Magnesium (Mg), the second most abundant intracellular cation of the human body, plays a crucial role in nerve and muscle function. Although a frequent electrolyte abnormality, hypomagnesaemia is one of the most underdiagnosed one, symptoms being present only when Mg levels decrease bellow 0.5 mmol/l, Among the various causes of Mg deficiency endocrine disorders are neither the most frequent nor the most studied. An exception is the implication of Mg in bone and calcium metabolism. Mg deficiency can interfere with the recovery after parathyroidectomy, or from vitamin D deficiency. We present the evolution of postsurgical parathyroidism in the case of a 43 years old woman who has suffered near-total thyroidectomy for Graves disease. She developed overt signs of tetany, with very low calcium values (1.6 mmol/l) and hyperphosphoremia (2.3 mmol/l). She received high calcium doses (34 g/day) associated with vitamin D but the improvement was only temporary and Ca values remained low. Although Mg values were only to the inferior limit of the normal (0.65 mmol/l) we have associated oral sustained preparations (300 mg of mg/day). The Mg supplementation helped to improve patients state, biologically (Ca=2.10 g/l) and clinically. The etiology of hypocalcaemia in the setting of hypomagnesaemia is multifactorial. Hypomagnesaemia has a suppressive effect on PTH secretion and induces PTH resistance by interfering with G protein activation, but in the case of PTH deficiency, the main feature seems to be vitamin D resistance. The correlation between low Mg and low vitamin D levels is not clearly established. Since our patient associated osteoporosis (T score −3.6), dietary calcium supplementation is also necessary to improve bone turnover. Although calcium remains the star of bone remodeling, Mg have also an important contribution. Concomitant Mg intake will prevent the Ca/Mg imbalance and improve bone mineralization.
28 Apr - 02 May 2007
European Society of Endocrinology