Could there be an association between Hashimoto's thyroiditis and demodex infestation?

Background: Human demodex mites are parasites that live in the pilosebaceous unit and can result in the disease demodicosis. While demodicosis may occur as a primary skin disease; immunosuppression, and topical or systemic immunosuppressive treatments can cause secondary demodicosis. It is known that thyroid hormones may cause skin changes, such as xerosis, and thereby may also modulate immune responses in the skin.

Objectives: The aim of this study is to investigate whether or not that the changes occurring in the skin of patients with Hashimoto's Thyroiditis (HT) predispose to demodex infestation.

Methods: Seventy-eight patients being followed for a diagnosis of HT at Kocaeli University Endocrinology Outpatient Clinic, between January 2019 and March 2020, constituted the patient group. The control group consisted of 41 patients who did not have any chronic systemic or dermatological disease and were shown to have no thyroid disease by laboratory tests. Demodex intensity in the malar regions of the patient and control groups was determined using the standardized skin surface biopsy (SSSB) method and compared with each other.

Results: HT patients were significantly more likely to have increased demodex density and suggestive SSSB results than the controls (p < 0.001, p = 0.012, respectively). A significant correlation was found between demodex intensity and the findings of xerosis (p = 0.010, p = 0.011) and spiny follicular papules (p = 0.008, p = 0.008) in the patient or control groups, respectively. However, a significant correlation was identified between the demodex density and the symptoms of burning-stinging (p = 0.028), and feelings of dryness (p = 0.018) roughness (p = 0.028) only in the control group.

Conclusion: Xerotic skin and/or impaired immune responses as a result of autoimmune changes in patients with HT may lead to secondary demodicosis.