Endocrine Abstracts

Introduction

It is recommended to determine levothyroxine (LT4) dose individually in patients with hypothyroidism. However, higher doses of LT4 therapy are required to achieve target TSH levels in significant number of patients. Oral LT4 absorption occurs in the small intestine, especially in the jejunum and proximal ileum, while a small amount is absorbed in duodenum. Causes of LT4 malabsorption include helicobacter pylori infection, chronic atrophic gastritis, celiac disease, lactose intolerance, pancreatic insufficiency, cirrhosis, nephrotic syndrome, gastrointestinal malabsorptive surgical procedures, short bowel syndrome, drug and diet-related interactions. Here, we present a case of ileostomy with multiple small intestine resection, which is a rare cause of LT4 malabsorption.

Case

A 59-year-old male patient was consulted to our endocrinology clinic due to high TSH levels before ileostomy closure from the gastrosurgery clinic. The patient underwent total thyroidectomy in 2009 due to medical recurrence Graves disease and had postoperative hypothyroidism, he was euthyroid with levothyroxine treatment of 175 µg/day. With the diagnosis of rectal cancer in January 2020, the patient underwent a low anterior resection and colostomy. Pathology reported as moderately differentiated adenocarcinoma, followed by chemotherapy and radiotherapy. In October and November 2020, segmental small bowel resection due to radiation ileitis, ileus was performed. Ileostomy was performed in November 2020 for the patient whose colostomy did not work for a long time. Despite medical treatment, ileostomy was planned to be closed after 8 weeks due to the daily discharge of 14 times from ileostomy. It was consulted preoperatively in January 2021 due to TSH:66 mU/l. The oral levothyroxine dose was gradually increased from 150 µg/day to 350 µg/day due to increase in TSH to 80 mU/l, despite appropriate replacement of levothyroxine. When his TSH level was 37 mU/l, free T4 and T3 were normal with 350 µg/day oral levothyroxine, ileostomy was closed in February 2021. The patient’s free T4 and T3 values started to increase in 3 days after ileostomy closure, and levothyroxine dose was gradually decreased. The patient has been followed euthyroid with levothyroxine döşe of 150 µg/day.

Conclusion

Intestinal absorption problems may cause high-dose LT4 therapy. The decrease of the intestinal absorption surface and the shortening of the intestinal transit time can be considered among malabsorption mechanisms. Further research should be conducted in the presence of increased serum TSH levels despite high dose LT4 therapy.