BACKGROUND
According to the American Society for Metabolic and Bariatric Surgery, 179,000 bariatric surgeries were performed in the United States in 2013. The two most common bariatric procedures are including Roux-en-Y gastric bypass, where part of the stomach is removed (34.2% of surgeries) and gastric sleeve procedures, where the stomach is constricted but remains intact (42.1% of surgeries). Obesity and hypothyroidism often occur in the same patient and ~18% of bariatric surgery patients require thyroid hormone therapy. It has previously been demonstrated in patients not taking thyroid hormone that both T3 and TSH are elevated in obese individuals and that levels of TSH, T3, or both tend to fall after either diet- or surgery-induced weight loss. A recent study demonstrated that average levothyroxine doses decreased proportionally with decreases in lean body mass in hypothyroid individuals following bariatric surgery. This study further examines the levothyroxine dose requirements after bariatric surgery in a population that received mainly gastric sleeve surgery.

THE FULL ARTICLE TITLE:
Zendel A et al. The impact of bariatric surgery on thyroid function and medication use in patients with hypothyroidism. Obes Surg. March 2, 2017 [Epub ahead of print].

SUMMARY OF THE STUDY
The medical records of all patients who underwent bariatric surgery between 2009 and 2014 at a single center in Tel Aviv were reviewed. A total of 93 patients with a diagnosis of hypothyroidism made prior to their surgery (5.1% of all individuals in the database) were included. The diagnosis of hypothyroidism was made by primary care providers prior to referral for bariatric surgery and based on elevated serum TSH values on a minimum of two occasions. No patients had a history of thyroid surgery or radioactive iodine therapy. Body-mass index (BMI), TSH, free T4, and levothyroxine doses were assessed at baseline and at 6 and 12 months after bariatric surgery. Thyroid hormone dosing was managed by clinical providers and was not done according to a study protocol.

Of the 93 study participants, 85 (91%) were women and the average age at surgery was 46.6 years. The majority of patients (77 (83%)) underwent gastric sleeve surgery. The remaining 16 patients underwent Roux-en-Y gastric bypass. The average baseline BMI was 43.7 and declined to 34.4 at 6 months and to 29.8 at 12 months. Most patients (89%) were treated with L-T4 prior to surgery. The average baseline TSH was 3.9 mIU/L; this decreased to 3.0 mIU/L at 6 months and subsequently stabilized at 3.0 mIU/L at 12 months. The baseline average free T4 was 13.7 pmol/L. This increased to 15 pmol/L at 6 months and to 14.9 pmol/L at 12 months. The average daily dose of L-T4 at baseline was 98.4 μg. This decreased to 89.7 μg at 12 months. Ten patients (12%) required lowered levothyroxine doses and 11 patients (13%) stopped levothyroxine treatment altogether following their bariatric procedures. The likelihood of decreased levothyroxine dose requirement did not differ by age, sex, baseline BMI, or baseline levothyroxine dose.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study confirms that levothyroxine requirements in obese hypothyroid patients decreases after bariatric surgery, whether it is gastric bypass or gastric sleeve surgery. The average dose decreased ~9 mcg per day. This study shows that all hypothytoid patients need serial TSH monitoring after bariatric surgery.

— Alan P. Farwell, MD, FACE

ATA THYROID BROCHURE LINKS

Hypothyroidism (Underactive): https://www.thyroid.org/ hypothyroidism/

Thyroid and Weight: https://www.thyroid.org/ thyroid-and-weight/

Thyroid Hormone Treatment: https://www.thyroid.org/ thyroid-hormone-treatment/

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