Ultrasound-guided microwave ablation for tertiary hyperparathyroidism in patients with renal transplantation

Abstract Objective To explore the safety and efficacy of ultrasound-guided microwave ablation (MWA) for tertiary hyperparathyroidism (THPT) in patients with renal transplantation (RT). Methods In total, fifteen patients with THPT after renal transplantation who underwent MWA were enrolled in the study. The pre- and post-MWA intact parathyroid hormone (iPTH), serum calcium, phosphorus, creatinine, urea nitrogen and estimated glomerular filtration rate (eGFR) values were compared. Results A total of 38 parathyroid hyperplastic nodules in 15 RT patients were treated with ultrasound-guided MWA. The mean (median, range) size of the hyperplastic parathyroid nodules was 11.5 mm (11 mm, 5–25 mm), and the average (median, range) ablation time was 163.5s (121 s, 44–406 s). The average levels of serum iPTH and calcium at 1 d, 7 d, 1 month, 3 months, 6 months, 1 year post-MWA and at the end of follow-up were significantly lower than those pre-MWA (all p < 0.05). Compared with the pre-MWA value (0.76 mmol/L), the serum phosphorus levels at 1 d post-MWA (0.63 mmol/L) were significantly decreased, and those at 7 d, 1 month, 3 months, 6 months, 1 year post-MWA and at the end of follow-up were significantly increased, but all were within the normal range. There was no significant difference in serum creatinine and eGFR pre-MWA and post-MWA. No major MWA-related complications occurred. Conclusion Ultrasound-guided MWA shows potential as a viable treatment for THPT in RT patients. However, further studies are required to confirm its safety and effectiveness in larger cohorts of longer duration.


Introduction
Tertiary hyperparathyroidism (THPT) is a serious complication of long-term secondary hyperparathyroidism, in which the parathyroid cells are persistently and strongly stimulated, causing partial hyperplastic tissue to transform from polyclonal to monoclonal proliferation or adenoma with functional hyperactivity.It is not inhibited by feedback such as high calcium, and spontaneously secretes excessive PTH, leading to a series of clinical symptoms such as bone pain and skin itching [1][2][3].THPT mainly occurs in patients with chronic renal failure complicated with renal osteodystrophy.Some patients have persistently high levels of parathyroid hormone (PTH) alongside hypercalcemia, even after renal transplantation.In severe cases, THPT can lead to renal graft dysfunction and loss and affect the prognosis of such patients [4,5].
THPT has been reported to occur in 17%-50% of renal transplant patients, and timely treatment is essential for the maintenance of graft function [2,6].At present, the main treatments for THPT include medical therapy and parathyroidectomy.Studies have shown that the use of the calciumlike agent cinacalcet has certain efficacy in the treatment of THPT after renal transplantation [2,7].The study from Dulfer et al. [8] showed that cinacalcet could significantly reduce the level of serum calcium.The study of Greeviroj et al. also showed that cinacalcet could simultaneously reduce the levels of serum iPTH, blood calcium, and phosphorus [9].However, some patients may stop cinacalcet due to side effects such as vomiting, diarrhea, and even hypocalcemia [10].Moreover, medical therapy only temporarily relieves these symptoms and is not a cure for the cause of the symptoms.
Currently, surgical resection is the only method that can cure THPT and includes subtotal parathyroidectomy and total parathyroidectomy with or without autotransplantation.An RCT conducted by Cruzado et al. [11] showed that all 15 renal transplantation patients with THPT who underwent parathyroidectomy achieved normocalcemia.Other studies [12,13] have also demonstrated the efficacy of surgical parathyroidectomy in renal transplantation patients.However, some studies [14,15] have shown that patients with parathyroidectomy have a permanent decline in renal function, although graft survival was not affected.Landa et al. [16] found that this may be related to the vasodilatory effect of PTH in improving the intrarenal microenvironment.
Ultrasound-guided percutaneous ablation is an emerging minimally invasive technique that has the advantages of reduced trauma, cost-effective treatment, and reliable efficacy, making it increasingly used in clinical practice.Among various percutaneous ablation methods, microwave ablation (MWA) stands out due to its superior thermal efficiency [17].However, to the best of our knowledge, there have been no studies on MWA for the treatment of THPT after renal transplantation.Therefore, this study aims to evaluate the safety and effectiveness of ultrasound-guided MWA in patients with THPT after renal transplantation and to investigate any potential adverse effects associated with MWA and its impact on the overall function of renal transplantation.

Patient population
All imaging examinations and microwave ablation procedures were carried out with the patient's informed consent.This retrospective study received approval from the institutional ethics committee (No. 2019 (330)), and the requirement for informed consent was waived.In total, fifteen patients who developed THPT after renal transplantation and underwent ultrasound-guided microwave ablation at our hospital between February 2020 and March 2023 were included in the study.The inclusion criteria were as follows: (1) successful kidney transplantation; (2) the serum iPTH � 300 pg/mL, or iPTH < 300 pg/mL combined with serum calcium > 2.5 mmol/L; (3) resistance to medical therapy; (4) inability or unwillingness to undergo open surgery; and (5) hyperplastic nodules of the parathyroid glands located by ultrasound with a safe puncture path.The exclusion criteria were patients with severe coagulation disorders, hyperplastic lesions with a risk of malignancy, and 99m Tc-MIBI scans showing ectopic hyperplastic nodules of the parathyroid glands outside the neck.

Ultrasound-guided percutaneous microwave ablation procedure
An EPIQ7 ultrasound system (Royal Philips, the Netherlands) equipped with an L12-5 (5-12 MHz) transducer was used to guide microwave ablation.Contrast-enhanced ultrasound (CEUS) was performed with the same equipment using a real-time, low-mechanical index (MI: 0.05-0.08)and reverse pulse imaging technique.In total, 2.4 ml of the SonoVue ultrasound contrast agent (Bracco, Milan, Italy) was injected into the medial cubital vein and immediately flushed with 5 ml of 0.9% sodium chloride solution.Microwave ablation was performed with a microwave generator (Microwave Tumor Ablation System, Nanjing GreatWall Medical Equipment Co., Nanjing, China) and a special 17-gauge needle for thyroid ablation (XR-A1610W, Nanjing GreatWall Medical Equipment Co., Nanjing, China).
Before performing MWA, ultrasonography, and 99mTc-MIBI examinations were conducted to determine the location and number of hyperplastic parathyroid nodules and to evaluate the ultrasound-guided percutaneous puncture path (Figure 1).In the preparation process of MWA, there were certain small nodules of parathyroid hyperplasia that could not be detected by MIBI due to its low resolution.Meanwhile, parathyroid fine needle aspiration biopsy (FNAB) is not recommended due to its ineffectiveness in differentiating parathyroid hyperplasia, adenoma, and adenocarcinoma.Additionally, there are risks of bleeding and implantation after the procedure [18].Therefore, our ablation strategy encompassed performing MWA for all hyperplastic parathyroid nodules visible on MIBI.Moreover, MWA was also carried out for nodules that weren't detectable on MIBI but were discernible through ultrasound imaging.The entire MWA process was conducted under real-time ultrasound monitoring.The ablation procedure was performed as follows: The patient was in a supine position with the head tilted back to fully extend the neck and expose the anterior neck area.The anterior neck area underwent sterilization, followed by the placement of a surgical drape.To maintain sterility, the ultrasound probe was shielded with a sterile protective sleeve.Local anesthesia was administered using a 2% lidocaine solution.Subsequently, hydro dissectionhydro dissection with a thickness of at least 5 mm was established around the hyperplastic parathyroid nodule using a dilution of 2% lidocaine and saline (lidocaine: saline ¼ 1:3-1:4), and an indwelling tube was placed to allow for replenishment of the isolation fluid as needed.Initially, hydrodissection was established on the tracheal side of the nodule, followed by the lateral side.Ultrasound-guided MWA of the hyperplastic parathyroid nodules was performed by an experienced interventional ultrasound physician.The ablation power used was 30 W, and site-directed ablation was performed in cycles of 30 s, with 2-3 cycles for each site until a strong echoic bubble covered the entire parathyroid nodule, including a portion of the normal parathyroid tissue.The ablation range is at least 12.3 mm (length) x 6.7 mm (width) when the ablation time exceeds 20 s with a power of 30 W. In cases where hyperplastic nodules were found in both parathyroid glands, the side with more and larger hyperplastic nodules was ablated first.Following the ablation procedure on one side, the patient was observed for thirty minutes before proceeding with the ablation on the other side.Alternatively, ablation on the second side could be performed on a separate day, but this would result in additional costs for the patient.For hyperplastic parathyroid nodules on the same side, the nodules in the inferior parathyroid were usually ablated first, followed by those in the superior parathyroid.Throughout the ablation procedure, the patient's voice was closely monitored for any changes, and if hoarseness occurred, the ablation was immediately halted.Contrast-enhanced ultrasound was performed immediately after ablation to determine if necrosis had occurred within the nodules.Any areas showing residual enhancement were subjected to additional rounds of ablation.Local pressure was applied for 30 min after the operation using an ice pack, and the patient was closely observed.

Data collection and follow-up
The levels of serum iPTH (measured by chemiluminescence immunofluorescence methods), serum calcium, phosphorus, creatinine, urea nitrogen, and eGFR were collected before MWA and at 1 d, 7 d, 1 month, 3 months, 6 months, 1, 2 and 3 years post-MWA.All laboratory indicators were obtained in our hospital.The location, number, size, and sonographic features of the hyperplastic parathyroid nodules before ablation, ablation power, ablation time, and number of ablated nodules during the operation, and postoperative complications were recorded.Neck ultrasound was performed 24 hours after ablation to exclude severe complications such as neck hematoma.SPSS 22.0 statistical software (IBM, NY, USA) was used to perform data analysis.Continuous data are expressed as the mean ± SD.The Mann-Whitney tests were used to compare the pre-MWA serum iPTH, serum calcium, phosphorus, creatinine, urea nitrogen and eGFR values with those obtained 1 d, 7 d, 1 month, 3 months, 6 months, 1 year post-MWA treatment and the end of follow-up.Differences were considered significant at p < 0.05.

Patient and clinical characteristics
The characteristics of the included patients are shown in Table 1.A total of 15 renal transplantation patients with THPT were enrolled in the study, including 3 females and 12 males.The age ranged from 28 to 51 years, with an average age (median) of 38.7 (37) years.The interval between kidney transplantation and microwave ablation ranged from The arrows on the left side of figures G and H indicated the inferior aspect of thyroid gland that has been damaged by MWA, and the arrows on the right side showed the alterations observed after the MWA of hyperplastic nodule in the parathyroid gland, which were both presented as hypoechoic on two-dimensional ultrasound, and no enhancement on CEUS one month later.(I) One year later, MIBI showed that the radiation distribution was uniform in the thyroid region, and there was no localized increase in 99mTc uptake around the thyroid gland or in the upper mediastinal region.
6 months to 72 months (median, 8 months).A total of 38 hyperplastic nodules of the parathyroid glands were treated with ultrasound-guided microwave ablation.The average nodule diameter (median) was 11.5 (11) mm, ranging from 5 to 25 mm.In total, three patients had single nodules, 3 patients had 2 nodules, 7 patients had 3 nodules, and 2 patients had 4 nodules.Of these nodules, four were located posterior to the upper part of the right lobe of the thyroid, 19 were located posterior to the lower part of the right lobe of the thyroid, 3 were located posterior to the upper part of the left lobe of the thyroid, and 12 were located posterior to the lower part of the left lobe of the thyroid.
Prior to the ablation procedure, all hyperplastic nodules exhibited hypoechoic characteristics with well-defined shapes and boundaries.Moreover, CEUS showed hyperenhancement in 7 nodules, isoenhancement in 13 nodules, and mild hypoenhancement in 18 nodules.All 38 nodules were completely ablated in one session, and the average ablation time (median) for each nodule was 163.5 (121) s, ranging from 44 to 406 s.CEUS showed no enhancement of the nodules after ablation.To date, no patients have been found to develop recurrent hyperplastic parathyroid nodules according to postoperative ultrasound and MIBI follow-up.
Before MWA, five patients received 75 mg cinacalcet once a day, 3 patients received 50 mg cinacalcet once a day, and 3 patients received 25 mg cinacalcet once a day before MWA.After MWA, one patient received 50 mg of cinacalcet once a day, 5 patients received 25 mg of cinacalcet once a day, 4 patients received 25 mg of cinacalcet every other day, and one patient stopped taking cinacalcet.The remaining 4 patients did not take cinacalcet before MWA or after MWA.The average daily dose of cinacalcet post-MWA (27 mg) was significantly reduced compared with that of pre-MWA (65 mg) (p ¼ 0.003).

Discussion
Tertiary hyperparathyroidism (THPT) is a common complication after renal transplantation (RT) and can even result in allograft loss.However, there are no guidelines for the standard treatment of THPT, especially for patients with RT.To our knowledge, this is the first study on ultrasound-guided microwave ablation for the treatment of THPT in RT patients.The results showed that MWA was effective in the treatment of THPT and had no significant effect on allograft function.
THPT is typically characterized by hypercalcemia and hypophosphatemia, which can increase the all-cause mortality of RT patients [4].Thus, the primary objective of THPT treatment is to normalize blood calcium levels.The preferred agent for medical therapy is cinacalcet, which is a calcimimetic agent that enhances the sensitivity of calcium-sensing receptors in the parathyroid gland and then inhibits the secretion of parathyroid hormone.A systematic review conducted by Dulfer et al. assessed the efficacy of cinacalcet in treating THPT after renal transplantation [2].The study revealed that cinacalcet could normalize the serum calcium level in 80.8% (240/297) of patients.However, 6.4% of patients terminated medical treatment due to side effects.Nevertheless, the effect of cinacalcet on renal allograft function and patient survival needs to be further studied.
Parathyroidectomy is a radical cure for the majority of patients with THPT [19,20].However, this procedure has a high degree of surgical trauma and can easily result in residual nodules in patients with small and multiple lesions [17,21].Additionally, total parathyroidectomy may have some complications, which could result in lifelong replacement therapy.Therefore, it is worthwhile to explore whether MWA can help address some of the issues faced by renal transplant patients who cannot tolerate or are unwilling to undergo surgery again.In this study, the levels of serum iPTH and calcium at 1 d, 7 d, 1 month, 3 months, 6 months, and 1 year after MWA and at the end of follow-up were significantly lower than those before MWA.It is worth mentioning that blood calcium levels after MWA remained within the normal range, and the maximum follow-up time was 41 months, which is consistent with previous studies on ultrasound-guided percutaneous MWA for secondary and tertiary hyperparathyroidism [17,22,23].In addition, the serum phosphorus levels were significantly decreased at 1 d after MWA, while the serum phosphorus levels increased significantly from 7 d after MWA until the end of the follow-up period but remained within the normal range, which may be related to the evident decrease in iPTH levels following MWA.However, the study from Hu et al. showed that the blood phosphorus levels decreased gradually after MWA and reached stable levels after 6 months [23].The study from Li et al. showed that the blood phosphorus levels were significantly increased at 1 month after MWA compared with those before MWA, but were significantly decreased at the end of follow-up [22].Although the changes in serum phosphorus levels in these studies differed, the blood phosphorus concentration in these studies remained within the normal range.
Several studies have shown that parathyroidectomy decreases renal allograft function, which is sometimes a permanent reduction [24][25][26].Therefore, we further investigated the effect of MWA on renal function in renal transplant patients.The results of this study revealed slight increases in urea nitrogen levels on the first postoperative day, which subsequently returned to preoperative levels.However, However, there were no significant increases observed in serum creatinine and eGFR.These results suggest that MWA is not obviously harmful to renal function in the treatment of THPT in RT patients and that this transient increase in urea nitrogen on the first postoperative day may be caused by the stress response to MWA.Moreover, the study from Li et al. indicated that blood creatinine and urea nitrogen were not significantly different pre-MWA and post-MWA, while the data they presented showed a slight increase in serum creatinine on the first day post-MWA compared to that pre-MWA [22].However, the number of patients included in these studies was relatively small, and the duration of followup was limited.Therefore, studies with larger sample sizes and longer follow-up periods are needed to further determine the effect of MWA on renal allograft function.
It is worth mentioning that in our clinical practice, a certain dose of cinacalcet was indeed given to the patient according to the individual actual condition after MWA of parathyroid hyperplasia nodule.However, most patients needed to take a large amount of cinacalcet every day before MWA in the study, while their clinical symptoms have not been significantly improved.Nevertheless, MWA of parathyroid hyperplasia nodule can not only significantly improve the clinical symptoms of the patients, but also significantly reduce the dose of cinacalcet, or even stop taking it.However, more evidence is needed to confirm the effect of MWA alone for the treatment of THPT in RT patients.In addition, there were no major MWA-related complications in this study, and the only three patients who developed complications, such as hoarseness and pharyngalgia, recovered spontaneously without medical intervention.Nonetheless, there were several limitations in our study.First, this was a single-center and retrospective study, and a prospective study is needed to verify the results.Second, since only patients with THPT after renal transplantation were included, the number of patients was relatively small, and validation with large cohorts is needed.Third, the follow-up time in this study was relatively short, with a mean follow-up time of 30.1 months.To better determine the efficacy of MWA in the treatment of THPT in RT patients, a longer follow-up time is needed.
In conclusion, based on our study findings, it appears that ultrasound-guided MWA holds promise as a treatment option for tertiary hyperparathyroidism in renal transplant patients without causing substantial harm to renal allograft function.Nevertheless, further investigation is required to confirm its safety and effectiveness in larger cohorts of longer duration.

Disclosure statement
No potential conflict of interest was reported by the author(s).

Figure 1 .
Figure 1.Ultrasound-guided microwave ablation of tertiary hyperparathyroidism in a 48-year-old male patients with successfully renal transplantation.(A) Twodimensional ultrasonography revealed a hypoechoic nodule with a diameter of 14 mm was located posterior to the lower part of right lobe of thyroid before microwave ablation (MWA).(B) Contrast-enhanced ultrasound showed the nodule with heterogeneous iso-enhancement.(C) MIBI scan showed the nodule with increased radioactivity concentration in the late phase.(D) SPECT/CT fusion imaging revealed a low-density nodule posterior to the inferior pole of right lobe of the thyroid, which showed a localized increase in 99mTc-MIBI uptake at 1 h after 99mTc-MIBI injection.(E) The nodules were filled with gas-like hyperechoic during MWA.(F) Contrast-enhanced ultrasound (CEUS) preformed immediately after MWA showed a non-enhancement area complete covered the nodule.(G)The arrows on the left side of figures G and H indicated the inferior aspect of thyroid gland that has been damaged by MWA, and the arrows on the right side showed the alterations observed after the MWA of hyperplastic nodule in the parathyroid gland, which were both presented as hypoechoic on two-dimensional ultrasound, and no enhancement on CEUS one month later.(I) One year later, MIBI showed that the radiation distribution was uniform in the thyroid region, and there was no localized increase in 99mTc uptake around the thyroid gland or in the upper mediastinal region.