Constipation is a well-recognized gastrointestinal symptom in patients with untreated hypothyroidism. Although thyroid function tests are recommended to exclude hypothyroidism in patients with constipation, there have been no reports to determine the causal relationship between thyroid function and constipation. The aim of this study was to determine the prevalence of hypothyroidism in constipated patients and the clinical features of constipation associated with hypothyroidism.

A total of 1,481 constipated patients were included. These patients were divided into overt hypothyroidism, subclinical hypothyroidism, and normal thyroid function groups based on thyroid function tests. We reviewed the clinical presentation, anorectal function, colonic transit time, defecographic findings, and response to biofeedback therapy.

The prevalence of overt and subclinical hypothyroidism was 0.41% (men, 0.36%; women, 0.53%) and 1.76% (men, 1.28%; women 2.03%), respectively. There were no differences in total or segmental colonic transit times and subtypes of constipation among the normal thyroid function (n=54), overt hypothyroidism (n=4), and subclinical hypothyroidism groups (n=21). On anorectal manometry, the prevalence of dyssynergic defecation did not differ between the three groups. Rectal hyposensitivity was more frequent in the overt hypothyroidism group (overt hypothyroidism group, 50.0%; subclinical hypothyroidism group, 19.0%; normal thyroid function group, 20.4%) without statistical significance ( P =0.372).

The prevalence of overt and subclinical hypothyroidism in constipated patients was very low. The colonic transit time is not affected by thyroid function.