Exploring the Link Between Allergic Rhinitis and Autoimmune Thyroid Diseases

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Allergic rhinitis (AR) may increase the risk of developing autoimmune thyroid diseases (AITD), particularly in women, suggesting the need for thyroid screening at the time of AR diagnosis.

Previous research has pointed to an association between AR and AITD, with one study reporting a high incidence of Hashimoto’s thyroiditis (HT) among patients with AR, and another demonstrating seasonal AR was significantly high among those with Graves’ disease (GD). However, investigators noted these studies were cross-sectional in nature and recruited a small number of patients, which hindered the confirmation of such a relationship.

“We noticed in our endocrinology unit an increasing incidence of AITD among patients with AR,” wrote a team of investigators led by Magdy Mohamed Allam, MBBCH, M.D., Ph.D., a researcher associated with Alexandria University Student Hospital (AUSH), Alexandria University, Alexandria, Egypt.

To determine whether AR is a risk factor for developing AITD, investigators conducted a retrospective cohort study that analyzed the records of patients with AITD who visited AUSH between January 2017 and December 2021. AR was diagnosed based on physical examinations and medical history, with symptoms including red watery eyes, clear rhinorrhea, nasal congestion, nasal itching and sneezing.

Thyroid-related laboratory data included the thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), thyroid peroxidase antibody (TPOAb), eosinophils count, thyrotropin receptor antibody (TRAb) and immunoglobulin E (IgE).

Subjects were placed into four groups: patients with AR and HT, patients with AR and GD, patients without AR presenting with HT, and patients without AR presenting with GD.

A total of 4,515 subjects were included in the analysis, with 41.7% diagnosed with both AR and AITD. Among these patients, most were women (81%) and had a mean age of 45.71 years and a mean duration of AITD of 7.32 years.

Patients in the AR group had a higher incidence of AITD than in the non-AR group. In the AR group, the prevalence of HT was 83.7% and the prevalence of GD was 16.4%. For the non-AR group, 67.6% were diagnosed with concomitant HT and 32.37% had GD.

The risk for developing HT was increased after one year post-AR diagnosis, and the risk of developing GD was increased after two years. The duration between being diagnosed with AR and developing these conditions was generally consistent, further strengthening the potential link between AR and AITD onset.

According to multivariate-adjusted hazard ratios, patients had a higher risk of developing AITD if they had AR, had a higher blood cell count, were female and were diagnosed in November. Conversely, patients with a lower risk included those who were older at AR onset, had no medical history of AITDs, had higher vitamin D levels and were prescribed azathioprine and methotrexate.

“AR is prevalent in more than one-third to two-thirds of Egyptians,” investigators wrote. “The rapid increase in AITD prevalence cannot be explained only by genetic factors. It is suggested that environmental factors may play a role in this development, especially in cases with seasonal patterns.”

Solidifying this hypothesis, HT was more commonly diagnosed in winter months, specifically December and February, while GD diagnosis peaked during the warmer months of May and August.

Limitations of the study included the retrospective design, although investigators noted all estimates and analyses were adjusted for the cohort effect, which summarizes recall bias and the effect of the generation.

“This comprehensive study has yielded valuable insights into the relationship between AR and AITDs, specifically HT and GD,” they concluded.