Medullary Nephrocalcinosis in Young Subjects with Gout

Objective: To describe the characteristics of young subjects with gout associated with medullary nephrocalcinosis. Methods: A computerized search in the ultrasonography database of Chang-Gung Memorial Hospital identified 78,576 reports of kidney ultrasonography from 1997 to 2006. Clinical and laboratory data of subjects who were younger than 40 years old and had medullary nephrocalcinosis were analyzed. Subjects were divided into gout/hyperuricemia and non-gout groups. Results: Five hundred and forty five reports kidney ultrasonography contained diagnosis of medullary nephrocalcinosis. Of these, 123 subjects were aged younger than 40 years old and were diagnosed with medullary nephrocalcinosis. The most common diseases associated with medullary nephrocalcinosis were idiopathic urolithiasis (38/123, 30.9%) followed by gout (35/123, 28.5%) and primary hyperparathyroidism (9/123, 7.3%). Male subjects constituted 86.0% (37/43) of subjects in the gout/hyperuricemia group. Hypertension and azotemia were noted in 40.0% and 60.0% of subjects with gouty arthritis, respectively. Proteinuria (36.1%) and hematuria (50.0%) were both common. Apart from medullary nephrocalcinosis, kidney shrinkage and irregular kidney contours noted by ultrasonography was demonstrated in 4 (9.3%) and 13 (30.2%) subjects, respectively. Of note, in gout/ hyperuricemia subjects with normal renal function, 7.1% already had small kidney size. Conclusion: Gout and asymptomatic hyperuricemia should be considered important diseases associated with medullary nephrocalcinosis. Markers of kidney damage, such as proteinuria or small kidney size, can be observed in many young gout subjects with medullary nephrocalcinosis. They should be treated with caution to avoid further deterioration of renal function.