D2.190 - Unmasking Autoimmunity: A Case of Thyroiditis Emerging After Allergy Immunotherapy
Case report
Background
Subcutaneous immunotherapy (SCIT) is an effective allergy treatment that promotes immune tolerance. However, its impact on the broader immune system remains incompletely understood. Rarely, SCIT has been associated with autoimmune thyroiditis, including Hashimoto’s thyroiditis. Could SCIT inadvertently trigger an immune response leading to thyroid dysfunction in susceptible individuals?
Case Presentation
A 44-year-old woman with allergic rhinitis underwent SCIT for Parietaria pollen. After 14 months, she developed fatigue, weight fluctuations, and palpitations. Laboratory tests revealed an elevated thyroid-stimulating hormone TSH level of 7.8 mIU/L, low free T4 of 8.5 pmol/L, and significantly increased anti-thyroid peroxidase TPO antibodies at 744 IU/mL, consistent with autoimmune thyroiditis. A thyroid ultrasound showed thyroid gland inflammation and structural abnormalities, including hypoechoic areas, irregular contours, and nodular formations. The patient had no prior thyroid issues or autoimmune conditions, making this onset particularly concerning. Given the timing, SCIT was suspected as a potential trigger. Treatment with levothyroxine improved her symptoms, and SCIT was discontinued.
Discussion
The link between SCIT and autoimmune thyroiditis may involve immune cross-reactivity. SCIT modulates T-cell responses, usually promoting tolerance, however, in genetically predisposed individuals, it might inadvertently trigger thyroid autoimmunity. Molecular mimicry, where allergens share structural similarities with thyroid proteins, could lead to an autoimmune response. Additionally, an imbalance in immune regulation during SCIT may contribute to thyroid dysfunction.
Conclusion
While rare, autoimmune thyroiditis following SCIT is a potential concern. Clinicians should be vigilant when patients on SCIT develop unexplained fatigue, weight changes, or palpitations, particularly if they lack a prior thyroid history. Thyroid screening might be warranted in such cases, especially for patients with a family history of autoimmunity. Further research is needed to clarify whether routine thyroid monitoring should be implemented for at-risk individuals.
