Thyroid in Bariatric Surgery
Condition: Thyroid; Obesity; Insulin Resistance; Autoimmune Thyroiditis
MeSH terms: Insulin Resistance; Thyroid Diseases; Thyroiditis; Thyroiditis, Autoimmune; Hashimoto Disease
Study type: Interventional

Summary: 
      This study is expected to provide novel data regarding potential structural and functional
      changes of the thyroid gland in morbidly obese adults following significant weight loss
      through bariatric surgery. These data will complement evidence from epidemiological studies
      regarding the association of obesity and alterations in thyroid function. Potentially this
      study may justify further longer-term studies regarding the effects of weight gain and/or
      weight loss on the morphology of the thyroid gland and could help to form recommendations
      regarding follow-up investigations for the thyroid in morbidly obese patients.
    

Detailed description: 
      Alterations in thyroid function are reported in obesity. Thyroid hormones and
      thyroid-stimulating hormone (TSH) concentrations have been variously described as normal,
      elevated, or low in morbidly obese patients compared with normal weight controls. However, it
      is a common observation that a significant proportion of patients with morbid obesity display
      slightly increased serum levels of TSH, while even relatively mild elevations of serum TSH
      are associated with an increase in the occurrence of obesity. Of note, abnormalities in
      thyroid function and TSH mostly normalize after weight loss, suggesting that these
      biochemical alterations are reversible. Despite uncertainty regarding the underlying
      mechanisms, it has been suggested that neither autoimmunity nor iodine deficiency seems to
      play a critical role. Several alternative mechanisms leading to hyperthyrotropinemia have
      been hypothesized, which include impaired feedback due to decreased number of
      triiodothyronine (T3) receptors in the hypothalamus, and variations in peripheral deiodinase
      activity. Leptin, in addition to regulating body weight and satiation, has also been shown to
      mediate the production of pro-TRH in cultured fetal rat hypothalamic neurons. Partial
      regulation of TSH by leptin has been also reported in humans. In addition, peripheral thyroid
      hormone metabolism appears to be reflected by the ratio of T3 to reverse T3 (rT3)
      (T3/rT3-ratio). We have shown that the T3/rT3-ratio is significantly increased in insulin
      resistant patients compared to their insulin sensitive partners despite comparable TSH
      values. Given that obesity is strongly associated with insulin resistance, and thyroid
      hormones are known to modulate carbohydrate metabolism, e.g. by affecting cellular glucose
      uptake, possible changes in the T3/fT3 ratio following weight loss after bariatric surgery
      could be of interest.

      Data from cross-sectional studies further indicate that the thyroid structure of obese
      patients can be also affected, independent of the existence of autoimmune thyroiditis as
      indicated by the presence of auto-antibodies such as TPO. Ultrasound (US) scans are able to
      accurately characterize the echographic structure of thyroid tissue, in addition to
      estimation of thyroid volume and identification of non-palpable thyroid nodules. The typical
      normal thyroid parenchyma has a distinct high echo density due to the follicle structure,
      which contrasts well with tissue of the collar muscles. The interface between thyroid cells
      and the colloid exhibits elevated acoustic impedance, causing high-frequency acoustic waves
      to be reflected back to the US probe. However, in autoimmune thyroid diseases both
      lymphocytic infiltration and disruption of normal tissue architecture cause a reduction in
      thyroid echogenicity, whereas other tissues close by such as muscle tissue appear to remain
      unaffected. Only few previous studies reported on the morphology of the thyroid gland in
      adults with morbid obesity. Given that thyroid function has been reported to return to normal
      after weight loss, research questions are also raised about the potential reversibility of
      thyroid structural abnormalities following substantial weight loss in previously morbidly
      obese patients.
    

Intervention name(s): Bariatric surgery
Intervention type(s): Procedure
Intervention description(s): patients who had received treatment with bariatric surgery for medical reasons
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: Bariatric surgery; Leptin; Thyroid function tests