CHICAGO – Hypothyroid patients who need either at least 125 mcg or 1.5 mcg/kg of levothyroxine per day in order to remain euthyroid should routinely be tested for celiac disease, Dr. Richard S. Zubarik asserted at the annual Digestive Disease Week.
In his cross-sectional study of 400 consecutive patients with hypothyroidism who underwent testing for celiac disease, 5% of those on a levothyroxine dose at or above that threshold were found to have biopsy-confirmed celiac disease.
Mass screening for celiac disease in the broad U.S. population isn’t recommended at present because the prevalence – 0.75% is deemed too low to justify such a practice. However, current national and international guidelines do recommend routine testing for case finding in selected populations known to be at increased risk of celiac disease. These include, for example, patients with asymptomatic iron-deficiency anemia, who have a celiac disease prevalence of 2.3%-5%. Thus, the 5% prevalence of celiac disease in hypothyroid patients requiring high-dose levothyroxine in order to maintain a euthyroid state is at least as high as, and perhaps higher than, the prevalence in groups having a guideline-recommended indication for testing, noted Dr. Zubarik, professor of medicine and director of GI endoscopy at the University of Vermont, Burlington.
Bruce Jancin/Frontline Medical News
Dr. Richard S. Zubarik
Testing involves a simple serologic test for tissue transglutaminase. An elevated level triggers endoscopy with duodenal biopsies. A positive biopsy confirms the diagnosis and warrants initiation of a gluten-free diet.
The 400 consecutive patients on treatment for hypothyroidism in Dr. Zubarik’s study averaged 59 years of age, and 82% were women. Thirty percent of participants required 125 mcg or more of levothyroxine, and 29% needed at least 1.5 mcg/kg daily in order to maintain euthyroid status. Dr. Zubarik and his coinvestigators selected those doses as their threshold in the cross-sectional study because their earlier retrospective study had suggested patients requiring that much levothyroxine might have an increased prevalence of concomitant celiac disease (Am. J. Med. 2012;125:278-82). The group requiring an elevated dose and those who were able to remain euthyroid on lower doses were similar in age, sex, weight, body mass index, and the prevalence of diabetes.
All subjects took a serologic tissue transglutaminase test, and those with an elevated level underwent endoscopy with biopsies.
Eight of the 400 patients had an elevated serum tissue transglutaminase level, and seven of the eight were subsequently confirmed as having biopsy-proven celiac disease. Six of the seven patients with celiac disease met or exceeded the levothyroxine dose threshold.
Gastrointestinal symptoms weren’t helpful in differentiating the hypothyroid patients with and without celiac disease. Scores on the Gastrointestinal Symptom Rating Scale weren’t significantly different between the two groups.
Malabsorption of vitamins, minerals, nutrients, and medications is not uncommon in patients with celiac disease, which accounts for the increased disease prevalence seen among patients with iron-deficiency anemia. Whether the increased prevalence of celiac disease among hypothyroid patients requiring elevated doses of levothyroxine is the result of levothyroxine malabsorption or perhaps a consequence of more severe hypothyroidism being present in patients with concomitant celiac disease is an unanswered question Dr. Zubarik plans to study.
The association between thyroid disease and celiac disease is independent of gluten exposure and most likely stems from a common genetic predisposition, the gastroenterologist said.
This study was carried out free of commercial support. Dr. Zubarik reported having no financial conflicts.