Medullary Sponge Kidney: The Essential 101

This rare disease is often associated with not-so-rare complications

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Before I go about elucidating the details of medullary sponge kidney, let me briefly review the architecture of a normal human kidney.  That little bit of anatomical understanding is important to understand what is medullary sponge kidney or MSK.

As we know, the kidney is the body's excretory organ, where toxins are filtered out of the blood and into the urine.  Blood flows into the kidney through its main blood vessel (called the renal artery) which then subdivides into smaller and smaller capillaries.

 Such capillaries eventually lead in to the kidneys' filters called the glomeruli. Once filtration occurs here, fluid that will eventually form urine, enters in to what we call, tubules. 

By the way, the outer part of the kidney where most of these filters are present is called cortex, and the inner part where the final urine drains into the ureter is called the medulla (pictures to help you understand my rambling description here and here). 

Why am I giving you this crash course in renal anatomy?  Well, like it or not, understanding the microscopic architecture of the kidney is essential to understanding what is MSK.

SO WHAT IS MEDULLARY SPONGE KIDNEY (MSK)? 

Medullary sponge kidney is a congenital defect, and therefore present by birth.  In the affected person, the renal tubules in the medulla (or the inner part of the kidney, and hence the name) have an abnormal dilated appearance. The most common abnormality seen is the presence of cysts, or dilatations.Why these cysts form is not well understood.

WHAT ARE THE SYMPTOMS OF MEDULLARY SPONGE KIDNEY?

Even though MSK is present since birth in most patients, it might not make its presence felt until the patient is in their 20s. In fact, the diagnosis is usually discovered incidentally based off on the complications that are typically seen in medullary sponge kidney.

Therefore the symptoms of medullary sponge kidney are essentially the symptoms related to the complications of medullary sponge kidney. These could be:

  • Flank pain, sometimes because of kidney stones is a common complication
  • Repeated urinary tract infections
  • Blood in the urine, often related to UTIs or stones 

DOES MEDULLARY SPONGE KIDNEY LEAD TO KIDNEY FAILURE?

The short answer is, usually no (although this is still being investigated).  Most patients with medullary sponge kidney should not see a long-term higher risk of developing kidney failure any more than the average population.  This is an essential differentiating finding from polycystic kidney disease where the chances of kidney failure are typically high. Hence, although both conditions are associated with cysts in the kidney, the outcomes are markedly different. Which usually leads me to reiterate to my patients that cysts in the kidney do not always equate with a diagnosis of polycystic kidney disease, and therefore may not be as concerning.

 A good nephrologist should be able to differentiate between these entities pretty easily.

HOW IS MEDULLARY SPONGE KIDNEY DIAGNOSED? 

Once clinical suspicion has been raised, medullary sponge kidney is often diagnosed using a combination of imaging tests. These could include intravenous pyelogram (a type of special X-ray of the kidneys. The cysts in the MSK patient light up in a very characteristic way), CT scans, etc. 

WHAT IS THE TREATMENT FOR MEDULLARY SPONGE KIDNEY?

Since there is usually no significant higher risk of developing kidney failure in patients with medullary sponge kidney, the treatment really focuses on treatment of its complications.  Hence urinary tract infections and kidney stones are treated just like they would be in any other patient.  However, given the high risk of development of these complications in people with known medullary sponge kidney, prevention is also heavily focused on.  Hence dietary modifications required to reduce the risk of kidney stones (including high fluid intake and low sodium intake for instance) are often emphasized.

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