Dipartimento di Scienze Mediche e, Chirurgiche, Policlinico Universitario, Via Giustiniani 2, 35120 Padova, Italy. Email: bruno.baggio{at}unipd.it
Sir,
A 55-year-old recurrent stone-forming woman was hospitalized in 1995 for renal colic due to the presence of a ureteral calculus, which at chemical evaluation was composed of calcium, oxalate and phosphate.
Routine biochemical screening showed normal renal function, normal plasma uric acid, and the presence of features typical of hyperparathyroidism such as hypercalcaemia, hypophosphataemia, increased levels of ionized calcium, increased urinary excretion of calcium and phosphate and increased plasma parathyroid hormone. The diagnosis of an adenoma affecting a single parathyroid gland was confirmed by ultrasound examination, thallium/technetium subtraction scintigraphy and histology after the surgical removal of the gland.
Surprisingly, the cyanidenitroprusside test, performed for routine biochemical evaluation of recurrent renal stone-forming patients, was positive for cystinuria. At first sight, the hypothesis might be advanced that the observed increase in urinary cystine excretion was indicative of a tubular defect secondary to hyperparathyroidism. A marked Fanconi-like aminoaciduria has been reported in one-third of patients with primary hyperparathyroidism, which usually disappears after correction of the primary disease [1]. This hypothesis was excluded, as urine chromatography aminoanalysis showed a selective excess of the basic amino acids cystine, lysine, arginine and ornithine. Moreover, plasma bicarbonate and chloride were normal, the ammonium chloride acidification test lowered urine pH to <5.5 and glycosuria was absent.
These biochemical features indicated that the patient was suffering from two diseases and two causes of renal stone formation, namely primary hyperparathyroidism and cystinuria. The first disease represents 7% of the causes of nephrolithiasis, while the latter is a well-known autosomal recessive genetic disease, responsible for 12% of renal calculi. The family evaluation revealed the presence of cystinuria also in the patient's brother, who was affected with recurrent nephrolithiasis as well, and in the two daughters, who were not renal stone formers. During the 7-year follow-up after surgical removal of the parathyroid adenoma, the patient did not experience recurrence of nephrolithiasis, suggesting that renal calculi formation was mainly due to hyperparathyroidism. This is the first observation of an association of primary hyperparathyroidism with cystinuria in a renal stone-forming patient.
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