Left-Shifted Relation Between Calcium and Parathyroid Hormone in Graves Disease. Maria Annerbo, Hella Hultin, Peter Stålberg, and Per Hellman

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1 ORIGINAL Endocrine ARTICLE Research Left-Shifted Relation Between Calcium and Parathyroid Hormone in Graves Disease Maria Annerbo, Hella Hultin, Peter Stålberg, and Per Hellman Department of Surgical Sciences (H.H., P.S., P.H.), Uppsala University, SE Uppsala, Sweden; and Department of Surgery (M.A.), County Hospital, SE Falun, Sweden Background: Patients with Graves disease (GD) have disturbances in calcium regulation with manifestations such as postoperative hypocalcemia. We have investigated the thyroid as well as the parathyroid function in detail. Materials and Method: A series of patients undergoing total thyroidectomy for GD (n 56) or multinodular goiter (MNG; n 50) were scrutinized for postoperative hypocalcemia and a need for calcium and/or vitamin D substitution. A citrate-calcium (CiCa) clamp was used in 14 patients and 21 controls to quantify the secretion of PTH in relation to the ionized plasma calcium level. The set point, equal to the plasma-ionized calcium concentration at which 50% of the maximal secretion of PTH is inhibited, as well as other CiCa-related parameters were calculated. Results: Hypocalcemia was present in 48% of GD and 41.2% of patients with MNG postoperatively. Patients with GD had lower calcium levels, 18% had serum Ca less than 2.00 mmol/l compared with 4.0% in the MNG group (P.02). A higher degree of GD patients were given parenteral calcium substitution during the hospital stay (3.6% vs 0 %) and oral calcium substitution at discharge (48% vs 10%), although they had normal vitamin D3 levels. The GD group showed a significantly leftshifted set point compared with the normal group on the CiCa clamp, 1.16 mmol/l vs 1.20 mmol/l (P.001) as well as an increased PTH release to hypocalcemic stimulus. GD patients also show an association between degree of subclinical toxicosis at time of surgery and risk for developing postoperative hypocalcemia. Conclusion: Patients with GD demonstrate dysregulation of the calcium homeostasis by several parameters. GD patients have lower postoperative serum calcium compared with patients with MNG, lower calcium/pth set point, and a significantly increased release of PTH to hypocalcemic stimulus compared with controls. The CiCa clamp response in GD patients with normal 25-hydroxyvitamin D3 levels mimics that of obese patients in which vitamin D insufficiency has been proposed as an underlying cause. (J Clin Endocrinol Metab 99: , 2014) The increased metabolism in Graves disease (GD) may in certain cases also involve increased metabolism in the skeleton with a high bone turnover (1). This has been interpreted as bone hunger, usually revealed in the postoperative period. Indeed, some authors have noted that GD patients need more postoperative calcium after total thyroidectomy than does multinodular goiter (MNG) patients (2 4). Because levels of PTH are normal in this situation, a relative hypoparathyroidism and not surgical ISSN Print X ISSN Online Printed in U.S.A. Copyright 2014 by the Endocrine Society Received June 11, Accepted November 1, First Published Online November 18, 2013 trauma to the parathyroid glands per se may cause this (5). Nevertheless, it is still under debate whether this hypocalcemia is due to less skilled surgeons (6, 7), hungry bone syndrome-related to thyrotoxicosis (8), low vitamin D levels (9), increased thyroidal blood flow leading to more easily harmed parathyroid glands, or some other unknown immunological mechanisms. In our previous series of patients operated on for GD, we have noted a ratio of patients with hypocalcemia (serum calcium 2.00 Abbreviations: CaR, calcium receptor; CiCa, citrate-calcium; GD, Graves disease; GO, Graves ophthalmopathy; MNG, multinodular goiter; phpt, primary hyperparathyroidism; PTHmax, maximal PTH secretion; PTHmin, minimal PTH secretion; s-ca, serum calcium; TRAb, TSH receptor antibody. doi: /jc J Clin Endocrinol Metab, February 2014, 99(2): jcem.endojournals.org 545

2 546 Annerbo et al Left-Shifted Calcium Set Point in Graves Disease J Clin Endocrinol Metab, February 2014, 99(2): mmol/l) of 21.8% on day 1 and 7% on day 2, whom at discharge were given calcium and vitamin D supplementation in 33.2% and 9.5%, respectively (10). Other studies have noted no difference between postoperative hypocalcemia in GD and MNG (3, 11, 12). To expand our knowledge of the calcium homeostasis in patients with GD and to characterize changes in the immediate postoperative period, relate to preoperative thyroid functional status, and investigate the role of the parathyroid glands, we have studied 56 patients operated with total thyroidectomy for GD. In addition, 14 cases were thoroughly investigated by performing preoperative citrate-calcium (CiCa) clamp, allowing detailed analysis of the parathyroid function. Materials and Methods Of all patients who were planned for total thyroidectomy (TT) between March 2009 and April 2012 at the University Hospital in Uppsala (n 78) or the County Hospital in Falun (n 37), 56 normal-weighted patients volunteered to participate, 52 females and four men, mean age 41 years (range 9 67 y). They were investigated to scrutinize the calcium homeostasis before the operation and in the immediate postoperative period. GD was diagnosed by using TSH receptor antibody (TRAb) levels and measurements of TSH, T 4, and T 3. The patients were operated on by two senior surgeons in Falun and three senior surgeons in Uppsala. All but one of the GD patients were pretreated with antithyroid drugs (carbimazole or tiamazole) for an average of 21 months (3 48 mo). As a general rule, we have used the blockand-replace method in almost all cases, which in general means mg carbimazole two times daily (or tiamazole 100 mg two times daily), and after 4 weeks the addition of a daily dose of at least 50 g levothyroxine. This treatment will protect the patients from effects caused by TSH elevation, but as TSH release is inhibited, it will also hide true euthyroidism. In attempts of further clarification, we have divided the patients into three groups according to their preoperative thyroid status according to the TSH level as the only, but still somewhat unreliable, measure of eu- or hyperthyroidism preoperatively: 1) laboratory euthyroid patients (n 15) with TSH greater than 0.4 in more than 3 months before surgery; 2) a laboratory subthyrotoxic group (n 22) with preoperative TSH ; and 3) a presumed thyrotoxic or block-and-replace-suppressed group (n 14) with TSH less than As a result of antithyroid treatment, all were clinically euthyroid at the time of surgery. -Blockers were used sporadically to handle the symptoms. Seven patients were prescribed nonselective -receptor blocker, propranolol. The majority, five of seven, was taking their medication on demand sporadically for 2 weeks. Two patients with more aggressive disease did take propranolol 40 mg regularly two to three times a day for 3 4 months before surgery. Main indications for surgical treatment were as follows: recurrent disease, 42.8%; aggressive disease with difficulties to maintain medication, 44.3%; Graves ophthalmopathy (GO), 25%. More severe GO, defined as intense pain, eyelid retraction, and/or sight impairment was seen in eight patients (six were treated with corticosteroids). The proportion of large goiter (defined as weight 40 g) was 10.7% (13). The average thyroid weight was 35.5 g (range g). In median, three parathyroid glands were identified at surgery, and in 14 of 56 operations, a reimplantation of a normal-looking parathyroid gland was performed. Blood samples were collected preoperatively as well as on days 1 5 postoperatively and at follow-up 1 and 6 months postoperatively. Among the 56 GD patients, 14 patients [13 females, mean age 39.9 y (range y)] agreed to participate in a more detailed investigation of their calcium metabolism, by undergoing a CiCa clamp. All but one were investigated in an average of 5 weeks (1 14 wk) before surgery, and no difference was seen in set point or maximum PTH release between these and the single patient who was treated with carbimazole 57 weeks between the CiCa clamp and the operation. All but one patient were treated with antithyroid drugs for a mean of 18 months (range 4 48 mo) and had similar calcium characteristics as the whole group pre- and postoperatively (Table 1). GO of various degree was seen in 9 of 14 (64%) patients, of which three (21%) had more severe GO and were under treatment with corticosteroids. The CiCa clamp findings in the GD patients were compared with 21 healthy individuals [mean age 51.3 y (range y)], in which some previously have been described from our institution (14). Recent healthy controls demonstrated similar calcium and PTH values and response during CiCa clamp as previously characterized ones. Moreover, our levels and results from a CiCa clamp in our healthy controls were similar to and hereby confirmed when compared with cohorts presented in the literature (15). From the same institution, data from a cohort of 15 patients with primary hyperparathyroidism [phpt; mean age 67.9 y (range y)] and another of obese individuals (n 11, mean body mass index kg/m 2, mean age 47 9 y; eight females) were used as comparison (14) (Figure 1 and Supplemental Figure 1, published on The Endocrine Society s Journals Online web site at From the same time period, data were collected from MNG patients operated with total thyroidectomy at Falun County Hospital (n 50). The mean age in this group was 64.4 years Table 1. Calcium Characteristics in Patients With GD GD (n 56) Cica (n 14) Age, y ,1 10,1 Preop ion Ca Preop corr s-ca Preop ipth Preop 25-hydroxyvitamin D Day 1 ion Ca Day 1 corr S-Ca Day 1 ipth Month ion Ca Month corr s-ca Month ipth Month 25-hydroxyvitamin D Abbreviations: corr, albumin-corrected values of total s-ca; Day 1, first postoperative day; Ion Ca, ionized calcium; ipth, intact PTH; Preop, values obtained preoperatively, as close to surgery as possible. Calcium was measured in millimoles per liter, PTH in picomoles per liter, and 25-hydroxyvitamin D3 in nanomoles per liter. No significant differences between groups are present.

3 doi: /jc jcem.endojournals.org 547 Figure 1. Graphs of CiCa clamping of normal healthy individuals, patients with Graves disease, and obese individuals (15). Arrows indicate set point in Graves patients as well as normal individuals. Interposition line is drawn using fifth-degree polynomial curve fitting and spine interpolation with a piecewise polynomial function. (range y). They were all normocalcemic and euthyroid with normal levels of T 4 and T 3, although 15 of 50 had a subclinical hyperthyroidism with TSH mu/l. Mean thyroid weight was 146 g (range g). No one was treated with either antithyroid drugs or propranolol. The number of observed parathyroid glands was the same as in the GD cohort. Biochemistry Basal serum or plasma values for albumin, calcium, creatinine, intact PTH, phosphate, TSH, T 4, and T 3 were measured at the clinical chemistry laboratories in Uppsala or Falun, respectively, whereas anti-trabs and 25-hydroxyvitamin D solely were determined at the clinical chemistry laboratory at the University Hospital in Uppsala. Serum albumin was determined by spectrophotometry using bromine cresol green (normal range g/l). Total serum calcium (s-ca) was measured spectrophotometrically using a compleximetric method with orthocresolphthalein (normal range mmol/l) and was adjusted to the serum albumin level by using the following formula: total s-ca [0.019 (43 serum albumin)]. Hypocalcemia was defined as an albumin-corrected serum calcium level of less than 2.15 mmol/l and severe hypocalcemia as serum levels below 2.00 mmol/l. Serum creatinine was measured by spectrophotometry using Jaffe s reaction (normal range mol/l). TSH, T 4, and T 3 were analyzed on Cobas Immuno602 (Roche) in Uppsala or the Architect ci8200 (Abbott Laboratories) in Falun. A chemiluminescent method (chemiluminescence immunoassay) was used to measure both intact plasma PTH (normal reference range pmol/l) Liasion 1 84 PTH and 25- hydroxyvitamin D, Liasion 25-hydroxyvitamin D assay (Diasorin). The 25-hydroxyvitamin-D values were compared with a reference population analyzed at the same laboratory and with the same method (16). The 25-hydroxyvitamin D values were analyzed separately according to seasonal variations (summer values defined as samples collected during May-October, winter values collected November-April). The TRAb levels were determined by an ELISA with human monoclonal antibody (HuMab-TRAb; reference range 0.6 U/L; RSR Ltd). CiCa clamp The CiCa clamp is a method measuring in vivo function of the parathyroid glands and their sensing of external calcium. The method has been proven reproductive and reliable with minimal interindividual variations (15, 17). We have been using this method at our institution for more than 18 years. During 50 minutes a body weight-related citrate infusion is infused. When hypocalcemia is established, calcium is infused during 60 minutes to create hypercalcemia. Intact plasma PTH and ionized plasma calcium are collected at predefined time intervals during the procedure. The set point of calcium was calculated, as described by Bas et al (18). The set point is equal to the plasma-ionized calcium concentration at which 50% of the maximal secretion of PTH is inhibited, measured as the plasma-ionized calcium concentration at the midrange of the PTH maximum-pth minimum curve. We also determined basal PTH secretion (before infusions started), maximal PTH secretion (PTHmax), minimal PTH secretion (PTHmin), and the ratio of basal PTH to maximum PTH. Furthermore, we measured the ionized calcium concentration at PTHmax, defined as the ionized calcium concentration when maximum PTH is reached and no further reduction in ionized calcium led to any increase in PTH. In addition, we measured the ionized calcium concentration at minimum PTH, defined as the ionized calcium concentration at which PTH reached minimum PTH, and no further increase in ionized calcium led to any further reductions in PTH. Statistics IBM SPSS Statistics version 20.0 was used for calculations and visualization. A Student s unpaired t test and a Mann-Whitney U test were used for the characterization of statistical difference between two variables and a Pearson s test for evaluating correlations. P.05 was considered as significant. Graphic visualization was performed by both using fifth-degree polynomial curve fitting and spine interpolation using a piecewise polynomial function. Ethics The study was approved by the local ethics committee (reference number 2008/275). All patients signed a written informed consent before inclusion in the study.

4 548 Annerbo et al Left-Shifted Calcium Set Point in Graves Disease J Clin Endocrinol Metab, February 2014, 99(2): Results The rate of hypocalcemia, defined as albumin-corrected total s-ca less than 2.15 mmol/l, was 48% on postoperative day 1 in the GD patients and 41.2% in the MNG patients. Patients with GD had a higher rate of severe hypocalcemia ( 2.00 mmol/l) on postoperative day 1 (10 of 56; 17.9%), compared with those with MNG (2 of 50; 4.0%; P.02). In the MNG group, the patients with subclinical hyperthyroidism demonstrated a lower s-ca level at the first postoperative day, mmol/l, compared with those with TSH within normal range mie/l (P.029). Twelve of the 56 GD patients showed a low intact PTH ( 0.9 pmol/l), on postoperative day 1, indicating disturbance of parathyroid function. All of these had normalized ppth after 1 month. Ten of these 12 patients still needed calcium and/or vitamin D supplementation at 1 month and 5 of 12 patients at 6 months. Sixteen patients were hypocalcemic, although they had normal PTH levels, and 13 of these had normalized their calcium levels without ongoing substitution at 1 month, whereas the remaining three required medication also at 6 months. Altogether at 6 months, five patients with early postoperative low but later normalized ppth and three with early normal ppth required calcium and vitamin D supplementation at 6 months, indicating a postoperative ongoing disturbance in calcium homeostasis in 8 of 56 patients (14.3%). The GD patients needed more calcium and vitamin D substitution at discharge (46.4% vs 9.8%, P.001, and 12.5% vs 2%) than the MNG group. Preoperative thyroid function as described in the three groups designed according to the preoperative TSH level demonstrated no significant differences between all three groups, but when comparing TSH greater than 0.4 mie/l with TSH less than 0.4 mie/l, those with lower TSH had a significantly (P.047) higher risk for hypocalcemia on day 1 than the other patients. Moreover, the preoperative T 3 value, but not T 4, correlated significantly to the s-ca value at day 1 after surgery (P.028). The Scandinavian Registry for Thyroid and Parathyroid Surgery was scrutinized, and after more than 2500 total thyroidectomies in Sweden, 30% received an oral calcium dose at discharge after surgery and 13% oral vitamin D. At 6 months these numbers were reduced to 15% and 9%, respectively. Citrate-calcium The GD patients had a significantly left-shifted Ca- PTH relation curve compared with the normal-weight control group, visualized as a set point at 1.16 mmol/l vs 1.20 mmol/l (P.001, Mann-Whitney) as well as an increased response in release of PTH to hypocalcemic stimulus (PTHmax pmol/l in the CiCa group vs pmol/l in normal weight controls; P.001; Tables 2 and 3). The values were similar to those obtained in obese individuals (14), in which the set point was even lower than in the GD patients (Tables 2 and 3). Those patients who became postoperatively hypocalcemic (s- Ca 2.15 mmol/l, n 5) had higher PTH levels at baseline (8.5 pmol/l vs 4.9 pmol/l in the normal group, n 7; P.03). They also showed an augmented reaction to hypocalcemic stimulus (PTHmax 53.8 pmol/l vs 28.9 pmol/l; P.03). There were no differences in vitamin D levels between these groups (58.7 nmol/l vs 53.8 nmol/l). 25-Hydroxyvitamin D The 25-hydroxyvitamin D levels in patients with GD was a mean 55.6 nmol/l (range nmol/l), which is equal to the normal population living in the same area (16). The group that suffered from either hypocalcemia Table 2. Parameters From the CiCa Clamp in Patients With GD, phpt, and Obese and Normal-Weight Individuals GD (n 14) NW (n 21) phpt (n 15) Obese (n 11) Basal PTH a PTHmin a PTHmax a PTHb/m SP a Ca at PTHmax a b Ca at PTHmin a Abbreviations: Ca at PTHmax, ionized calcium concentration at PTHmax, defined as the ionized calcium concentration when maximum PTH is reached; Ca at PTHmin, ionized calcium concentration at minimum PTH, defined as the ionized calcium concentration at which PTH reached minimum PTH; NW, normal weight healthy controls; PTHb/m, ratio of basal PTH to maximum PTH; SP, set point between calcium and PTH. PTH was measured in picomoles per liter and calcium in millimoles per liter. a Indicates significant differences between GD patients and controls. As a comparison, results of a previously described cohort with phpt is described (all parameters are significant toward healthy normal weight controls as well as GD patients, referent). b Indicates significant differences between GD patients and obese individuals.

5 doi: /jc jcem.endojournals.org 549 Table 3. Plasma Ionized Calcium (Millimoles per Liter, p-ca) and Plasma Intact PTH (Picomoles per Liter, p-ipth) Within the Different Groups of Patients (GD, n 14; phpt, n 15; Obese, n 11) and Healthy Controls (n 21) Before Citrate Calcium 10 Min 5 Min 10 Min 20 Min 40 Min 50 Min 80 Min 95 Min 115 Min Graves p-ca 1.19 a 1.13 a 1.08 a 1.04 a a p-ipth 6.4 a 33.5 a 36 a 23.1 a a Control p-ca p-ipth phpt p-ca 1.39 a 1.29 a 1.26 a 1.15 a 1.09 a 1.06 a 1.16 a 1.55 a 1.59 a p-ipth 9.8 a 19.9 a 27.6 a 21.0 a 17.8 a 16.5 a 9.5 a 8.5 a 8.1 a Obese p-ca 1.17 a 1.11 a 1.05 a 1.00 a 0.95 a a 1.33 a 1.37 a p-ipth 7.3 a 30.6 a 40.7 a 25.3 a 17.0 a 14.9 a 2.3 a Time labels indicate when sampling was performed during CiCa clamp. From 0 50 minutes, the subjects received citrate infusion (citrate) and thereafter calcium infusion. Values are presented as mean only (without SD). a Significant (P.01) difference compared with healthy controls. [ 2.15 mmol/l; vitamin D in mean 58 (range nmol/l)] or severe hypocalcemia [ 2.00 mmol/l; vitamin D in mean 45.9 (range nmol/l)] showed no significant differences in vitamin D levels compared with the normocalcemic group [vitamin D: 52.4 nmol/l (range nmol/l)]. In patients with low postoperative ppth values, there were no differences in vitamin D levels [mean 63.2 nmol/l (range nmol/l)] compared with patients with ppth in the normal range [mean 54 nmol/l; range nmol/l)]. There were seasonal variations in the vitamin D levels taken in the summer (64.6 nmol/l) compared with the winter values (48.25 nmol/l; P.03). Discussion Postoperative hypocalcemia in patients with GD is a wellknown clinical problem. Indeed, some recent reports have claimed the lack of this problem, but the present study is in agreement with both previous and larger surveys (3, 19, 20) and recently published data (21 23). Thus, we have demonstrated that patients with GD are at higher risk for developing hypocalcemia postoperatively despite being preoperatively medically treated to euthyroidism. The 25- hydroxyvitamin D levels did not differ from the normal population, which in earlier studies has been shown to be a strong contributor to the postoperative hypocalcemia (9). However, in the present study, the patients with low 25-hydroxyvitamin D levels did not demonstrate a more extended hypocalcemic response to surgery than the ones with normal vitamin D levels. We also conclude that GD patients reach significantly lower serum calcium levels postoperatively and are at higher risk for a need of calcium and vitamin D supplementation at discharge than patients with MNG undergoing the same operation. Moreover, the risk for long-standing need of supplementation is high, also with normal ppth values. Presumably other factors than merely surgical trauma to the parathyroid glands may underlie this difference. The present study investigates the hypocalcemic response to surgery but with a special focus on the parathyroid function. In the search for possible explanations, high T 3 was found to eventually indicate postoperative hypocalcemia (P.028), and patients with TSH less than 0.4 mie/l had a higher risk for postoperative hypocalcemia than those with TSH greater than 0.4 mie/l (P.047). The CiCa clamp results further contribute to the hypothesis of a disturbed calcium homeostasis due to disturbed parathyroid function in GD. Results from earlier studies in animals and obese individuals have indicated that low levels of vitamin D may be associated with a left-shifted calcium-pth relationship (14). The obese cohort investigated at our institution are vitamin D deficient with values of 25-hydroxyvitamin D at ,5 nmol/l vs nmol/l in the GD group, the latter being similar to the normal population (16). In the present study of GD patients, 25-hydroxyvitamin D is analyzed at the same laboratory with the same method (chemiluminescence immunoassay; Liasion). The CiCa patients had similar vitamin D values as the whole group, although 7 of 10 samples among the CiCa patients were collected during winter. Although the group of patients with severe postoperative hypocalcemia had lower vitamin D levels on average, this may also be explained by seasonal variations. Therefore, in the current cohort of GD patients, we could not explain the left-shifted set point by low vitamin D levels.

6 550 Annerbo et al Left-Shifted Calcium Set Point in Graves Disease J Clin Endocrinol Metab, February 2014, 99(2): We therefore conclude that vitamin D insufficiency is not a major cause for the calcium disturbance as measured by CiCa clamp in GD. Another finding in the CiCa clamps was the marked response in PTH secretion to a hypocalcemic stimulus, being similar to the reaction seen in obese individuals (14). This marked response is even more prominent in the group of patients who will develop postoperative hypocalcemia. Purely speculatively, this may be due to high expression of the calcium receptor (CaR) on the surface of parathyroid cells or by expression of certain polymorphic variants of CaR. The latter has been shown to influence the serum calcium level in normal individuals (24). Another possibility is an increased store of secretory granules containing PTH, which is released upon the hypocalcemic stimulus. Whether any of these possible situations explain the response seen in GD is beyond the scope of the current study. The issue of postoperative hypocalcemia has recently been discussed in a study describing the situation seen in the Scandinavian Thyroid-Parathyroid Registry (12). The results from 128 patients indicate that GD patients have more pronounced symptoms of hypocalcemia than other patient groups after the same operation (total thyroidectomy), despite equal levels of s-ca. This is somewhat confusing because our material partly was registered in the same registry. However, the levels of serum and ionized calcium in the registry is up to 50% of a mere calculation using a mathematic formula (ionized calcium s-ca/2), which may raise doubts regarding the scientific value of the postoperative calcium levels in that study. In addition, patients with subclinical hyperthyroidism may be part of the group of MNG patients, possibly creating bias in the analysis of postoperative calcium levels. In our series, patients with subclinical hyperthyroidism had lower postoperative s-ca levels than the euthyroid MNG patients. In the present study, all patients with GD demonstrated ppth within normal range after 6 months, but 8 of 56 (14.3%) still needed calcium or vitamin D supplementation. Moreover, the registry demonstrates that oral calcium was given in 30% and vitamin D at 13% at discharge, which is in the similar range as in our investigated cohort. One limitation of the present study is the low number of patients studied by CiCa clamp. However, this smaller group of GD patients show no difference regarding the degree of GD, the grade of postoperative hypocalcaemia, and the ppth levels toward the remaining patients. The lack of total inclusion of patients may also affect the results, although the cohort of 56 GD patients correlates well with our earlier retrospective material concerning operative indications, GD activity, complication rates, and percentage of postoperative hypocalcemia on day 1. The advantages of the study include the prospective design and the close follow-up of data. Our results implicate that patients with GD have a disturbed calcium metabolism, in the present study visualized preoperatively by the CiCa clamp and postoperatively by the increased incidence of severe hypocalcemia. Reasons for this disturbance remain unclear, although most likely involves the parathyroid gland function themselves, but signs of remaining biochemical hyperthyroidism, although treated to clinical euthyroidism, may also contribute. Possible explanations for dysregulated parathyroid glands are more or less unknown, but autoantibodies directed toward the parathyroid cells or polymorphism in CaR may be present. Acknowledgments We greatly acknowledge the skillful performance of the CiCa clamps by Erika Aretis. Address all correspondence and requests for reprints to: Per Hellman, MD, Department of Surgery, University Hospital, SE Uppsala, Sweden. per.hellman@me.com. The work was funded by the Regional Research Council, in the Region of Uppsala-Örebro, as well as by Bergholm s and Eriksson s foundations. Disclosure Summary: The authors have nothing to disclose. References 1. Mosekilde L, Eriksen EF, Charles P. Effects of thyroid hormones on bone and mineral metabolism. Endocrinol Metab Clin North Am. 1990;19: Thomusch O, Machens A, Sekulla C, et al. Multivariate analysis of risk factors for postoperative complications in benign goiter surgery: prospective multicenter study in Germany. 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