Remarkable improvement of bone mineral density concordant with calcium intake in hyperthyroidism patient with severe hypocalcemia following thyroidectomy – Case report

Background Hyperthyroidism is one of the causes of secondary osteoporosis, with increased bone turnover and decreased bone mineral density (BMD). Although antithyroid medication and surgical treatment can improve BMD, the association of calcium intake with an increase in postoperative BMD remains unclear. Case Presentation A 51-year-old postmenopausal woman after discontinuation of treatment for hyperthyroidism was diagnosed with thyrotoxicosis and osteoporosis with a high risk of fracture based on lumbar spine and femur BMD. She was prescribed antithyroid drug (methimazole 15mg/day) and alendronate (35mg/week). Following two months of administration, a thyroidectomy was performed, after which the patient noted numbness and cramps in the hands and feet, and was diagnosed with hypocalcemia (corrected serum calcium, 6.1mg/dL). Increasing the dosage up to the maximum of alfacalcidol (8µg/day) and calcium lactate (8000mg/day) resulted in improved symptoms and normalized serum calcium level. One year after surgery, the total amount of calcium supplement was 190g and estimated dietary calcium intake was 171g, for a total annual intake of 361g. On the other hand, the estimated total urinary calcium excretion amount for the year, calculated from urinary calcium and creatinine at each visit, was 82g. Concordantly, BMD in both lumbar spine and femur increased approximately 50%, presumably reflecting increases of calcium absorption from the intestinal tract by active vitamin D and uptake by bone. Conclusion Following surgery for hyperthyroidism, substantial improvement in BMD in patients with severe hypocalcemia can be anticipated with adequate calcium and vitamin D supplementation.