Risk factors for developing hyponatremia in thyroid cancer patients undergoing radioactive iodine therapy

Effect of preparation method for radioactive iodine therapy on serum electrolytes

PURPOSE

Thyroid hormone withdrawal (THW) in preparation for radioactive iodine therapy (RIT) may lead to hyponatremia and hyperkalemia because hypothyroidism reduces the glomerular filtration rate. Using recombinant human thyrotropin (rhTSH) may avoid these changes; however, these two preparation methods have not been compared in the literature. The purpose of this study was to reveal whether THW and rhTSH as preparation methods for RIT affect serum electrolytes differently. We also evaluated clinical factors influencing the onset of hyponatremia and hyperkalemia during RIT.

MATERIALS AND METHODS

From April 2005 to December 2020, we analyzed 278 patients with thyroid cancer who received RIT. The patients were classified into two groups based on the preparation method, and renal function and serum electrolytes were compared between the groups. We also evaluated clinical factors that may affect overt hyponatremia (serum sodium level < 134 mmol/L) and hyperkalemia (serum potassium level ≥ 5.0 mmol/L).

RESULTS

Serum sodium and chloride levels in the THW group were significantly lower than those in the rhTSH group (p < 0.001 and p = 0.002, respectively). In contrast, the serum potassium level in the THW group was significantly higher than that in the rhTSH group (p = 0.008). As for clinical factors that may influence hyponatremia, age and estimated glomerular filtration rate (eGFR) were significantly associated with serum sodium level in the univariate analysis (p = 0.033 and p = 0.006, respectively). In the multivariate analysis, only age was significantly associated with serum sodium level (p = 0.030). Regarding hyperkalemia, distant metastases, the preparation method and eGFR were significantly associated with the serum potassium level in the univariate analysis (p = 0.005, p = 0.005 and p = 0.001, respectively). In the multivariate analysis, only eGFR was significantly associated with hyperkalemia (p = 0.019).

CONCLUSION

THW and rhTSH affect serum sodium and potassium levels differently. Renal function may be risk factors for hyperkalemia, whereas older age may be a risk factor for hyponatremia.

Impact of low iodine diets on ablation success in differentiated thyroid cancer: A mixed-methods systematic review and meta-analysis

BACKGROUND

Debate remains regarding whether to recommend a low iodine diet (LID) before radioactive-iodine treatment and its duration and stringency. This mixed-methods review aimed to determine if iodine status affects treatment success, the most effective diet to reduce iodine status, and how LID impacts wellbeing.

METHODS

Five electronic databases were searched until February 2021. An effectiveness synthesis (quantitative studies) and views synthesis (qualitative, survey, and experience-based evidence) were conducted individually and then integrated. Quality assessment was undertaken.

RESULTS

Fifty-six quantitative and three qualitative studies were identified. There was greater ablation success for those with an iodine status of &lt;50 mcg/L (or mcg/gCr) compared with ≥250 (odds ratio [OR] = 2.63, 95% confidence interval [CI], 1.18-5.86, n = 283, GRADE certainty of evidence very low). One study compared &lt;50 mcg/L (or mcg/gCr) to 100-199 and showed similar rates of ablation success (OR = 1.59, 95% CI, 0.48-6.15, n = 113; moderate risk of bias). People following a stricter LID before ablation had similar rates of success to a less-strict diet (OR = 0.67, 95% CI, 0.26-1.73, n = 256, GRADE certainty of evidence very low). A stricter LID reduced iodine status more than a less strict (SMD = -0.40, 95% CI, -0.56 to -0.24, n = 816), and reduction was seen after 1 and 2 weeks. The main challenges were a negative impact on psychological health, over restriction, confusion, and difficulty for sub-groups.

CONCLUSIONS

Although a LID of 1-2 weeks reduces iodine status, it remains unclear whether iodine status affects treatment success as only a few low-quality studies have examined this. LIDs are challenging for patients. Higher-quality studies are needed to confirm whether a LID is necessary.

The utility of low-iodine diet in preparation for thyroid cancer therapy with radioactive iodine—A cohort study

Objective: A low-iodine diet (LID) of <50μ iodine/day is recommended as preparation for radioactive iodine (RAI) therapy in patients with differentiated thyroid cancer (DTC). The 24-h urinary iodine excretion (UIE) is utilized to evaluate the iodine-depleted status. The aim of this study was to test the association between UIE and progression-free survival (PFS).

Patients and methods: In total, 70 patients with intermediate- or high-risk DTC, post-total thyroidectomy, adhered to 2 weeks of LID and had UIE measured before RAI therapy. A Cox regression model was performed to study the contribution of UIE to PFS.

Results: The study group consisted of 68% (48/70) of women, aged 41.5 [IQR 31.0, 54.0] years, with tumor size 2.8 [IQR 1.8–4.5] cm, and presence of distant metastases in 22.9% (16/70) of patients. Patients were treated with 1–5 RAI dosages with the median cumulative activity of 150 [IQR 102–314] mCi (5.5 [IQR 3.8–11.6] GBq). During the follow-up of 3.7 [IQR 1.5–6.5] years, 21.4% (15/70) of patients had disease progression. The risk of progression was significantly higher in patients with UIE ≥200 µg/day at the time of RAI administration than in those with UIE <200 µg/day (HR 3.35, 95% CI 1.09–10.34, and p = 0.02). However, the multivariate Cox proportional hazards regression analysis adjusted for age, tumor size, and presence of distant metastases suggested that only distant metastases were independently significantly associated with the risk of progression (HR 5.80 (1.17–28.67), p = 0.03).

Conclusions: Although UIE ≥200 µg/day might be associated with worse PFS in RAI-treated DTC patients, the presence of distant metastases is a strong independent predictor of progression. Less stringent LID might be sufficient to achieve a UIE of <200 µg/day.

Analysis of the incidence and influencing factors of hyponatremia before 131I treatment of differentiated thyroid carcinoma

BACKGROUND

Hyponatremia is a common clinical electrolyte disorder. However, the association between hyponatremia and acute hypothyroidism is unclear. Acute hypothyroidism is usually seen in patients who undergo preparation for radioactive iodine therapy.

AIM

To analyze the incidence and influencing factors of hyponatremia in a condition of iatrogenic acute hypothyroidism in patients with differentiated thyroid cancer (DTC) before ¹³¹I treatment.

METHODS

The study group consisted of 903 DTC patients who received ¹³¹I treatment. The clinical data before and after surgery, as well as on the day of ¹³¹I treatment were analyzed. According to the blood sodium level before ¹³¹I treatment, patients were divided into the non-hyponatremia group and hyponatremia group. Correlations between serum sodium levels before ¹³¹I treatment and baseline data were analyzed. Univariate analysis and binary logistic regression were performed to identify the influencing factors of hyponatremia.

RESULTS

A total of 903 patients with DTC, including 283 (31.3%) males and 620 (68.7%) females, with an average age of 43.8 ± 12.7 years, were included in this study. The serum sodium levels before surgery and ¹³¹I treatment were 141.3 ± 2.3 and 140.5 ± 2.1 mmol/L, respectively (P = 0.001). However, the serum sodium levels in males and females before ¹³¹I treatment were lower than those before surgery. Patients aged more than 60 years and less than 60 years also showed decreased serum sodium levels before ¹³¹I treatment. In addition, the estimated glomerular filtration rate (eGFR) in males and females decreased before ¹³¹I treatment compared with those before surgery (P = 0.001). Moreover, eGFR in patients over 60 years and under 60 years decreased before ¹³¹I treatment, when compared with that before surgery. There were no significant differences in serum potassium, calcium, albumin, hemoglobin, and blood glucose in patients before surgery and ¹³¹I treatment (P > 0.05). Among the 903 patients, 23 (2.5%) were diagnosed with hyponatremia before ¹³¹I treatment, including 21 cases (91.3%) of mild hyponatremia and 2 cases (8.7%) of moderate hyponatremia. Clinical data showed that patients with mild hyponatremia had no specific clinical manifestations, while moderate hyponatremia cases were mainly characterized by fatigue and dizziness, which were similar to neurological symptoms caused by hypothyroidism and were difficult to distinguish. Correlation analysis showed a correlation between serum sodium before ¹³¹I treatment and the preoperative level (r = 0.395, P = 0.001). There was no significant correlation between blood sodium and thyroid-stimulating hormone (TSH) levels and urine iodine before ¹³¹I treatment (r = 0.045, P = 0.174; r = 0.013, P = 0.697). Univariate analysis showed that there were significant differences in age, sex, history of diuretic use, distant metastasis, preoperative blood sodium, blood urea nitrogen (BUN), eGFR, TSH and urinary iodine between the two groups (all P < 0.05). Logistic regression analysis showed that factors such as history of diuretic use, distant metastases, preoperative sodium and BUN were all influencing factors of hyponatremia. The Hosmer and Lemeshow test (c2 = 2.841, P = 0.944) suggested a high fit of the model. Omnibus tests of model coefficients indicated the overall significance of the model in this fitted model (P < 0.05). Preoperative serum sodium was a significant factor associated with pre-¹³¹I therapy hyponatremia (OR = 0.763; 95%CI: 0.627-0.928; P = 0.007).

CONCLUSION

The incidence of hyponatremia induced by ¹³¹I treatment preparation was not high. Preparation for radioactive iodine therapy was not a risk factor for the development of hyponatremia in thyroid cancer patients.

Endocrinopathy-induced euvolemic hyponatremia

Euvolemic hyponatremia results from either the syndrome of inappropriate antidiuretic hormone secretion (SIADH), hypothyroidism, or adrenal insufficiency. Furthermore, the criteria for diagnosis of SIADH entail the exclusion of hypothyroidism and hypoadrenalism. We aim to assess the yield of euvolemic hyponatremia workup focusing on underlying endocrinopathies in a real-world setting. A single-center retrospective study includes all patients diagnosed with euvolemic hyponatremia in a tertiary hospital between 1.1.2007 and 1.1.2013. Demographic, clinical, and laboratory data were collected from medical charts. Euvolemic hyponatremia was detected in 564 patients. Thyroid function was tested in 69% (391/564) and adrenal function was assessed in 29% (164/564) of cases. Endocrinopathy-induced euvolemic hyponatremia was diagnosed in nine (1.6%) patients: three patients were diagnosed with hypothyroidism-induced hyponatremia, three with adrenal insufficiency as an underlying cause, and three with central hypothyroidism and central hypoadrenalism. All nine had medical history and symptoms suggestive of endocrine deficiencies other than the hyponatremia, which resolved within 1-3 days after administration of hormone replacement therapy. Yield of performed workup for hypothyroidism and hypoadrenalism in euvolemic hyponatremia was low. However, in this real-world study, only a limited number of patients underwent a full ascertainment of hypoadrenalism and hypothyroidism, which was diagnosed only in patients with additional findings supportive of these endocrinopathies; a higher rate of undiagnosed endocrinopathies cannot be ruled out. As both hypoadrenalism and hypothyroidism are easily treatable, potentially life-threatening conditions, there are insufficient data to change current recommendation for their universal evaluation in patients with euvolemic hyponatremia.

Preparation for radioactive iodine therapy is not a risk factor for the development of hyponatremia in thyroid cancer patients

The aim of this study was to evaluate whether the preparation for radioactive iodine (RAI) therapy by thyroid hormone withdrawal (THW) or a low-iodine diet (LID) can be risk factors for the development of hyponatremia in patients with differentiated thyroid cancer after thyroidectomy.We retrospectively reviewed the medical records and laboratory findings of 326 patients who underwent preparation for RAI therapy after thyroidectomy from 2012 to 2014. Demographic and clinical variables including the method of thyrotropin stimulation and duration of LID were assessed. Serum sodium was measured twice, before operation and before RAI therapy.Hyponatremia was detected in only 3 patients (0.9%) before operation, but in 15 patients (4.6%) before RAI therapy. None of the patients had severe hyponatremia after preparation for RAI therapy. Pre-RAI therapy serum sodium was correlated with the method of thyrotropin stimulation (TWH vs recombinant human thyroid stimulating hormone, P = 0.014) and duration of LID (r = -0.131, P = 0.018); however, the preparation of RAI therapy, THW and LID, did not affect the development of hyponatremia in logistic regression analysis. Preoperative serum sodium was a significant risk factor for hyponatremia during preparation for RAI therapy.Preparation for RAI therapy by THW or LID is not a risk factor for the development of hyponatremia in patients with thyroid cancer. The development of hyponatremia was neither frequent nor severe during preparation for RAI therapy. Physicians should not be greatly concerned about rare life-threatening hyponatremia during preparation for RAI therapy.

Hypothyroidism and hyponatremia: data from a series of patients with iatrogenic acute hypothyroidism undergoing radioactive iodine therapy after total thyroidectomy for thyroid cancer

PURPOSE

The aim of the present study was to evaluate the role of hypothyroidism as a cause of hyponatremia in a clinical model of iatrogenic acute hypothyroidism due to thyroid hormone withdrawal prior to ablative radioactive iodine (RAI) therapy after total thyroidectomy.

METHODS

The study group consisted of 101 differentiated thyroid cancer (DTC) patients (77 women and 24 men). Plasma concentration of thyroid-stimulating hormone ([TSH]) and sodium ([Na⁺]) was evaluated before total thyroidectomy (pre[TSH] and pre[Na⁺]) and on the day of RAI therapy (post[TSH] and post[Na⁺]).

RESULTS

The frequency of hypothyroidism-associated hyponatremia was 4 % (4/101). Pre[Na⁺] was significantly higher than post[Na⁺] (140.7 ± 1.6 vs 138.7 ± 2.3 mEq/L, p = 0.012). Moreover, a linear correlation was identified between pre[Na⁺] and post[Na⁺].

CONCLUSIONS

Iatrogenic acute hypothyroidism-related hyponatremia is uncommon. However, because of the significant reduction of [Na⁺] in the transition from euthyroidism to iatrogenic hypothyroidism, the value of pre[Na⁺] should be viewed as a parameter to be considered. Since it acts as an independent risk factor for the development of hyponatremia, patients with a pre[Na⁺] close to the lower limit of normal range may deserve a closer monitoring of [Na⁺].

Prevalence of Hyponatremia in Hypothyroid Patients during Radioactive ¹³¹I Ablation for Differentiated Thyroid Cancer: Single Institution Experience

BACKGROUND

Hyponatremia developing in hypothyroid patients has been encountered in clinical practice; however, its prevalence has not been well established.

METHODS

Thirty patients diagnosed with differentiated thyroid cancer, rendered hypothyroid after surgery and levothyroxine withdrawal, and who are for radioactive iodine (RAI) ablation were included. Serum sodium concentrations were measured twice, at the time of admission for RAI ablation, and before discharge after increased oral fluid intake. The outcome measures were to determine the prevalence of hyponatremia among hypothyroid patients prior to RAI ablation and after oral hydration post-RAI, and to correlate the serum sodium levels pre-RAI and post-RAI with thyroid-stimulating hormone (TSH) concentration and age.

RESULTS

Thirty patients were included, with ages from 23 to 65 years old (median, 40). Two patients (6.7%) were hyponatremic prior to RAI ablation, and eight patients (26.7%) had mild hyponatremia (130 to 134 mEq/L) after RAI and hydration. There was no significant correlation between TSH levels and serum sodium levels prior to or after RAI. There was also no significant correlation between pre- and post-RAI sodium concentration and age.

CONCLUSIONS

The prevalence of hyponatremia pre-RAI was 6.7%, and 26.7% post-RAI. No significant correlation was noted between TSH concentration and age on pre- or post-RAI sodium concentrations. Routine measurement of serum sodium post-RAI/isolation is still not advised. Measurement of sodium post-RAI may be considered in patients who are elderly, with comorbid conditions or on medications.

Low iodine diet in differentiated thyroid cancer: a review

Radioactive iodine (RAI) ablation is a beneficial, adjuvant therapy for the management of differentiated thyroid cancer (DTC) after thyroidectomy. The goal of RAI is to destroy remnant thyroid and microscopic cancerous tissue. Radioactive iodine uptake is enhanced by elevating TSH levels and initiating a low iodine diet (LID) prior to ablation. An ideal LID should preferably not exceed 50 mcg/day of dietary iodine for 1-2 weeks, although the duration may be shortened to a week with a structured patient education programme. A pre-ablation spot urinary iodine concentration (UIC) of <100 mcg/l and/or a urinary iodine to creatinine ratio (UICR) of <100 mcg/gCr would support an adequate LID preparation. Hyponatraemia, most likely due to iatrogenic hypothyroidism, is a potential side effect associated with LID and occurs during and a few days after the LID. Although the overall incidence of hyponatraemia is low, patients at high risk (older age, female sex, use of thiazide diuretics) may benefit from serum sodium monitoring. The existing evidence on the impact of LID on RAI ablation has been largely inconsistent due to retrospective study designs and the lack of an objective measurement of urinary iodine levels. Future large prospective randomized control trials are needed to elucidate and confirm the crucial role of LID in achieving successful RAI ablation and greater disease-free survival in DTC.