Apples to Oranges
A critical look at a Turkish study on polyautoimmunity and Celiac disease.
I’m just really puzzled by this 2017 Turkish study that aims to explore age-based polyautoimmunity prevalence in participants with Celiac disease. All of the other studies on polyautoimmunity and Multiple autoimmune syndrome, reviewed so far, define polyautoimmunity as two or more autoimmune diseases, meeting study classification criteria, that occur in one person. That definition of polyautoimmunity has always included the primary autoimmune disease studied. For example, the studies on Systemic Lupus Erythematosus and polyautoimmunity considered the study participant to meet the criteria for polyautoimmunity if they had Systemic Lupus Erythematosus and one other autoimmune disease that met the study classification criteria.
This study is different. The authors don’t include Celiac disease in their definition of polyautoimmunity, even though participants had to have biopsy-confirmed Celiac disease in order to be included in the study. Their unique definition goes unexplained and significantly affected their results on age-based polyautoimmunity. Their results showed that their younger study cohort (under age 65) had a greater prevalence of polyautoimmunity than their older (age 65 and older) study cohort. By their definition, participants met the qualification for polyautoimmunity if they had Celiac disease (required for inclusion in the study), and two other autoimmune diseases. In all other studies, this definition would meet the criteria for Multiple autoimmune syndrome, having three or more autoimmune diseases. If you refer to the line of the study’s chart below “With/without AID (%)” you’ll be able to see what I mean.
According to the chart, 44 study participants in the older age group have an autoimmune disease (AID). Although this is not addressed explicitly in the text of the study, this line cannot refer to Celiac disease, since the study states that only participants with biopsy-confirmed Celiac disease were included in the study. Therefor, all 66 older patients have Celiac disease, and 44 out of 66 participants have another autoimmune disease. By the definition of polyautoimmunity in all other studies, this would mean that 66.7% of older participants have polyautoimmunity compared to 24.9% polyautoimmunity prevalence rate in younger participants. This is consistent with findings in other studies that show that the risk of polyautoimmunity increases with age.
The results become more confusing still when looking at the authors’ definition of polyautoimmunity and multiple autoimmune syndrome, as it relates to the numbers they report. So much so that I don’t trust my interpretation of them. My other criticism of the study is that it doesn’t specify the study classification criteria used to determine the presence of other autoimmune diseases in the study participants.
Despite these two really fundamental criticisms, there were a couple of nuggets of interest in this study, which I review below. The next study in my series is also by these authors, and once I have a chance to review it, I plan to write to the authors to explain their reasoning for their unique definitions of polyautoimmunity and multiple autoimmune syndrome. If they get back to me, I’ll include their answers here.
Area of Investigation
Multiple Autoimmune Syndrome: when one person meets the study classification criteria for three or more autoimmune diseases.
Study Title
Similarities and differences between older and young adult patients with celiac disease
Results
This study is a comparison of old and young patients with biopsy-confirmed celiac disease, with particular emphasis placed on co-existing autoimmune disease.
There were 66 participants in the older group, 50 of whom were women. 277 participants in the younger group, 207 of whom were women. Only eight (12.2%) participants in the older group had digestive symptoms as clinical clues leading to a diagnosis of Celiac disease. The remaining 58 participants had non-digestive clinical clues, including iron, Vitamin B12 and/or Vitamin D deficiency, that led to a diagnosis of Celiac disease. Participants in the older group most commonly had concurrent diagnoses of Autoimmune thyroid disease, Type 1 diabetes and Sjogren’s syndrome.
Why it Matters
If this study’s definitions were consistent with the definitions of other studies on polyautoimmunity and multiple autoimmune syndrome, then this study’s findings confirm that the risk for polyautoimmunity increases with age. It’s also important that this study indicates that older patients either do not have classic gastrointestinal symptoms associated with celiac disease, do not report classic symptoms, or are not recognized by their healthcare providers to have classic symptoms. Therefor, screening for common lab deficiencies may be the most effective way to screen for Celiac disease in older patients, and Celiac disease should be suspected when values are abnormal. Older patients have had a lifetime of exposure to wheat gluten, with plenty of opportunity to develop autoantibodies, with intestinal damage, because of it.
Study Type
For reference, I have ranked medical study types in order of least likely to be affected by hidden bias to most likely to be affected. Those studies that are most likely to be affected by hidden bias should be taken seriously, but not given the same weight as studies that are less likely to be affected by hidden bias. This study’s type appears in bold below.
Clinical Trial
Observational Study
Prospective
Retrospective
Cross-sectional
References
Kalkan Ç, Karakaya F, Soykan I. Similarities and differences between older and young adult patients with celiac disease. Geriatr Gerontol Int. 2017 Nov;17(11):2060-2067. doi: 10.1111/ggi.13020. Epub 2017 Apr 10. PMID: 28393451.