Study on the Effects of Hypoparathyroidism on Post-thyroidectomy Health-related Quality of Life (QoL-hPTP)

Patients submitted to total thyroidectomy according to clinical practice will be invited to participate in this study. If they accept, they will have to complete three questionaries to evaluate their HRQoL: SF-36, Hospital Anxiety and Depression Scale (HADS) and a specifically designed Likert-type questionary about the intensity of hypoparathyroidism symptoms; the day before the surgery and one week and one month after it. In those cases that develop permanent hypoparathyroidism, an additional evaluation will be done 3, 6, 9 and 12 months after surgery.

Variables:

• Demographic variables: sex, age, BMI, personal background, previous treatment.
• Diagnosis variables: diagnosis, cytology (Bethesda System), preoperative laboratory values serum (albumin, glomerular filtrate rate, total and ionic calcium, phosphate, magnesium, parathormone (PTH), 25-hydroxide (OH) vitamin D, thyroid-stimulating hormone (TSH), T4, thyroid antibodies).
• Procedure variables: central compartment dissection, accidental parathyroidectomy, parathyroid autotransplant, surgery length, intraoperative complications.
• Post-operative variables:
• Laboratory test 24h after surgery: albumin, glomerular filtrate rate, total and ionic calcium, phosphate, magnesium, PTH, 25-OH vitamin D.
• Symptoms of Hypocalcemia: presence of spontaneous symptoms of hypocalcemia, such as paresthesias, and time from the surgery (measured in hours).
• Postoperative hypocalcemia: defined by a serum albumin-corrected calcium level below 8 mg/dL or by the presence of hypocalcemic symptoms that require calcium or vitamin D supplementation.
• Follow-up variables: all the patients will be evaluated one week and one month after surgery. When they develop a hypocalcemia, laboratory test will be repeated according to clinical practice. In all cases, this test will be repeated one month after surgery, together with thyroid function test. The need for oral supplementation of calcium and/or vitamin D analogs or even magnesium will be collected (doses and time needed). The definitive histological diagnosis and the number of additional parathyroid glands identified in the surgical specimen will be also collected. In cases that developed postoperative hypocalcemia, the investigators will record the time to resolution, defined as the absence of calcium or vitamin D supplementation and a PTH level above 13 pg/mL.

Statistical Analysis:

The patients will be divided into two group depending on the development of post-thyroidectomy hypoparathyroidism. The results of their HRQoL questionaries will be compared within both groups. The investigators will evaluate the influence of clinical variables on these results.

The quantitative variables that follow a normal distribution will be described by the mean and the standard deviation; and those who do not follow the normal distribution will be described by median and interquartile range. The qualitative variables will be defined by the number of events and the percentage. To know if the variable follow or not the normality the investigators will use de Kolmogorov-Smirnov test.

The quantitative variables with a normal distribution will be compared with Student t-test (if there are two means) or with ANOVA (for more than two means). To compare quantitative variables with a different distribution, the Mann-Whitney U test (2 means) or Kruskal-Wallis test (more than 2) will be use.

The association between quantitative variable with a normal distribution will be stablished by the Pearson correlation ratio; and for those who do not follow the normal distribution, with Spearman test.

χ2 test will be used to compare qualitative variables. If an absolute frequency less or equal to 5 is found in any of the contingency table cells, the Fisher's exact test will be used.

Every test will be considered if there is a minimum signification level of p\<0,05.

Sample size calculation:

There is not enough published data in order to help us calculate a proper sample size. the investigators will conduce the first 40 patients as a pilot study, based on which it will estimate a definitive sample size. The investigators will take as reference the results of the SF-36 survey of the week after the surgery and a minimum difference to detect of the 10% of the punctuation.