Endocrine Abstracts

Hypothyroidism is common condition with a strong female preponderance and a UK prevalence of ~2%. It is normally treated with replacement oral levothyroxine.

Morbid obesity is a costly public health issue with a prevalence in England of ~3% with two-thirds of sufferers being female. Weight loss surgery is increasingly employed as a successful and cost effective intervention for super-morbidly obese patients (BMI >40 kg/m²) in accordance with NICE guidelines (CG43, 2010).

Our patient is a young woman with primary autoimmune hypothyroidism and co-existent super-morbid obesity (peak BMI=54.9 kg/m²) who underwent laparoscopic proximal Roux-en-Y gastric bypass surgery, subsequently achieving massive weight loss to reach a new stable BMI of 32 kg/m². Following surgery, her previously stable dose of levothyroxine of 175 μg (~0.8–0.9 μg/kg per day) was increased in a stepwise fashion in response to TSH levels indicating under-replacement. Subsequently her dose has fluctuated between 250 and 400 μg daily (~2.9–4.5 μg/kg per day) with no single dose achieving a stable biochemical euthyroidism. Adherence to treatment was self-reported to be good. The importance of temporally separating levothyroxine and other interacting medications (including iron containing micronutrient supplements given routinely after malabsorptive weight loss surgical procedures) was impressed upon the patient. Heterophile antibodies against those used in the TSH assay were tested for and excluded.

Previous studies of absorption of levothyroxine before and after gastric bypass have not shown there to be any significant worsening of the absorption profile following surgery. Our experience with this patient would suggest that this may not always be the case.

With increasing use of obesity surgery including gastric bypass procedures to combat obesity, problems with dose adjustments to thyroid hormone replacement and other pharmaceuticals with a narrow therapeutic range is likely to become a more common and potentially challenging problem in our routine clinical practice.