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Severe Hypocalcaemia with Elevated PTH and Normal Vitamin D: A Diagnostic Pitfall due to Chronic Negative Calcium
1Private practice, Jaén, Spain.
Introduction:
Secondary hyperparathyroidism is usually associated with chronic kidney disease or vitamin D deficiency.
Case Description:
A 62-year-old man with severe osteoporosis presented with persistent hypocalcaemia and markedly elevated parathyroid hormone levels. Renal function, phosphate and vitamin D levels were normal. Extensive investigations excluded common causes. Twenty-four-hour urinary calcium excretion was profoundly reduced, indicating a chronic negative calcium balance. Dietary assessment revealed a strict vegan diet with low calcium intake and reduced bioavailability. Treatment with calcium citrate and calcitriol normalised serum calcium and reduced PTH levels.
Conclusion:
A chronic negative calcium balance is an under-recognised cause of secondary hyperparathyroidism. Measurement of urinary calcium is a key diagnostic tool in these patients.
Learning Points:
Secondary hyperparathyroidism may occur despite normal vitamin D and phosphate levels.Very low urinary calcium excretion is a key diagnostic clue in hypocalcaemia with elevated parathyroid hormone.A chronic negative calcium balance should be considered in patients with restrictive diets such as veganism.
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