The category “autoimmune disease”, as with almost all other diseases, consists of conditions that run the spectrum from very common to exceedingly rare, and everything in between. These distinctions are sometimes fairly static, but more often they are rather fluid characterizations that tend to change epidemiologically and demographically over time and across global regions. Below we examine briefly some pertinent information regarding those autoimmune conditions considered to be rare in terms of incidence (how many cases are diagnosed per year) and prevalence (the overall number of cases at any one point in time) within society.
How many of the 80+ autoimmune diseases are considered rare and why?
There really is no one good answer to this question, but autoimmune conditions can be broken down into those that are more common or more rare than others. This determination is simply numerical, based on incidence and prevalence (above). It is also important to know that what is considered medically “common” may not always translate to the lay conception of this term. That is, while a certain disorder may be labeled “common” statistically, it is often likely to still be diagnosed relatively infrequently in the general population.
Of the 80+ autoimmune diseases known to exist, it might be said that the majority of them are considered rare, which unfortunately also means there is relatively little data out there documenting exactly how rare. This leads to a cycle of “chicken and egg” uncertainty on the topic. Certainly, we can count such diseases as multiple sclerosis, rheumatoid arthritis and lupus as more common, with the numbers gradually decreasing until reaching such conditions as anti-NMDAR encephalitis, Cold Urticaria, and Goodpasture’s syndrome, which are decidedly more rare.
Are there some autoimmune diseases that used to be rare but are now very common?
Again, in a certain sense, all autoimmune conditions used to be fairly rare, as it has been noted that many have been steadily increasing in prevalence over recent years. Whether it is because of a lack of recognition, a lack of existing cases or both, autoimmune diseases such as celiac disease were previously unheard of in most circles, outside clinical specialties. Today, it is difficult to find anyone who hasn’t at least heard of gluten sensitivity. And disorders that were relatively prominent before, such as type-1 diabetes, have begun to skyrocket in the population of developed countries. It is also important to keep in mind that the majority of autoimmune diseases are considerably more common in women, making them relatively rare in males.
One explanation for the large increase in autoimmune disease cases within the developed world involves the hygiene hypothesis, which we have discussed previously in past articles. Briefly, this line of thinking suggests that the reason for such increases in certain autoimmune disease involves the fact that we may have become “too clean” for our own good. That is, by becoming so good at antiseptic techniques, antimicrobial treatments and general hygiene, we may have inadvertently caused our own antibodies, left with fewer external concerns, to turn their focus inward, attacking instead those internal tissues that appear similar to outside invaders. This is a mechanism known as molecular mimicry.
What does it mean to be diagnosed with a rare autoimmune disease from a treatment standpoint?
Unfortunately, many times this means that the condition hasn’t been studied as extensively as more prominent diseases, which in turn means that pharmaceutical companies likely haven’t developed as many effective treatments. Sometimes, if the prevalence is so low as to not provide a profit incentive to these corporations, there is barely any available research or specific therapies.
However, there is some good news too. As autoimmune diseases continue to be studied more and more extensively, researchers have found that many treatments used for more common ailments also demonstrate some effectiveness for more rare conditions. This is based on the common pathology involving antibodies attacking one’s own tissues, despite a lack of complete understanding of the exact mechanisms involved in each illness.
Do the rare diseases have common traits (other than their shared autoimmune status) that could help aid researchers or apply treatments of one disease to others?
Not really, at least on a clinical level. There is some commonality in that many appear to focus on connective tissues within the body, but this is still a very broad target. Otherwise, the major connection among all of these 80+ disorders is their shared autoimmune origin. We can only hope that researchers on the forefront of autoimmune investigation will find other connections in the future that might aid in our understanding and treatment of these conditions.
About the Author
Dr. Rothbard is a professional medical writer and consultant based in New York City, specializing in medical education articles targeted at a variety of audiences, from children through clinicians. After leaving medicine, he worked as a biology and medical science educator for several years, before deciding to pursue writing full-time. He may be reached at [email protected].