Supplementary Material for: Calcium-Alkali Syndrome Associated with Hypoparathyroidism Following Total Thyroidectomy

Background: Patients with permanent postsurgical hypoparathyroidism, a complication of total thyroidectomy, often require high calcium supplementation with vitamin D to maintain serum calcium levels. The epidemiology of calcium-alkali syndrome (CAS) in patients with hypoparathyroidism after total thyroidectomy remains unclear. This study aimed to investigate the incidence of hypercalcemia, renal impairment, metabolic alkalosis, and CAS in patients treated for presumed hypoparathyroidism after total thyroidectomy. Methods: Twenty-seven patients with neck cancers who underwent total thyroidectomy without parathyroid autotransplantation between January 2010 and October 2013 at our hospital were consecutively included. All patients received calcium lactate and alfacalcidol for postsurgical hypocalcemia. We defined hypercalcemia as a corrected serum calcium level (cCa) ≥10.5 mg/dL, metabolic alkalosis as a difference in serum sodium and serum chloride ([sNa-sCl]) ≥39 mEq/L, and renal impairment as a ≥50% increase in serum creatine and/or ≥35% decrease in estimated glomerular filtration rate (eGFR) compared to baseline. Results: cCa peaked (11.1 ± 1.5 mg/dL) at a median of 326 days (interquartile range 78–869) after surgery. At peak cCa, [sNa-sCl] was significantly higher (p < 0.01), and eGFR was significantly lower (p < 0.01) than that at baseline. Fifteen patients (55.6%) had hypercalcemia, 19 (70.3%) had alkalosis, 12 (44.4%) had renal impairment, and 9 (33.3%) had CAS. Patients with CAS (mean age 67.1 ± 10.8 years) were older than those without CAS (56.7 ± 13.6 years, p = 0.06). The mean dose of alfacalcidol in the CAS group (3.1 ± 1.2 μg/day) was significantly larger than that in the non-CAS group (2.1 ± 1.0 μg/day, p = 0.03). Conclusions: This retrospective study reveals the high incidence of CAS in patients with hypoparathyroidism after total thyroidectomy. Furthermore, these findings suggest that the serum calcium level, acid-base balance, and renal function should be closely monitored in patients with postsurgical hypoparathyroidism who receive large doses of active vitamin D.