Demodicosis and Thyroid Autoimmunity: Unravelling the Connection

Demodex mites are commensal ectoparasites in human pilosebaceous units that become pathogenic at high levels, causing demodicosis, which may be primary or secondary to immunosuppression. Thyroid hormones, with skin receptors, impact immune functions and epidermal inflammation. We hypothesised that skin features like xerosis and papular lesions, common in demodicosis, may also appear in autoimmune thyroid diseases, with immune dysregulation increasing Demodex colonisation. We recruited 201 patients with demodicosis or rosacea at Kayseri City Education and Research Hospital. Thyroid hormones (TSH, T3, and T4), anti-TPO antibodies, and demodex count measured by Standard Superficial Skin Biopsy were assessed. Patients were classified as Type 1 (erythema, telangiectasia, and rough skin) or Type 2 (papules and pustules) demodicosis. Results revealed that patients with elevated anti-TPO levels had significantly higher demodex counts (p < 0.05). Demodex positivity and anti-TPO levels were strongly associated with Type 2 demodicosis (p < 0.001, p = 0.008). There was a positive correlation between demodex count and anti-TPO (r = 0.144, p = 0.043), with a predictive value for anti-TPO positivity (p = 0.004). Our findings suggest that increased demodex counts in Type 2 demodicosis correlate with autoimmune thyroid disease risk, highlighting the potential of combined Demodex count and thyroid antibody assessments for early diagnosis.