ThyrOp: A Study of Individual Subclinical Hypothyroidism After Hemithyroidectomy for Benign Nontoxic Goiter
ThyrOp: A Study of Individual Subclinical Hypothyroidism After Hemithyroidectomy for Benign Nontoxic Goiter
The hypothesis of the study is that among patients that do not develop overt hypothyroidism
 after hemithyroidectomy, weight gain is a clinical manifestation of a postoperatively lowered
 set point of thyroid function - even if the thyroid function is lowered within the laboratory
 reference range. The investigators refer to this hypothesized condition as individual
 subclinical hypothyroidism.

 Thyroid hormones are major regulators of mitochondrial function and subclinical
 hypothyroidism affects mitochondrial activity. The aim of the study is to examine if a
 lowered set point of thyroid function after hemithyroidectomy can be measured in the
 mitochondrial function, the body weight and the basal oxygen consumption.
The operation of hemithyroidectomy (total thyroid lobectomy and isthmusectomy with
 preservation of the contralateral lobe) is indicated for patients with a unilateral thyroid
 mass that is causing compressive symptoms, cosmetic concern or to exclude thyroid carcinoma.

 The incidence and risk factors for development of hypothyroidism after hemithyroidectomy
 remain unclear. The reported rates of postoperative hypothyroidism vary from 5.0% to 41.9 %
 because of variable follow-up and definition of hypothyroidism (Wormald et al). There are no
 nationally nor universally accepted guidelines for the monitoring of thyroid function after
 hemithyroidectomy.

 Subclinical hypothyroidism is associated with an increased risk of coronary heart events and
 coronary heart mortality (Rodondi et al) and a high level of thyrotropin (within the
 laboratory reference range) has been related to an increased risk of fatal coronary heart
 disease (Asvold et al) Variation in thyroid function is seen between individuals also within
 the normal range. The individual variation in serum levels of thyroid hormones and
 thyrotropin between measurements in the same individual is relatively small compared with
 variations between individuals (Andersen et al). This implicates that around half of the
 laboratory reference range for thyrotropin is abnormal for a given individual. The fact that
 a thyrotropin value of an individual can be within the reference range but still represent an
 abnormal thyroid function in that given person has consequences for the monitoring of thyroid
 function after hemithyroidectomy. It implies that the postoperative thyroid function should
 be monitored by having the preoperative thyroid function in mind and that postoperative
 hypothyroidism should be understood in a broader term. After hemithyroidectomy a change in
 the individual unique set point that results in a lowered thyroid function can represent a
 condition that the investigators refer to as individual subclinical hypothyroidism.

 Weight gain following hemithyroidectomy for benign nodular goiter among patients that do not
 develop overt hypothyroidism is a frequent clinical observation. Body weight is influenced by
 many factors, there among thyroid function. Even small differences in thyroid function with
 s-thyrotropin variations within the normal laboratory range for patients on T4 substitution
 therapy are associated with differences in resting energy expenditure. A prolonged decrease
 in REE could lead to increased body weight (al-Adsani et al).

 Overweight and obesity are major threats to public health. The importance of lifestyle for
 weight gain is not to be doubted but other factors such as slight differences in thyroid
 function might be of importance in the risk of gaining weight as well (Knudsen et al).

 The mitochondria provide cellular energy by converting oxygen and nutrients into ATP by
 aerobe respiration and mitochondrial energy production is regulated by thyroid hormones
 (Weitzel et al). Subclinical hypothyroidism has previously been shown to affect mitochondrial
 function in mononuclear blood cells (Kvetny et al).

 The investigators hypothesize that after hemithyroidectomy some patients develop lowered
 thyroid function which results in a postoperative higher value of serum thyrotropin as a
 consequence of less negative feed-back on the pituitary gland. Weather the postoperative
 lowered thyroid function results in overt hypothyroidism (serum thyrotropin above the upper
 reference limit, lowered serum levels of free T3 and T4), subclinical (serum thyrotropin
 above the upper reference limit, free T3 and T4 within the reference range) or individual
 subclinical hypothyroidism (serum thyrotropin rises within the reference range, free T3 and
 T4 within the reference range) depends on the preoperative set point of thyroid function of
 the given patient but either condition represents a condition that is abnormal. The
 investigators hypothesize that a postoperative lowered thyroid function will affect
 mitochondrial function and result in weight gain.
Inclusion Criteria:

 -  Is going to undergo hemithyroidectomy for nontoxic goiter at the department of
 otorhinolaryngology at Slagelse Hospital, Denmark.

 -  BMI 20-40

 -  No past thyroid diseases

 -  No medication with influence on the pituitary-thyroid axis

 -  No hormone replacement therapy

 -  No childbirth or pregnancy within the last year

 -  Not currently breastfeeding

 Exclusion Criteria:

 -  Malignant goiter, diagnosed by histological examination of the resected tissue

 -  Pregnancy