Medullary Nephrocalcinosis

 

Nephrocalcinosis refers to increased calcium content of the kidneys. This term usually applies to a generalized increase in renal calcium content, as opposed to a localized increase that is observed in calcified renal infarct or caseating renal tuberculosis.   Patients with hypercalcemia develop renal function abnormalities. When no definite evidence of increased renal calcium exists, the term hypercalcemic nephropathy is more appropriate. The main renal effect of hypercalcemia is on tubular function. Impaired renal concentrating ability and resistance to vasopressin are the most common defects observed with hypercalcemia. Maximum diluting capacity remains unimpaired. This is accompanied with increased excretion of sodium, potassium, and magnesium (due to suppression of PTH). Its effects on phosphate excretion are complex. In experimental animals, hypercalcemia reduces phosphate excretion; conversely, in hypercalcemia due to breast cancer, it increases phosphate excretion. Metabolic alkalosis, other than that caused by hyperparathyroidism, frequently has been reported in patients with hypercalcemia. Increased renal acid excretion occurs with intravenous calcium infusions, whereas parathyroid hormone decreases hydrogen ion excretion, leading to a distal type of renal tubular acidosis (RTA). This opposing effect of hypercalcemia and parathyroid hormone has been used in the differential diagnosis because the concentration of chloride is higher and bicarbonate is lower when hyperparathyroidism is the cause of hypercalcemia. Causes ·         Primary hyperparathyroidism is the single most common cause of nephrocalcinosis in adults. ·         Distal RTA is the second most common cause of medullary nephrocalcinosis. ·         Other causes of nephrocalcinosis are hypervitaminosis D due to treatment of hypoparathyroidism or self-administration of vitamins and granulomatous diseases, such as sarcoidosis due to increased conversion of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol within the sarcoid granuloma. ·         Even oral phosphate supplements for hypophosphatemia may contribute to renal calcification, whose clinical implications can readily be seen in children with hypophosphatemic rickets; nephrocalcinosis is increasingly being recognized as the most common complication. ·         Long-term furosemide abuse can cause medullary nephrocalcinosis in adults, and the risk of developing of nephrocalcinosis seems to be correlated with the daily dose of furosemide. Thus long-term furosemide abuse should be suspected in adult patients when medullary nephrocalcinosis is incidentally detected by US or CT. ·         Therapy of X-linked hypophosphatemia is often associated with nephrocalcinosis. The development of nephrocalcinosis is associated with renal tubular acidosis in patients with X-linked hypophosphatemia. The long-term sequela of renal tubular acidosis in patients with X-linked hypophosphatemia is unknown. Whether alkali therapy in patients who develop renal tubular acidosis affects growth, metabolic bone disease, or the progression of nephrocalcinosis will require further investigation ·         Idiopathic hypercalciuria, one of the common metabolic diseases, also is a known cause of nephrocalcinosis. ·         Medullary sponge kidney is a common cause of medullary calcification in which calcium lies in ectatic collecting ducts rather than the renal substance. ·         Hypervitaminosis D due to treatment of hypoparathyroidism or self-administration of vitamins ·         Milk-alkali syndrome due to ingestion of milk or alkali for ulcer dyspepsia ·         Sarcoidosis due to increased conversion of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol within the sarcoid granuloma ·         Children with hypophosphatemic rickets, nephrocalcinosis increasingly being recognized as most common complication ·         Idiopathic hypercalciuria, one of the common metabolic diseases, also is known cause of nephrocalcinosis ·         Renal papillary necrosis associated with phenacetin-induced analgesic nephropathy is identified as calcified papillae rather than speckled pattern. ·         Rapidly progressive osteoporosis due to immobilization, menopause, senility, or steroids also may cause nephrocalcinosis ·         Hyperoxaluria, primary (familial) or secondary to increased intake of oxalates, enhanced absorption due to intestinal disease, or ingestion of ethylene glycol or methoxyflurane can induce medullary calcification   Most common presenting complaints are renal colic, hematuria, urinary tract infection, passage of urinary stones, polyuria, or incidental detection.