Hashimoto’s Thyroiditis (HT) and Celiac Disease (CD) are both chronic conditions where the body’s immune system mistakenly attacks its own tissues. HT is an autoimmune disorder primarily targeting the thyroid gland, leading to inflammation and often resulting in an underactive thyroid, known as hypothyroidism. Celiac Disease is a separate autoimmune condition where the ingestion of gluten, a protein found in wheat, rye, and barley, triggers an immune response that damages the lining of the small intestine.
The Nature of Autoimmune Co-occurrence
Hashimoto’s Thyroiditis does not directly cause Celiac Disease, nor vice versa, but they frequently appear together in the same person. This association is an example of polyautoimmunity, which is the tendency for an individual with one autoimmune condition to develop others. The immune system’s dysfunction is often systemic, meaning the susceptibility to misplaced self-attack is not confined to a single organ. The prevalence of Celiac Disease in people with HT is significantly higher than in the general population, with co-occurrence rates ranging from approximately 2% to 15%. This shared underlying mechanism explains why testing for one condition is often recommended upon the diagnosis of the other.
Genetic and Environmental Common Ground
The reason for the co-occurrence of Hashimoto’s Thyroiditis and Celiac Disease lies in shared biological susceptibility factors, particularly in the genetic makeup of the individual. Nearly all people with Celiac Disease, and a notable portion of those with HT, carry specific variants of the Human Leukocyte Antigen (HLA) genes. These genes are essential for immune system function and are responsible for presenting foreign invaders to T-cells. Specifically, the HLA-DQ2 and HLA-DQ8 alleles are strongly associated with CD and are over-represented in patients with autoimmune thyroid disorders.
While possessing these HLA alleles is necessary for CD to manifest, it is not sufficient, meaning genetic predisposition requires an additional trigger. Environmental factors are believed to provide this necessary trigger in genetically susceptible individuals. One proposed factor is increased intestinal permeability, often referred to as “leaky gut,” which allows substances like gluten to pass through the intestinal barrier and interact with the immune system. Infections, prolonged stress, or other environmental exposures may also contribute to the immune system misfiring.
Screening and Management Considerations
Given the statistically increased co-occurrence, current clinical recommendations suggest screening for Celiac Disease when a patient is diagnosed with Hashimoto’s Thyroiditis, and vice versa. Celiac Disease screening primarily uses a blood test measuring Tissue Transglutaminase IgA (tTG-IgA) antibodies, which must be performed while the patient is consuming gluten. If serology is positive, a small intestine biopsy is often required to confirm the diagnosis. Screening for HT involves measuring thyroid-stimulating hormone (TSH) and checking for anti-thyroid peroxidase (TPO) antibodies.
Management
Management of the two conditions is distinct but complementary. Hashimoto’s Thyroiditis is managed with levothyroxine, a synthetic thyroid hormone, to restore normal thyroid function. The only treatment for Celiac Disease is a strict, lifelong adherence to a gluten-free diet. For patients with both conditions, removing gluten may improve nutrient absorption, which can enhance the effectiveness of thyroid medication.