ESPE Abstracts

Case presentation: We recently started a 9-year-old girl with hypoparathyroidism due to a mutation in the PTH gene on a pump therapy with 1–34 rhPTH. She has received calcitriol and calcium since the age of 4 months. Bilateral nephrocalcinosis stage II/III was diagnosed at a young age. So far, her renal function remains normal. During the last 18 months symptomatic hypocalcemic episodes have become more frequent despite increased calcium and calcitriol doses. Continuous rhPTH therapy was considered, encouraged by positive reports in the literature. 4 weeks before rhPTH therapy started, we gave her an i.m. depot with 100.000IU of 25-OH-D and stopped calcitriol therapy. The initial rhPTH dose was 0.5 μg/kg per day. Serum calcium, phosphate, crosslaps (CTX), osteocalcin and 1–34 PTH were measured every 2 h during the first 48 h of therapy. We observed mild nausea at the beginning of the therapy, when the calcium levels increased. The calcium: creatinine ratio in urine normalized during the first 24 h and gradually increased over the next 48 h, which together with serum calcium levels in the upper normal range made a decrease in dose necessary. After 2 weeks, serum calcium levels of around 2.5 mmol/l have been established without additional oral calcium supplementation. However, urinary calcium excretion is still high. We documented interesting courses of endogenous calcium regulation in this human model of genetic PTH deficiency during the first days of exposure to rhPTH therapy. Both P1NP and osteocalcin levels increased by approx. 20% in the first 12 h of therapy in parallel with an initial increase in serum calcium. Levels then dropped to sub-baseline after 24 h. Regarding bone resorbtion, there was a biphasic elevation of CTX during continuous rhPTH application: CTX levels dropped after an initial peak in the first 24 hours but increased again after approx. 4 days. We speculate that after an initial effect on bone resorbtion, PTH-induced maturation of osteoclast precursors led to the delayed effects observed after 96 h. We hypothesize that activation of bone resorbtion rather than increased calcium uptake accounts for most of the initial increase in serum calcium during rhPTH treatment.