Many studies have established that patients with autoimmune diseases such as rheumatoid arthritis (RA), multiple sclerosis (MS), Sjögren’s syndrome, and systemic lupus erythomatosus (SLE) have an increased risk for developing another autoimmune disease, but why this happens is still not fully understood.
In a recent news report that presented data from multiple studies addressing the co-occurrence of autoimmune diseases, several explanations for the phenomenon were proposed.
In healthy individuals, immune cells protect the body from harmful substances such as bacteria, viruses, toxins, or malignant cells by producing antibodies that recognize the substances and set a course to destroy them. However, in the setting of autoimmune diseases immune cells cannot distinguish between toxic substances and healthy tissues and attack a person’s own healthy cells.
In a study published in Maedica in 2010, Dr. M. Cojocaru and colleagues reported that about 25 percent of patients with an autoimmune disease develop a second disorder. One particular association they reported is Reynolds syndrome with lupus erythematosus/lichen planus-overlap syndrome. In addition, Sjögren’s syndrome was also found to occur frequently with SLE and RA.
“Overlapping syndromes between two or more autoimmune diseases in rheumatology are not uncommon,” said Dr. Antoine G. Sreih, assistant professor of clinical medicine in rheumatology at the University of Pennsylvania. “We see this with SLE, RA, scleroderma, Sjögren’s syndrome, vasculitis and polymyositis.”
Dr. Regina Berkovich, PhD, an assistant professor of clinical neurology at Keck Medicine at the University of Southern California with expansive experience in MS, suggests that the overlap of autoimmune diseases may occur because the patients already have a dysregulation in the immune system that increases the likelihood of their antibodies to begin targeting other healthy cells.
“A second scenario is that when we use immunomodulatory drugs to treat MS, the initial landscape of the immune system changes,” she said. “When we create changes to the immune system, it may predispose them to further complications.”
According to a study published in US Neurology in 2011 by Berkovich and her team, some drugs used in MS patients seem to predispose them to a second autoimmune disorder: “The association has been noticed with interferon-based therapies. Another more recent medication that may predispose patients to autoimmune complications is alemtuzumab (Lemtrada, Genzyme). We found that if patients already had MS and one other autoimmune condition, such as psoriasis or lupus, interferon was not the best choice of drug.”
Although immunomodulatory therapies have risks, knowing which drugs make patients more susceptible to co-occurrence of autoimmune diseases may help physicians and patients make more informed choices regarding treatment.
Other researchers suggest that patients are more likely to develop autoimmune diseases because of genetic factors.
“Over the last decade, several genetic factors have been found in common between multiple autoimmune diseases,” said Emily C. Somers, PhD, an associate professor of internal medicine, environmental health sciences, and obstetrics and gynecology at the University of Michigan. “However, the particular combinations of genetic and environmental factors will influence the way that autoimmunity is expressed, or what we refer to as the disease phenotype.”
Somers, who conducted a series of population-based cohort studies, also suggests that men and women have autoimmune diseases that are different in nature possibly because endocrine derived disorders give rise to different subsets of autoimmune diseases.
“Females have a much greater risk of autoimmune disease overall compared to males, and the female excess holds true for most individual autoimmune disorders,” said Somers. “For example, 90% of lupus patients are female. Thus, the risk of developing a second disorder should be examined separately for each sex, given the higher underlying risk among females. We believe that our data support similar patterns of coexistence for both sexes, but given the rarity of autoimmune diseases in males, the associations among males are more challenging to detect.”
Together, findings suggest that there is diversity in the causes that lead to associated diseases. Still, researchers believe that the best way to treat patients with co-occurrence of autoimmune diseases and to further understand the links between the diseases, is through cooperation and collaboration of experts the different diseases.