Lenvatinib-induced hypocalcaemia due to transient primary hypoparathyroidism

Context: Radioiodine refractory differentiated thyroid cancer can be effectively treated with multi-tyrosine-kinase inhibitors (MKIs). Hypocalcaemia has been reported among the side effects of these drugs, but little is known about its pathophysiology and clinical relevance. Case report: We report the case of a 78-years-old woman with an aggressive papillary thyroid cancer infiltrating perithyroidal structures. The extent of surgery was limited to hemithyroidectomy, RAI treatment could not be performed, and she started lenvatinib treatment. After 4 months of therapy, the patient accessed the Emergency Department for a grade III hypocalcaemia (corrected serum calcium: 6.6 mg/dL, n.v. 8.1–10.4 mg/dL), due to primary hypoparathyroidism (serum PTH: 12.6 ng/L, n.v. 13–64 ng/L). The patient was treated with intravenous calcium infusions and vitamin D supplementation. After discharge, the oral dose of carbonate calcium (CaCO3) was of 6 g/day, and was titrated according to blood exams. Two weeks after discharge, while taking CaCO3 at the dose of 3 g/day, the patient experienced symptomatic grade II hypercalcemia (corrected serum calcium: 11.6 mg/dL), associated to the spontaneous reprise of PTH secretion, and leading to oral calcium withdrawal. During the subsequent follow-up, the patient remained eucalcemic without calcium supplementation. Conclusions: Though hypocalcaemia has been described as potential side effect of MKI treatment, this is the first report of a lenvatinib-induced primary hypoparathyroidism, in a patient with a documented normal parathyroid function after surgery. The periodical assessment of calcium-phosphorus metabolism is thus warranted to prevent this potentially lethal side effect, in both post-surgical hypoparathyroid and euparathyroid patients.