesis,” the researchers wrote. And along with that, possible improved prevention and management of both diseases. READ: Rhinitis: various causes, but treatable MG is an autoimmune disease characterized by skeletal weakness, either general or localized and usually includes eye muscles. Its incidence is between five to 30 cases per 100,000 population and is likely caused by a combination of immunologic, genetic and environmental factors. The authors stated asthma and MG may share some common immunopathic pathways. Some studies show MG patients have higher serum levels of CD23, a protein that plays a small role in IgE synthesis, antigen presentation and B-cell activation. IgE is believed to contribute to Type-2 asthma and other allergic conditions. The two conditions also have some overlapping genetic features. In addition “asthma and MG may share some common environmental risk factors. Viral infections are important triggers of acute wheezing episodes and the inception and exacerbation of asthma. They also have been suspected to play a role in MG,” they wrote. To be included in the study, eligible cohort studies had to consist of one cohort of asthmatics and another cohort without asthma. Studies also had to report the risk of incident MG between the groups. Eligible case-control studies had to include cases with MG and controls without MG. Then the studies had to explore patient history of asthma. A total of two cohort studies and three case-controlled studies were eligible for inclusion. The analysis showed patients with asthma had about 1.4 times higher odds of having MG, which the researchers said was significant. The researchers acknowledged a weakness of the study was having to rely on diagnosis codes from administrative databases to identify and diagnose both asthma and MG with no information on endotypes, phenotype or severity. A weakness of many studies is that asthmatics are often not well defined, according to Dr. Dilini Vethanayagam, a professor of medicine at the University of Alberta. And in practice, studies show upwards of 30% of patients being treated for asthma do not even have the disease. “There are many causes of dyspnea or shortness of breath, often misconstrued as asthma,” she said. In 2014 she reported a single case of asthma and MG in the Canadian Respiratory Journal and pointed out that many autoimmune processes can coexist and can account for a person’s dyspnea beyond an airways disorder. It’s possible some asthma could be part of, or an indicator of an underlying autoimmune disorder resulting from specific inflammatory pathways. This could be the case especially in non-atopic individuals, and patients who (even after good environmental controls and medication compliance) are refractory to traditional asthma treatments, she said. Researchers in Hamilton Ontario also suggest the idea of autoimmune mechanisms in asthma should be looked at more closely. In a 2018 review in Allergy, Asthma and Immunology Research, they said there are a number of compelling features found in some asthmatics. “There is a growing body of evidence that cumulatively indicates the presence of autoimmune mechanisms underpinning disease severity in a subset of asthmatics, in particular the late-onset non-atopic severe asthmatics,” paper said. “Recent evidence of ‘granulomas’ in the lung biopsies of severe asthmatics, detection of pathogenic sputum autoantibodies against autologous eosinophil proteins… and inadequate response to monoclonal antibody therapy … in patients with evidence of airway autoantibodies,” are all clues and it is worth revisiting the role of autoimmune mechanisms.

Association between asthma and autoimmune disorder myasthenia gravis: meta-analysis

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