Clinical Briefs
April 30, 2017 3 minutes read
Atopic Dermatitis Associated with Autoimmune Disorders
SOURCE: Andersen YM, Egeberg A, Gislason GH, et al. Autoimmune diseases in adults with atopic dermatitis. J Am Acad Dermatol 2017;76:274-280.
Atopic dermatitis has been viewed as a disorder of immune regulation primarily involving T-helper cells. The common association between atopic dermatitis, asthma, and allergic rhinitis supports the concept of shared immunologic abnormalities. But the list of autoimmune disorders linked with atopic dermatitis has expanded to include vitiligo, alopecia, lupus, and inflammatory bowel disease.
The Danish National Patient Registry provides a window of observation into the association of atopic dermatitis with other autoimmune disorders. All Danes receive lifetime universal health insurance, and the registries represent both inpatient and outpatient data.
Based on hospital discharge diagnoses of atopic dermatitis (n = 8,112) in the 1997-2012 interval, an association of atopic dermatitis was found with autoimmune disorders as well as urticaria, celiac disease, Sjogren’s syndrome, ankylosing spondylitis, and rheumatoid arthritis. These associations were stronger among smokers.
Of course, association does not prove causation. Hopefully, the immunologic links between these disorders will provide keys to their successful management.
Sickle Cell Trait Falsely Lowers Hemoglobin A1c
SOURCE: Lacy ME, Wellenius GA, Sumner AE, et al. Association of sickle cell trait with hemoglobin A1c in African Americans. JAMA 2017;317:507-515.
The recent endorsement of A1c measurements for the diagnosis of diabetes (and prediabetes) has engendered an increasingly frequent diagnosis of both disorders in symptomatic and asymptomatic individuals.
A1c accurately reflects the average exposure of hemoglobin in red blood cells to glucose over the prior 90 days.
However, if red blood cell life is foreshortened — as in hemoglobin S, hemoglobin C, thalassemia, hemolytic anemia, sickle cell disease, and others — there is insufficient red blood cell lifespan for full glycosylation to occur, resulting in a reduced A1c level that does not accurately reflect long-term ambient glucose exposure. Might sickle cell trait affect A1c?
Lacy et al performed a retrospective cohort study from a sample of adults (n = 4,620) that included both A1c and plasma glucose levels. They found that the presence of prediabetes and diabetes was underestimated substantially when A1c was the diagnostic tool in persons with sickle cell trait.
The presence of sickle cell trait appears to lead to lesser levels of hemoglobin glycosylation than occurs in control subjects. The mechanism for this effect is controversial, but may reflect reduced red blood cell lifespan.
Clinicians may wish to include additional diagnostic tests for diabetes in persons with sickle cell trait, such as fasting glucose, postprandial glucose, or oral glucose tolerance testing.
Hate Traffic? You Might Be Forgetting Something
SOURCE: Chen H, Kwong JC, Copes R, et al. Living near major roads and the incidence of dementia, Parkinson’s disease, and multiple sclerosis: A population-based cohort study. Lancet 2017;389:718-726.
As we search for remediable explanations for Alzheimer’s disease and other dementias, several epidemiologically intriguing potential culprits have emerged, including air pollution and diesel exhaust. Although such pollutants have been shown to increase neuro-inflammation and oxidative stress, neither of these effects is sufficient evidence to definitively convict them.
Chen et al performed an analysis of new onset dementia cases (n = 243,611) in Canada to determine whether there was an association between how close one lives to a highway and incident dementia.
The adjusted hazard ratio indicated a slight increased risk for new onset dementia in people who lived < 50 meters from a major road (hazard ratio, 1.07) and a smaller, but still significant, increased risk among persons who lived 50-100 meters away (hazard ratio, 1.04). The relationship was strongest for persons who lived in major cities and lived in the same site long term.
Although it’s unlikely anyone anticipates that these 4-7% relative risk increases are dominant factors in the development of dementia, perhaps they can provide mechanistic clues to the disease.
In this section: a connection between atopic dermatitis and autoimmune disorders; association of sickle cell trait with hemoglobin; and the continuing search for dementia triggers.
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