**4. Discussion**

The COVID-19 pandemic has affected many aspects of human lives worldwide. Information about the diseases that predispose to severe and unfavorable course of COVID-19, the spectre of long-term quarantines, lack of targeted treatment or lack of medical support have been causing a huge psychological burden and generating psychological distress and sleep disorders.

Research on psychological distress and sleep disorders in patients with chronic diseases shows that they are particularly predisposed to mental health disorders [24]. The reported incidence of depression, anxiety or sleep disorders varies widely, depending on the population studied and diagnostic tools. In an analysis conducted by Pumar et al., it was noted that in patients with chronic obstructive pulmonary disease the prevalence of depression ranges from 10% to 57% and in the case of anxiety the prevalence ranges from 7% to 50% [25]. Budhiraja et al. noted sleep disorders in 27.3% of patients with chronic obstructive pulmonary diseases [26]. Other studies have confirmed the relationship between depression, anxiety and sleep disorders in patients with chronic pain, chronic neurological diseases, kidney diseases or autoimmune diseases [27–31].

The most important finding of the present study is the fact that among chronic diseases such as hypertension, diabetes, coronary artery disease, circulatory failure, dyslipidemia, chronic obstructive pulmonary disease, nicotinism, and Hashimoto's disease, it was the group of patients with Hashimoto's disease that showed a strong correlation with increased scores on ISI (r = 0.797, *p* < 0.001), GAD-7 (r = 0.766, *p* < 0.001) and PHQ-9 scales (r = 0.767, *p* < 0.001). The group of patients with Hashimoto's disease also showed significantly more frequent symptoms of anxiety, depression and insomnia compared to people without this condition (*p* < 0.001, *p* < 0.001, *p* < 0.001).

These individuals, also after the results were corrected for age, gender, hypertension, dyslipidemia and smoking, showed more than twice higher risk of aggravation of anxiety symptoms, more than 2.5 times greater increase in the severity of depression symptoms, and more than 3.5 times increase in the severity of insomnia.

Autoimmune thyroiditis often coexists with insomnia, depression and anxiety [32]. The prevalence of antithyroid autoantibodies in patients with depressive disorders is higher than in the general population. Carta et al. showed that the risk of depressive disorders in a group of patients with thyroid diseases was up to six times higher than in those without, regardless of thyroid dysfunction assessed by routine serological tests [33]. Similar results were obtained by Giynas et al. who confirmed an increased incidence of depressive disorders in a group of patients with thyroid diseases [34]. Kirim et al. pointed out an increased risk of depression in a group of patients with chronic inflammation of the thyroid gland even though its hormonal function was normal. In addition, they showed that an autoimmune inflammation of the thyroid gland can result in the failure of the thyroid gland, which in turn is a risk factor for the development of depression resistant to standard treatment [35]. Geracioti et al. described an interesting case of a patient with classic symptoms of emotionally unstable borderline personality, with co-occurring autoimmune thyroiditis, in whom mood swings and psychotic symptoms were directly related to the titer of antithyroid antibodies [36]. In a study by Huang et al., the severity of depression and insomnia were significantly correlated with low FT3 [37]. In anxiety disorders, the first symptom in patients with hypothyroidism is often generalized agitation [38]. Since this disorder commonly coexists with elevated blood pressure and tachycardia, it can be assumed that this condition leads to the development of generalized anxiety syndrome.

Suffering from an autoimmune disease can generate enormous stress, through a significant reduction in activity at home or at work, financial difficulties related to the cost of medical care and reduced income, lack of acceptance of its appearance resulting from, among other things, complications of the applied treatment, impaired interpersonal relations or loss of independence [39]. Even discreet intensification of everyday stress factors in people with autoimmune diseases affects the hypothalamic-pituitary-adrenal axis homeostasis, which leads to intensification of the disease symptoms or adversely affects its remission [40]. It seems that is why patients with Hashimoto's disease, who are aware of an increased risk of more severe symptoms of COVID-19, are most likely to develop anxiety, depression and insomnia among all chronic diseases, as confirmed by our study.

Our study had several limitations. Firstly, Hashimoto's disease was the only autoimmune disease that was included in this study, although there may be other autoimmune diseases which may induce similar psychological effects during the SARS-CoV-2 pandemic. Secondly, there is an interplay between depressive and anxiety symptoms on the one hand and the presence of insomnia symptoms on the other hand. Thirdly, as a cross-sectional study, it provided no information on any change in mental health of the respondents.
