Despite the description of low T3 syndrome above 40 years ago, its pathogenesis has not been completely understood. Various parameters have been considered to play role in this syndrome, including inhibitors of T3 or T4 binding to proteins, decreased deiodinase 1 (D1), and deiodinase 2 (D2) activities and increased deiodinase 3 (D3) activity, as well as are tumour necrosis factor α (TNFα), interleukin 6 (IL-6) [8]. In addition, one of the dilemmas is the significance of low T3 syndrome in critically ill patients. Some researchers demonstrated a protective function of that phenomenon [9], while others reported rather as either an adaptive process in the condition of reduced energy supplies or a maladaptive one, resulting in tissues impairment [10].
When discussing the low T3 syndromes, it should be mentioned that this phenomenon occurs immediately after operation due to stress [7]. Disturbances of thyroid function can be observed within the first hours after skin incision [8]. Furthermore, patients with low T3 level were older than those with normal T3 level and in case of critically ill patients, low T3 syndrome was much more frequently found in the non-survivors than in survivors; consequently, the case fatality rate (CFR) was much higher in the group of patients with low T3 level than in patients with normal T3 [11].
Our findings have confirmed reduction of FT3 values on 1st, 3rd, 5th day after surgery in both studied groups, though the FT3 values decreased below the reference range only in 3rd and 5th day after major surgery. Thus, our observations are in compliance with previous studies that proved the presence of low T3 syndrome in patients after minimally invasive laparoscopic cholecystectomy [7] and after major cardiopulmonary bypass surgery [12, 13]. Additionally, just as expected, patients with low T3 concentrations before surgery demonstrated postoperatively a more severe degree of low T3 syndrome [12].
The comparable results of thyroid function tests in two analyzed subgroups provide some evidence that the extent of abdominal surgery does not impact significantly on the thyroid condition. This part of our results is in agreement with prior study [14] in which surgical procedures were divided into minor, moderate and extensive surgery and - likewise in our study - on the 1st day after surgery serum FT3 levels decreased in all 3 groups, when compared to the baseline values. Serum FT4 levels did not change regardless of surgical procedure [14]. However, certain discrepancy exists between previous quoted results and our observations. In opposite to our findings, Murai et al. [14] demonstrated that serum TSH levels decreased significantly on 1st day after surgery in the groups of moderate and extensive surgery.
It is worth stressing that in the our study patients who underwent minor surgery, mainly palliative due to unresectable abdominal tumours, were in the worse general condition before operation than patients who underwent major surgery. In our opinion, this fact - together with surgery extent - influenced the thyroid hormone metabolism and resulted in the similar final thyroid condition in both subgroups. This suggestion stays in accordance with results of earlier study in which authors demonstrated that the abnormalities in thyroid hormone metabolism were more frequent in patients admitted for urgent surgery than in patients scheduled for elective surgery. Furthermore, half out of the patients who underwent urgent surgery, persisted with changes in thyroid function tests in the late postoperative period, whereas most of the patients submitted to elective surgery presented an improvement in their thyroid function in the same period of time [6]. These results could indicate that the low T3 syndrome rather reflects the seriousness of patient’s general condition than the impact of surgery.
Our further statistical analyses revealed lower mean FT3 and FT4 concentrations after surgery in pancreatic tumours patients when compared to liver tumours patients. It is tempting to speculate that novel finding could be explained by an increased proportion of free thyroid hormones after liver surgery, caused by lower thyroid hormone binding proteins concentrations (hypoproteinemia) [15, 16]. Another explanation might be based on an assumption that pancreatic surgery – generally - is a more serious procedure with more serious complications and lower free thyroid hormones levels are known to be a manifestation of particularly deep and serious metabolic disturbances.
Furthermore, it is worth mentioning that low T3 syndrome early after partial hepatectomy, characterized by increased activity of D3, associated with low serum and liver thyroid hormone levels, has been proved to have important role in the regenerating liver, in which a decrease in cellular T3 promotes an increase in proliferation [17]. The last cited report supports the hypothesis that low T3 syndrome is an adaptive process.
In order to make discussion on our results completed, we have to recall that although the extent of abdominal surgery does not impact significantly on the thyroid function, patients after pancreatic surgery are more likely to reveal lower FT4 levels.