A Problem-Solving in a Case of Medullary Nephrocalcinosis

Abstract

Medullary Nephrocalcinosis (MNC) is defined as calcium deposition in tubular basement membrane and interstitium of the kidney medulla. It is 20 times more common than cortical one. In this case report, we present a 12-year-boy who presented with persistent nocturnal enuresis for 8 years. Physical examination and routine tests were normal except for microscopic hematuria. Renal ultrasound showed extensive MNC. Twenty-four-hour urine collection revealed normal mineral metabolic screen with low urinary excretion of calcium, phosphorous, magnesium and uric acid yet high for oxalates. Hence, and based on the above-mentioned data, certain metabolic disorders were ruled out: 1) hyperparathyroidism, 2) excessive intake of vitamin D, 3) hypercalcemia, 4) hypercalciuria, 5) hyperuricemia, 6) hyperuricosuria, 7) hypocitraturia, 8) cystinuria, 9) lysinuria and 10) distal renal tubular acidosis were ruled out. Subsequently, urine testing showed high concentration of glycolate with low glycerate and 4-hydroxy-2-oxoglutarates establishing diagnosis of type 1 primary hyperoxaluria (PH I). Further confirmatory tests included: 1) kidney biopsy which showed typical crystals deposition, 2) liver biopsy that confirmed deficiency of the liver-specific peroxisomal enzyme alanine: glyoxylate aminotransferase (AGXT), and 3) full gene analysis that confirmed gene mutation. In conclusion, our case report provides practical algorithm for establishing diagnosis in MNC which is not renal-limited and its prognosis depends upon the underlying etiology.