Given that type 1 diabetes (T1D) and thyroid dysfunction share a similar autoimmune etiology, it is not surprising that they are often comorbid.1 Autoimmune thyroid disorders co-occur in 17% to 30% of adults with T1D.1
Likewise, type 2 diabetes (T2D) is more prevalent in people with thyroid dysfunction than the general population.1 Hypothyroidism occurs in 6% to 20% of patients with T2D across various ethnic populations and hyperthyroidism occurs in 4.4% of patients with T2D.1
Because thyroid dysfunction symptoms are nonspecific, clinicians need to test thyroid-stimulating hormone (TSH) levels to confirm diagnosis of hypo- or hyperthyroidism.2 Laboratory values, however, may not present a full clinical picture for the clinician.
Managing Subclinical Thyroid Dysfunction
Now that thyroid function assays have greater sensitivity, subclinical cases of hypothyroidism are being detected more often. As a result, some patients with laboratory values on the borderline of disease who are now receiving treatment may not have been treated before TSH testing became so sensitive.2
“The relationship between symptoms and signs of [thyroid dysfunction] and laboratory values is complex,” said endocrinologist Jacqueline Jonklaas, MD, PhD, MPH, associate professor of medicine at Georgetown University Medical Center in Washington, DC. “One patient may have, say, mild hyperthyroidism based on numbers, but may be well compensated and not very symptomatic. Another individual with the same laboratory values may be very symptomatic. This emphasizes that the clinician can best benefit the patient and decide upon the best course of monitoring or treatment if they consider the signs and symptoms and laboratory values together, and not each in isolation.”
Drugs to Avoid in Patients With Thyroid Disease
Treating comorbid thyroid dysfunction and T2D is challenging because many antihyperglycemic agents can interfere with thyroid therapies.1 For example, TSH levels need to be monitored in patients with hypothyroidism taking metformin because the drug may lower TSH in patients taking levothyroxine.1
Likewise, liraglutide should be avoided in patients with a history of medullary thyroid cancer or type 2 multiple endocrine neoplasia because animal studies have demonstrated an increase in adenomas and hyperplasia.1 Patients with Graves ophthalmopathy and diabetes should avoid treatment with pioglitazone because of its propensity to increase eye protrusion.1
Thyroid Disease Is Common in Both T2D and T1D
In a study of 1015 patients, Maria E. Barmpari, MD, from the Hippokration General Hospital in Athens, Greece, and colleagues, sought to characterize the comorbid nature of T1D and T2D in patients with and without thyroid dysfunction.3 While there was no difference in hypothyroidism occurrence between patients with T2D and T1D (37.1% vs 43.5%, respectively; P >.05), patients with T2D were more likely to have nodular goiter (34.1% vs 18.8%, respectively; P <.05). In patients with T2D, levels of hemoglobin A1C, total cholesterol, and high-density lipoprotein cholesterol were higher in cases of comorbid hypothyroidism compared with patients with T2D who did not have hypothyroidism (P <.01 for all).3
“We don’t know yet the etiopathogenetic mechanisms in T2D and thyroid disorders, but thyroid disorders are very common in T2D, as much as they are in T1D,” said Dr Barmpari.