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RESEARCH PRODUCT

A case of hypocalcemia

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Hypocalcemia is a common disorder in the elderly, affecting 10% of the elderly population as a whole, 18% of those in hospital and 36% of those in long-term care [1, 2]. Many conditions can lead to hypocalcemia in adults young and old, e.g. primary hypoparathyroidism, chronic renal failure, gastrointestinal diseases (such as celiac disease or Crohn’s disease), drugs (particularly diuretics, bisphosphonates and antiepileptics), acute pancreatitis and thyroid surgery. Rare causes of hypocalcemia include isolated vitamin 1.25(OH)D3 deficiency or vitamin 1.25(OH)D3 resistance. Another, often neglected cause of hypocalcemia relating to functional parathyroid deficiency is hypomagnesemia. Magnesium and parathyroid hormone (PTH) are closely related, since the latter promotes magnesium reabsorption in the kidney, while mild hypomagnesemia (Mg [ 1.2 mg/dl) induces PTH secretion via a protein called CaSR (G protein) expressed particularly by the parathyroid glands. On the other hand, if blood magnesium levels drop below 1.2 mg/dl, the alpha subunit of the G protein is activated, and this leads to a decline in PTH secretion. This process is called a ‘‘paradoxical block’’ [3]. We report on a case of severe hypocalcemia in a 76-year old woman with hypomagnesemia and normal PTH levels. She was hospitalized at the Geriatric Department of the University of Padua for biliary colic: on admission the calcium level was 4.0 mg/dl. Cardiovascular examination showed a normal jugular venous pressure and normal heart sounds, with no murmurs or pericardial friction rub. Respiratory examination identified some crackling, compatible with mild cardiac failure, probably emphasized by the patient’s hypocalcemic state. Abdominal examination revealed nothing of note, with no Murphy or Blumberg signs. The patient was also negative for Trousseau’s and Chvostek’s signs. An electrocardiogram obtained on admission showed chronic atrial fibrillation with a mean rate of 78 bpm and an abnormal QTc interval (520 ms), with a severe risk of torsades de pointes. The patient had undergone total hip replacement for coxarthrosis in 2008, and had been on anticoagulant therapy for chronic atrial fibrillation since 2008. Her medical history was negative for any use of hypocalcemia-inducing medication (e.g. diuretics or bisphosphonates). Dietary assessment based on a modified version of the diet history questionnaire [4] indicated a low calorie intake (about 943 kcal), with a daily intake of 600 mg of calcium, 130 mg of magnesium and 54 IU of vitamin D3. After several episodes of lower back pain, she had undergone a computed imaging (CT scan) of the spine in 2006, which revealed osteopenia and major signs of arthrosis. Given the radiological evidence of osteopenia, she also had performed a DEXA (the T score was 2 for the lumbar spine and 1 for the total hip) and lumbosacral spine X-ray study with morphometry, which ruled out any collapse of the vertebrae. As shown in Table 1, on admission the patient had severe hypocalcemia (total calcium 4.0 mg/dl; free calcium 2.00 mg/dl), mild hyperphosphatemia, hypocalciuria and hypophosphaturia, with severe hypomagnesemia (1.4 mg/ dl), low vitamin 25(OH)D3 (\4 ng/ml) and normal PTH levels (60 ng/l). N. Veronese F. Bolzetta M. Mosele E. Manzato G. Sergi Department of Medical and Surgical Sciences, Division of Geriatrics, University of Padova, Via Giustiniani 2, 35128 Padova, Italy