22-27: Medullary Sponge Kidney

This disease is a relatively common and benign disorder that is present at birth and not usually diagnosed until the fourth or fifth decade. It can be caused by autosomal dominant mutations in the MCKD1 or MCKD2 genes on chromosomes 1 and 16, respectively. Kidneys have a marked irregular enlargement of the medullary and interpapillary collecting ducts. This is associated with medullary cysts that are diffuse, giving a “Swiss cheese” appearance in these regions.

Medullary sponge kidney may present with gross or microscopic hematuria, recurrent urinary tract infections, or nephrolithiasis. Common abnormalities are a decreased urinary concentrating ability and nephrocalcinosis; less common is incomplete type 1 distal renal tubular acidosis. The diagnosis can be made by CT, which shows cystic dilatation of the distal collecting tubules with a striated appearance, and calcifications in the renal collecting system.

There is no known therapy. Adequate fluid intake (2 L/day) helps prevent stone formation. If hypercalciuria is present, thiazide diuretics are recommended because they decrease calcium excretion. Alkali therapy is recommended if renal tubular acidosis is present.

Renal function is well maintained unless there are complications from recurrent urinary tract infections and nephrolithiasis.