Thyrotoxicosis and hungry bone syndrome--a cause of posttreatment hypocalcemia

We report a case of a 54 year old woman with a history of recurrent Graves' disease, treated previously by thyroidectomy and later by radioiodine, who subsequently presented with tetany. Laboratory results revealed a profound hypocalcemia (total calcium 1.00 mmol/L; ionized calcium 0.53 mmol/L) and hyperphosphatemia (2.66 mmol/L) with low levels of parathyroid hormone. Although the patient's symptoms resolved after 5 days of treatment, hypocalcemia and elevated serum levels of bone-specific alkaline phosphatase (ALP, EC 3.1.3.1) activity and skeletal muscle isoenzyme (CK-MM) creatine kinase (EC 2.7.3.2) activity persisted to her discharge, 3 weeks later. Attention is drawn to the recognition and management of recalcification tetany due to the "Hungry (for calcium) Bone Syndrome," a biochemical and hormonal disturbance of calcium homeostasis and bone metabolism in the posttherapy thyrotoxic patient with hypoparathyroidism. This condition can be monitored by the use of calcium profile investigations, including bone-specific ALP, in addition to routine laboratory tests of thyroid function.