SAT-391 Safety and Efficacy of Conventional Therapy with Calcium and Activated Vitamin D in Patients with Chronic Post-Operative Hypoparathyroidism: Results of a Cross-Sectional Case-Control Study

Introduction: Conventional therapy of chronic post-operative hypoparathyroidism (PO-HypoPT) with calcium and activated vitamin D is suboptimal and associated with several complications, including impairment of the quality of life. Aim of this study was to compare clinical, biochemical and instrumental parameters in 120 patients who underwent total thyroidectomy for differentiated thyroid cancer, 60 with PO-HypoPT (Group A) treated with conventional therapy and 60 without (Group B), matched for age and sex, followed a tertiary referral center. Matherials and methods: An “ad hoc” CRF was used to collect epidemiological, clinical (symptoms, treatment) and biochemical data (total and ionized calcium, albumin, phosphate, magnesium, calcium/phosphate product, creatinine, 25-OH vitamin D, PTH, TSH, eGFR, 24-h urinary calcium and creatinine), and renal ultrasound. Results: The median duration of PO-HypoPT was 7 years (IQR 4-13). All patients of group A were treated with calcitriol (median 0.5 μg/daily; IQR 0.5-1.0), and 33/60 (55%) were also given calcium carbonate supplementation (median 1000 mg/daily; IQR 500-1000). Hypocalcemia related symptoms were more frequent in group A (27/60 - 45%) than in group B (1/60 - 1.7%) (p<0.01). Total and ionized serum calcium [median 8.9 (IQR 8.5-9.1) vs 9.3 (IQR 9.0-9.5) mg/dl; median 1.16 (IQR 1.1-1.2) vs 1.23 (IQR 1.21-1.27) mmol/L] (p<0.01), magnesium [median 1.9 (IQR 1.8-2.0) vs 2 (IQR 1.9-2.1) mg/dl - p<0.01] and PTH [median 10 (IQR 8-13) vs 29 (IQR 22-35) pg/ml - p<0.01] were significantly lower in Group A vs Group B. Conversely, serum phosphate [median 3.7 (IQR 3.4-4.1) vs 3.3 (IQR 3.0-3.6) mg/dl - p<0.01], calcium-phosphate product [median 33 (IQR 30-36) vs 30 (IQR 27-34) - p=0.012] and 25-OH vitamin D [median 34.1 (IQR 29.2-41.3) vs 26.7 (IQR 18.1-33.4) - p<0.01) were significantly higher in Group A vs Group B. Twenty-four hour urinary calcium was higher in group A [median 248 mg (IQR 166-363)] than in group B [median 165 mg (IQR 94-229)] (p<0.01). The rate of nephrolithiasis was significantly higher in group A (21/60 pts - 35%) than in group B (7/60 pts - 11.7%) (p<0.01). Moreover, there was a significant correlation of neprholithiasis with 24h urinary calcium but not with total and ionized serum calcium. Conclusions: This cross-sectional case-control study confirms that treatment of chronic PO-HypoPT with conventional therapy is suboptimal, even in a tertiary referral center, and associated with an increased risk of nephrolithiasis. Following the recent publication of treatment guidelines, the question of whether a better quality of care, including the use of rhPTH, will improve the biochemical control and decrease the rate of hypercalciuria and the risk of nephrolithiasis remains to be established.