What is Medullary Sponge Kidney?
Medullary sponge kidney is a harmless abnormality present from birth, first identified back in 1939. Imagine the inner part of your kidney filled with many small cysts (sacs filled with fluid), ranging from the size of a tiny seed to a pea. The kidney would look like a sponge if you could see inside, hence the name.
This condition often affects both kidneys, but it can also just affect one. It’s present in both kidneys in 70% of cases and is relatively rare, affecting about 1 in 5,000 people. Most of the time, you wouldn’t even know you have it, as there are usually no symptoms. However, some people may experience blood in their urine, urinary tract infections, or kidney stones. It tends to become apparent when people are between 20 to 30 years old.
It’s important to tell the difference between a medullary sponge kidney and a condition called medullary nephrocalcinosis. Medullary sponge kidney is one of the common causes of medullary nephrocalcinosis, which is when calcium salts build up in the inner part of the kidney. Other conditions such as overactive parathyroid glands (hyperparathyroidism), a certain type of kidney disease known as renal tubular acidosis type I, taking too much vitamin D (hypervitaminosis D), a condition called milk-alkali syndrome, and a disease called sarcoidosis, can also cause medullary nephrocalcinosis.
What Causes Medullary Sponge Kidney?
The exact cause of Medullary Sponge Kidney, a condition where cysts form in the small tubes within the kidneys, is unknown. While the majority of instances occur randomly, some seem to be passed down through families, though no specific genetic cause has been identified. However, it is worth noting that around 5% of cases are hereditary. There is also an association between this kidney condition and Beckwith-Wiedemann syndrome, a growth disorder.
Some studies also suggest there might be a connection between a condition called hyperparathyroidism, which affects glands in the neck, and Medullary Sponge Kidney. Additionally, other conditions have been linked to it, including Wilms tumor, a kidney cancer found in children, horseshoe kidney, Rabson-Mendenhall syndrome, Cakut syndrome, polycystic kidney disease, and Caroli’s disease.
The occurrence of Medullary Sponge Kidney is similar across different races and ethnic groups. It has also been linked with hemihyperplasia, previously known as hemihypertrophy – a condition where one side of the body grows significantly more than the other side.
In some cases, mutations have been found in two specific genes associated with Medullary Sponge Kidney: the gene for the Glial cell-derived neurotrophic factor (GDNF), which regulates the growth of cells, and the gene for the Receptor Tyrosine Kinase (RET), which is involved in cell communication.
Risk Factors and Frequency for Medullary Sponge Kidney
Medullary sponge kidney is a condition that affects roughly 1 in every 5,000 people. However, for individuals suffering from kidney stones, the chances of having this disorder increase to 12% to 20%. Women tend to be slightly more impacted by this condition than men. The average age of diagnosis is 27 years, but cases have been reported in newborn babies as well. The rate of occurrence for medullary sponge kidney is about the same in the United States as it is worldwide.
Signs and Symptoms of Medullary Sponge Kidney
Medullary sponge kidney is a condition where the patient often does not experience symptoms. However, in cases where symptoms are present, they may include blood in the urine, kidney pain similar to the pain of kidney stones, fever, and painful urination. Some patients may experience noticeable blood in their urine. They could also be at risk for complications such as kidney stones, urinary tract infections and conditions related to excessive levels of calcium in the urine and acidic urine.
At times, patients report experiencing chronic kidney pain even in the absence of infection, stones, swelling of the kidneys or any obvious obstruction. We’re not quite sure why this happens, but it could be due to blockages in the ducts of the kidney from mineral deposits. Diagnosis is usually made through medical imaging, such as renal ultrasound and CT scans of the urinary system. Sometimes, these diagnoses are made via basic abdominal X-rays covering the kidneys, ureters, and bladder.
There are estimates that suggest that between 12% to 20% of all people who frequently form calcium stones could potentially have medullary sponge kidney. This probability is even higher in women and younger patients, where it can range from 20% to 30%. Roughly 25% of cases of medullary sponge kidney are associated with uneven body growth, or hemihypertrophy. Moreover, it’s reported that approximately 10% of patients with hemihypertrophy also have a medullary sponge kidney.
Testing for Medullary Sponge Kidney
In the case of medullary sponge kidney, a condition that often presents with repeated urinary tract infections or kidney stones, your doctor will first gather a detailed history of your health and family history to help guide the diagnosis.
Generally, physical symptoms may not be apparent in patients with medullary sponge kidney. One exception could be occasional blood in the urine, also known as hematuria.
A range of imaging tests can assist in confirming a medullary sponge kidney diagnosis. For example, a simple X-ray of the kidneys, ureters, and bladder (KUB) could potentially reveal some stone-like deposits, although this method is not the most dependable.
A kidney ultrasound might be performed to look for specific changes in the medullary pyramids of the kidneys, which are triangular tissue structures found inside each kidney. However, the accuracy of an ultrasound largely depends on the skill and experience of the technician performing it.
An intravenous urography test (IVU), which involves injecting dye into the veins to visualize the urinary system, can reveal a particular ‘paintbrush-like’ appearance within the kidneys’ tubes. However, this test is not commonly used these days.
A multidetector contrast CT scan, an advanced type of imaging technique, can provide much clearer images. It can reveal a distinctive pattern known as ‘papillary blush’ and may show parallel streaks of contrast dye going from the papilla (part of the kidney) to the medulla (the inner part of the kidney) which stay visible even in the later images.
This type of CT scan can also help detect complications related to medullary sponge kidney, such as hydronephrosis (swelling of a kidney due to build-up of urine), kidney stones (calculi), and kidney infection (pyelonephritis).
Treatment Options for Medullary Sponge Kidney
Treatment of Medullary sponge kidney, a rare kidney disorder, involves handling the complications associated with it.
If you have urinary tract infections (UTIs) due to Medullary sponge kidney, doctors usually recommend antibiotics and careful personal hygiene.
For calcium stones, which are a common problem in this condition, the general advice is to drink plenty of fluids – enough to produce two liters of urine per day. A diet with low sodium, normal levels of calcium, high levels of potassium, and low-to-normal protein may also be beneficial.
If you suffer from Medullary sponge kidney and frequently develop stones, your doctor may suggest a 24-hour urine test to understand your body chemistry better. This kind of kidney problem often comes with higher incidences of two conditions – hypercalciuria (excessive calcium in the urine) and hypocitraturia (low citrate levels in the urine). If these are identified in the urine test, they can be treated with thiazide diuretics for hypercalciuria and potassium citrate supplements for hypocitraturia.
Potassium citrate supplements can also help limit long-term bone loss, a complication sometimes linked with Medullary sponge kidney. This bone loss may be mainly due to elevated levels of calcium in the urine, though impaired acidification in the urine may also be a factor. There could also be a link with hyperparathyroidism, a condition where the parathyroid glands in the neck release too much parathyroid hormone, leading to high levels of calcium in the blood.
Generally, the stones in patients with Medullary sponge kidney are small and pass out of the body naturally. But, sometimes, surgical intervention, ureteroscopy (where a thin tube is passed up the urinary tract to visualize the stones), or lithotripsy (a treatment to break down stones) may be necessary. Patients with Medullary sponge kidney who develop calcium stones usually occur around twice as often as other people who form calcium stones.
Some patients may also have a condition called distal type renal tubular acidosis (RTA), which means their kidneys fail to effectively remove acids from the blood into the urine. This condition can also lead to low citrate levels in the urine and can be treated with potassium citrate supplements. The dosage of these supplements must be adjusted to reach an optimal level of citrate in the urine (usually more than 500 mg in 24 hours), and to achieve a urinary pH level around 6.5, if possible. Urinary pH above 7.2 to 7.5 should be avoided to prevent the production of calcium phosphate stones. Regular monitoring of potassium levels in the blood is also necessary to prevent excessive levels of potassium, also known as hyperkalemia.
What else can Medullary Sponge Kidney be?
Medullary Sponge Kidney is a condition that can cause a buildup of calcium deposits in the kidneys, known as medullary nephrocalcinosis. However, other conditions can also lead to these calcium deposits, including:
- Hyperparathyroidism (an overactive parathyroid gland)
- Hypervitaminosis D (excessive Vitamin D)
- Milk-alkali syndrome (a condition caused by consuming too much calcium and alkali)
- Other conditions causing an extra high calcium level in the body or urine
- Papillary necrosis (damage to the kidney’s filtering system, often due to long-term painkiller abuse)
For instance, if a person has a history of excessive painkiller use, it might suggest that papillary necrosis is the cause of the calcium buildup rather than Medullary Sponge Kidney.
What to expect with Medullary Sponge Kidney
Medullary Sponge Kidney (a kidney condition) is generally not harmful. However, about 10% of patients with this condition may eventually experience kidney failure. Most people with this condition maintain normal kidney function throughout their lives. It is believed that kidney failure can occur due to repeated severe infections and the formation of large amounts of kidney stones.
A small number of patients with Medullary Sponge Kidney might experience chronic, intense pain. These patients tend to generate many more kidney stones than other patients with the same condition, averaging around 3.1 stones per patient each year. They often require multiple hospital stays for pain management. This indicates that a 24-hour urine test and proactive treatment aimed at preventing the formation of kidney stones could be particularly useful for this group of patients.
Possible Complications When Diagnosed with Medullary Sponge Kidney
A key problem related to medullary sponge kidney is recurrent kidney stones, which frequently cause intense kidney pain, often with blood in the urine. Kidney stones can also cause urinary tract infections and blockages.
Common Issues:
- Recurrent kidney stones
- Intense kidney pain
- Blood in the urine
- Urinary tract infections
- Blockage in the urinary tract
