2. Materials and Methods

2.1. Ethics statement

This study was approved by University of Health Sciences Antalya Training and Research Hospital Ethics Committee and written informed consent was obtained all patients before procedure

2.2. Study design and the patients

Thirty-two patients with PHPT from February 2017 to August 2020 who are eligible to study protocol were included. The adenoma of all patients enrolled in the study were thought to be benign. In case of malignancy findings, surgical resection was recommended instead of fine needle aspiration biopsy 16. The inclusion criteria, based on the guidelines 4 were as follows: patients with symptomatic PHPT; patients with asymptomatic PHPT, whose serum Ca concentration is at least 0.25 mmol/L higher than the upper limit of normal range; who have skeletal involvement as a decrease in bone mineral density patients with renal involvement as creatinine clearance less than 60 ml/min, nephrolithiasis or nephrocalcinosis, patients who have hypercalciuria (>10 mmol per day) or patients younger than 50 years old. Preablation data of the study group was summarized in Table 1.
For the prediction assay, age, gender, parathyroid adenoma volume, microwave ablation time (sec) and power (Watt), baseline level of Ca, phosphorous (P), alkane phosphate (ALP) and PTH, vitamin D level, location of parathyroid adenoma were recorded. Afterwards, depending on the treatment efficacy, which has the criteria of treatment success if the six-month follow-up of PTH has lesser than 88.0 ng/L and Ca is at the normal range, patients divided into response and no response groups. Then, the predictive abilities of the potential factors were investigated by logistic regression to evaluate its role in the MWA efficacy.

2.3. Laboratory assessment

Ca, P, ALP, PTH, and Vitamin D levels were measured before the MWA procedure and 1 day, 1 month, and 6 months after MWA therapy. Ca, P and ALP were measured using AU5800 Series Chemistry Analyzers (Beckman Coulter Inc., Brea, CA, USA). PTH and vitamin D levels were measured with Dx1 800 DxI 800 Access Immunoassay System (Beckman Coulter Inc., Brea, CA, USA). The normal ranges were as follows: Ca, 2.2-2.65 mmol/L; P, 0.81-1.45 mmol/L, PTH, 12-88 ng/L; ALP, 30-120 u/L and vitamin D, 74.8-249.6 nmol/L. The volume and the location of parathyroid adenomas were localized by ultrasound and 99mTc sestamibi (MIBI). Parathyroid wash out was only performed when the lesion could not be clearly localized with these imaging methods.

2.4. Microwave ablation procedure

Three orthogonal diameters of the parathyroid adenoma were measured before ablation and follow-up with a real-time ultrasound system with a 5-14 MHz linear probe. The volume of the nodule was calculated automatically through the software program of the Aplio 500, Toshiba Medical Systems, Tokyo, Japan. Microwave ablation system (ECO-100AI3), consisting of a microwave generator producing 30-40 W of power at 2450 MHz either continuously or in a pulse; a flexible cable, and internally-cooled 16-gauge thyroid antenna with 10 cm shaft length with a 3 mm active tip was used. Parathyroid adenoma ablation was performed on an outpatient basis under local anesthesia without sedation. The patient was placed in a supine position with the neck mildly hyperextended. After determining the appropriate puncture side, a mixture of 30/70% lidocaine (Osel Pharmaceuticals, Istanbul, Turkey) and saline was applied along the puncture path from the skin to the thyroid capsule after then infused into the surrounding thyroid capsule to protect vital recurrent laryngeal nerves, esophagus and trachea adjacent to the parathyroid adenoma. Internally cooled thyroid microwave ablation antenna was positioned under ultrasound guidance via trans-isthmic approach or lateral cervical approach. A moving shot technique was used to ablate the parathyroid adenoma throughout the procedure. Therapy was completed when the entire nodule was covered with hyperechoic microbubbles, which is used indicative of ablation. Heart rate and oxygen saturation were continuously monitored during the procedure. After the procedure, all patients were followed by cold compression to prevent neck hematoma. The patients who were informed about the symptoms of hypocalcemia were discharged after 4 hours of follow-up.

2.5. Statistical analysis

The analysis of data was conducted by SPSS® 20.0 (Statistical Packages for Social Sciences; SPSS Inc, Chicago, Illinois, USA). The normality of the data was assessed with Shapiro-Wilk test of normality (P >0.05). All the normally distributed continues variables were presented as mean ± standard deviations whereas the rest and the categorical variables were reports as median (interquartile ranges) and percentages. Due to the non-normal distribution in Ca, P, ALP and PTH values, Friedman and Wilcoxon’ signed rank tests was used in their comparison with time difference. Mann-Whitney U test was used for the comparison of the values in two non-normal distributed groups. Fischer exact test was also used to compare categorical variables between response and no response groups. The significance level was based on a P value of less than 0.05.
Age, gender, Parathyroid adenoma volume, baseline levels of Ca, P, ALP, vitamin D, location of parathyroid adenoma, microwave ablation time and power were compared and identified as possible predictive factors between response and no response group. The no response group was considered as the control group. The differences between the control group and the response group were evaluated by using Mann-Whitney U and χ2 test. The detailed further investigations of the possible factors were explored by using logistic regression.