A significant number of people with attention deficit/hyperactivity disorder (ADHD) and tic disorder also have one or more allergic diseases such as asthma or atopic dermatitis, show study results.
The team found that the highest prevalence of allergic diseases occurred in people with ADHD and tic disorder compared with either disorder alone. In addition, ADHD patients with three or more allergic diseases were significantly more likely to also have tic disorder than those with fewer allergic conditions.
Cell-mediated and humoral immunologic dysregulation is thought to account for the observed association between ADHD, tic disorder, and allergy, although study author Ya-Mei Bai (National Yang-Ming University, Taipei, Taiwan) and colleagues emphasize the importance of "further studies to clarify the underlying mechanisms and help us understand more about the complex etiology of ADHD, tic disorder, and their co-occurrence."
The researchers analyzed data from the Taiwan National Health Insurance Research Database collected between 1996 and 2010 to assess links between ADHD, tic disorder, and allergy.
Overall, 5811 patients with ADHD alone, 1816 with tic disorder alone, and 349 with a dual diagnosis of ADHD and tic disorder were included and compared with age- and gender-matched controls. The mean age of the participants in the four groups ranged from 15.2 to 21.9 years.
Bai and team found that allergic diseases (asthma, atopic dermatitis, allergic rhinitis, and allergic conjunctivitis) were a significant 1.64- and 2.88-fold more common in people with ADHD and tic disorder, respectively, than controls.
However, patients with both ADHD and tic disorder had the highest risk for allergic disorders, with a 3.73-fold increased risk compared with controls.
There also appeared to be a link between increasing numbers of allergic diseases in ADHD patients and their risk for having comorbid tic disorder, such that ADHD patients with one, two, or three or more allergic diseases had significant 1.87-, 2.52- and 3.73-fold increased risks for tic disorder, respectively.
Another link between ADHD, tic disorder and allergy could be through the histamine pathway, suggest the researchers, because recent evidence suggests that antihistamine drugs may be effective for treating ADHD and tic disorder.
"The potential therapeutic role of antihistamine in ADHD and tic disorder may offer a future alternative treatment choice for patients with dual diagnoses, but verification of the definite treatment efficacy requires further study," they write in the Journal of Child Psychology and Psychiatry.
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