A case of magnesium deficiency associated with insufficient parathyroid hormone action and severe osteoporosis.

The relationship between osteoporosis and magnesium (Mg) deficiency is still controversial. Here we report a case of an 82-year-old woman with a giant adenomatous goiter and severe osteoporosis with multiple vertebral fractures, whose clinical course indicated that her osteoporosis was probably due to Mg deficiency. She visited our hospital for treatments of tetany. Laboratory data showed the existence of hypomagnesemia, hypocalcemia, hypokalemia, vitamin D deficiency, and slightly elevated intact PTH. Intravenous administration of Mg not only improved these electrolyte abnormalities but also increased serum levels of intact PTH, bone formation markers, 1,25-dihydroxyvitamin D, as well as bone resorption markers in the urine, and lowered urinary phosphate reabsorption. Hypomagnesemia on admission seemed to arise from long-lasting poor food intake and malnutrition, because it improved after the disappearance of dysphagia with a goiter resection. After the operation, BMD values at the lumbar spine and femoral neck obviously increased during 6 months of Mg supplementation without any specific therapies for osteoporosis. Mg deficiency in this case seemed to cause impaired secretion of PTH from the parathyroid and the refractoriness of bone and kidney to the hormone, which led to the suppression of both bone remodeling and renal vitamin D production. These processes were probably linked to her severe osteoporosis, which was reversed by Mg supplementation.