From the Guidelines
Medullary sponge kidney (MSK) is a congenital disorder that predisposes individuals to kidney stones due to the cystic dilation of the collecting ducts in the renal medulla, which creates an ideal environment for crystal formation and concentration of stone-forming substances. This condition is characterized by the trapping of urine in the dilated collecting ducts, allowing it to stagnate and become concentrated, increasing the concentration of stone-forming substances like calcium, oxalate, and phosphate 1. The cystic structures themselves can serve as nucleation sites for crystals, and the altered anatomy disrupts normal urinary flow, preventing small crystals from being flushed out before they grow into stones. Most patients with MSK develop recurrent kidney stones, typically calcium-based, and may experience symptoms like flank pain, hematuria, and urinary tract infections. Management focuses on preventing stone formation through increased fluid intake, with a goal of at least 2.5 liters of urine daily, as recommended by the American Urological Association 1. Dietary modifications, such as limiting sodium intake and consuming 1,000-1,200 mg per day of dietary calcium, can also help reduce the risk of stone formation 1. Additionally, medications like thiazide diuretics may be used to reduce urinary calcium excretion, as recommended by the American College of Physicians 1. Some key points to consider in the management of MSK include:
- Increased fluid intake to achieve a urine volume of at least 2.5 liters daily
- Dietary modifications to reduce stone-forming substances, such as limiting sodium intake and consuming adequate dietary calcium
- Medications like thiazide diuretics to reduce urinary calcium excretion
- Avoiding supplemental calcium, which may be associated with an increased risk of stone formation 1. It is essential to note that the management of MSK should be individualized, taking into account the patient's specific needs and risk factors, and that a comprehensive approach that includes lifestyle modifications and medical therapy can help reduce the risk of recurrent kidney stones.
From the Research
Definition and Characteristics of Medullary Sponge Kidney
- Medullary Sponge Kidney (MSK) is a rare congenital malformation of the distal nephron where cystic dilatation is appreciable in the collecting ducts and renal papillae 2.
- MSK is generally considered a sporadic disorder, but an apparently autosomal dominant inheritance has also been observed 3.
- The disease is characterized by abnormalities in both the lower and the upper nephron and is often associated with urinary tract developmental anomalies 3.
Predisposition to Kidney Stones
- MSK predisposes people to kidney stones due to a defective distal acidification, which is followed by a chain of events including defective bone mineralization, hypercalciuria, hypocitraturia, and stone formation 3.
- The disease can lead to nephrocalcinosis and recurrent renal stones, as well as other signs such as renal acidification and concentration defects, and pre-calyceal duct ectasias 3.
- Patients with MSK are at risk of developing an obstructive nephropathy due to recurrent stone formation and passage 4.
Diagnosis and Treatment
- Diagnosis of MSK can be made using intra-venous urogram (IVU), endoscopy, and Multi-detector computed tomography (MDCT) 2.
- Treatment options for MSK include non-invasive treatments such as drug therapy, diet, and extracorporeal shock wave lithotripsy, as well as invasive therapies such as percutaneous nephrolithotomy, ureteroscopy, and surgery 5.
- The aim of treatment is to control stone formation by stabilizing urinary pH, and to remove symptomatic kidney stones using methods such as lithotripsy or surgical intervention 2.