Thyroid dysfunction is common in patients with diabetes, with a prevalence of around 17%, according to a new analysis of an Australian population.

The results add to the debate over whether patients with diabetes should undergo clinical or biochemical screening for thyroid dysfunction. The American Diabetes Association and U.K. National Institute for Health and Care Excellence guidelines do not recommend general thyroid function monitoring in type 2 diabetes, but the authors of the new study noted concerns that thyroid dysfunction could have metabolic consequences in type 2 disease.

Although the prevalence of undiagnosed thyroid disease in participants with type 2 diabetes was similar to that found in the general Australian population, the researchers, led by Kristen E. Peters, PhD, MedSc, and Timothy M.E. Davis, BMedSc MB, DPhil, of the University of Western Australia, Perth, noted in an article in Clinical Endocrinology that thyroid disease may worsen cardiometabolic risk factors, potentially giving it more significance in this population.

For their study, the researchers analyzed longitudinal data from 1,617 participants in the Fremantle Diabetes Study Phase II, of whom 8.0% had type 1 diabetes, 87.1% had type 2 diabetes, and 4.9% had latent autoimmune diabetes of adults (LADA).

All of the participants filled out questionnaires and underwent baseline fasting biochemical tests and were invited to return for biennial clinical and biochemical measures and to complete biennial questionnaires that were mailed to them. The participants were followed from 2008-2011 (baseline/recruitment period) to 2016. At baseline, 11.7% of the sample (189 of 1,617) had known thyroid disease, based on previous hospitalization of self-reported thyroid medication. Thyroid disease was more prevalent in women than in men (20.4% vs. 3.8%; P less than .001), and there was a nonsignificant trend for a higher prevalence of thyroid disease in participants with type 1 disease, compared with LADA and type 2 (16.9%, 11.4%, and 11.2%, respectively).

Among the 1,428 participants with no documented thyroid disease, 93 (6.5%) were found to have an abnormal thyroid-stimulating hormone (TSH) at baseline testing. Of those 93 participants, 79 had type 2 diabetes, 9 had type 1, and 5 had LADA; across all diabetes types, 5.1% of the participants had subclinical hypothyroidism, 1.1% had overt hypothyroidism, 0.1% had subclinical hyperthyroidism, and 0.2% had overt hyperthyroidism.

Overall, the baseline prevalence of any thyroid disease, known or previously undiagnosed, was 17.4% – 282 of 1,617 participants, of whom 23.8% had type 1 diabetes, 17.7% had LADA, and 16.8% had type 2.

At the end of year 4, serum concentrations were available for 844 participants who had no history of thyroid disease and normal baseline TSH. Over the course of the follow-up period (5,694 patient-years), 25 participants (3%) with normal baseline TSH levels had a first hospitalization for thyroid disease or started thyroid medication, including 2.8% of those with type 1 diabetes and 3.1% of those with type 2. Of the remaining 819 participants who did not have baseline thyroid disease, 3.4% developed subclinical hypothyroidism, 0.2% developed overt hypothyroidism, and 0.5% developed subclinical hyperthyroidism. In each case, there was no statistically significant difference in risk of developing thyroid dysfunction by diabetes type.

“The incidence of any new thyroid disease, including those [participants] with an abnormal follow-up TSH and those with known incident thyroid disease, was 59/844 (7.0%) during [4 years] of follow-up,” the authors noted. “The total incidence of new overt disease was 3.2% (27/844), with 7.4% (2/27) of these patients unaware of the condition. All of the patients with LADA remained euthyroid during follow-up.”

Among the limitations of the study, the authors noted, were that the identification of participants with thyroid disease depended on the available documentation in the databases the researchers used, they were not able to establish pretreatment of thyroid function in most participants with incident thyroid dysfunction, and they did not record free T3.

“Thyroid dysfunction, whether diagnosed or detected on biochemical screening, is common in diabetes regardless of type,” the authors wrote. “Subclinical hypothyroidism is the commonest form [of thyroid dysfunction], and it has a variable course. This latter observation alone makes an argument for periodic biochemical screening in all people with diabetes (not just type 1) as part of routine management.”

However, in an interview, Robert Eckel, MD, professor of medicine at University of Colorado at Denver, Aurora, said that the authors’ suggestion for routine thyroid function testing of patients with any type of diabetes may be premature. He noted that the study lacked a control group, making it difficult to justify a change in practice.

“My take-home message is that the current guidelines are probably not modified by [these findings], but the idea that 17% [of individuals with diabetes] have thyroid disease is worth noting. However, the absence of a control group limits changing recommendations based on this particular study,” said Dr. Eckel, who is also current president, medicine and science, of the ADA.

The study was supported by the National Health and Medical Research Council of Australia and the Spinnaker Health Research Foundation. The study authors did not disclose an financial conflicts.

SOURCE: Peters KE et al. Clin Endocrinol. 2020 Jan 27. doi: 10.1111/cen.14164.