During the last century, primary hyperparathyroidism (PHPT) passed from the category of rare severe diseases to a common endocrine disorder with a prevalence of mild forms. Over the last 10—20 years, widespread screening for osteoporosis has led to the «new era» in diagnosis of PHPT when patients are diagnosed at the stage of an isolated elevated parathyroid hormone with stable normal serum calcium levels and the absence of secondary causes of hyperparathyroidism. This phenomenon was called normocalcemic primary hyperparathyroidism (nPHPT); according to the literature data, its prevalence varies from 0.4 to 16.7% due to the lack of unified diagnostic criteria. The clinical picture and natural history of the disease are poorly explored, and it is still unclear if nPHPT is a separate disease entity or if it is an early stage of hypercalcemic PHPT. A number of studies have shown that complications of nPHPT (osteoporosis and urolithiasis) are similar to those of the symptomatic form of PHPT despite stable normocalcemia. However, these patients were often referred to specialized metabolic centers due to a decrease in the bone mass or nephrolithiasis, therefore the rate of complications in them may be overestimated. There are also controversial data on an increased risk of cardiovascular diseases due to metabolic disorders in this pathology. As a new clinical nosology, normocalcemic PHPT was first officially recognized at the Third International Workshop on Management of Asymptomatic PHPT in 2008, but there have been yet no common recommendations for its treatment. Some studies have shown a response to medical therapy and improved indicators of bone mineral density after parathyroidectomy in these patients. According to the experts of the Fourth International Workshop in 2014, nPHPT remains one of the key topics for further research.

Aim. To assess the incidence of kidney stone disease and to identify its clinical course in patients with primary hyperparathyroidism. Methods. 48 medical records of patients hospitalized with primary hyperparathyroidism were retrospectively analyzed. The average age of the patients was 57 [53; 61] years. The medical history, complaints upon admission, the clinical presentation, the results of laboratory test and instrumental examination were studied in evaluating the medical records. The patients were divided into the group with nephrolithiasis (n=33) and the group without nephrolithiasis (n=15). The differences between the two groups were tested for statistical significance by the MannWhitney U test. Results. Among patients with primary hyperparathyroidism, nephrolithiasis was detected in 69% of patients, of which 90% were women in the postmenopausal period. The course of the kidney stone disease in these patients was characterized by frequent recurrence with a predominance of bilateral renal impairment (62%). The duration of nephrolithiasis before the diagnosis of primary hyperparathyroidism was 6 [1; 19] years, and this complication was often the first manifestation of the disease. According to the instrumental examination of kidney in patients with nephrolithiasis, small stones up to 5 mm in diameter were detected in 42% of cases, asymptomatic kidney stones in 15% of cases. A severe complication of primary hyperparathyroidism staghorn calculi were found in 2 (10%) patients. The patients in the group with nephrolithiasis showed higher serum calcium (p=0.022) and parathyroid hormone (p=0.007) levels compared with patients in the group without nephrolithiasis. Conclusion. Nephrolithiasis is a common complication of primary hyperparathyroidism; the presence of nephrolithiasis is associated with more significant changes in calcium and phosphate metabolism and is also characterized by a frequent asymptomatic course, thus requiring attention of specialists to this type of complications in primary hyperparathyroidism.