The increasing dysfunction of the thyroid gland, particularly hypothyroidism, and its multifaceted effects on the gastrointestinal tract, such as potential changes in hormonal receptor sensitivity, neuromuscular disorders, and myopathy caused by infiltration of the colonic wall, lead to impaired bowel function. Although constipation remains the most common gastrointestinal complaint in hypothyroidism, hypomotility may contribute to excessive bacterial growth in the small intestine and the development of diarrhea.

The aim is to study the role of visceral hypersensitivity and cortisol levels in patients with intestinal dysfunction in coexisting hypothyroidism and in those with constipation or diarrhea without thyroid dysfunction.

Materials and methods. A total of 41 patients with hypothyroidism were examined, of whom 24 were diagnosed with persistent constipation and 17 with diarrhea, along with 36 patients with irritable bowel syndrome (IBS) (control group), of whom 22 had constipation and 14 had diarrhea. In all the patients, visceral hypersensitivity was assessed using the Visceral Sensitivity Index (VSI), and serum cortisol levels were measured by enzyme-linked immunosorbent assay (ELISA) using commercial kits from Sanguin (USA). Fecal calprotectin levels were assessed with the Human CALPE (Calprotectin) ELISA KIT by Elabscienсe (USA).

Results. VSI was higher in patients with hypothyroidism and diarrhea and scored 66.0 (61.0; 68.0) points. In individuals with IBS and diarrhea without thyroid dysfunction, VSI was 58.0 (54.0; 62.0) points. Meanwhile, VSI was 65.0 (60.0; 69.0) points in patients with constipation due to hypothyroidism, whereas in IBS patients without thyroid dysfunction, it was significantly lower – 24.0 (22.0; 26.0) points (p < 0.05). In the control group without bowel and thyroid pathology, VSI scored 15.0 (12.0; 18.0) points. The serum cortisol level in patients with hypothyroidism and diarrhea was 305.41 (270.24; 309.3) nmol/L, while in patients with IBS and diarrhea without thyroid dysfunction, it was 211.0 (205.0; 222.5) nmol/L. In patients with constipation due to hypothyroidism, the serum cortisol level was 310.625 (308.440; 337.285) nmol/L, whereas in IBS patients with constipation, it was 178.0 (172.0; 187.5) nmol/L. For healthy individuals, the cortisol level was 158.0 (152.0; 167.5) nmol/L. A direct correlation has been found between a high degree of visceral sensitivity and cortisol levels in patients with hypothyroidism and constipation, as well as an inverse correlation in patients with hypothyroidism and diarrhea. The obtained data may indicate a shift towards hypersensitivity and the development of symptoms characteristic of IBS.

Conclusions. Visceral hypersensitivity is observed both in cases of diarrhea developing against the background of hypothyroidism and in irritable bowel syndrome with a similar clinical presentation. At the same time, in cases of constipation associated with hypothyroidism, hypersensitivity is also present but tends to be less pronounced in IBS with constipation. Patients with hypothyroidism, regardless of the presence of constipation or diarrhoea, have an increase in blood cortisol levels, while in some variants of IBS, they do not differ significantly from those of healthy individuals. A direct correlation was found between a high degree of visceral hypersensitivity and cortisol levels in hypothyroid patients with constipation and the opposite in hypothyroid patients with diarrhoea.