Endocrine Aspect of Nephrolithiasis- An Overview

Introduction:

Nephrolithiasis or urolithiasis, also known as kidney stones, is a common condition affecting a large population. The condition is prevalent in both men and women, and the chances of developing kidney stones increase with age. The most common cause of kidney stone formation is increased calcium concentration in the urine due to reabsorption. This mechanism is directly and inadvertently affected by hyperfunctioning of the parathyroid glands. Therefore, it is safe to say that endocrine dysfunction (of parathyroid glands) can lead to nephrolithiasis.

What Is Nephrolithiasis?

Nephrolithiasis, also known as kidney stones or urolithiasis, is a condition characterized by forming a small solid piece of material known as calculus in the kidney or the urinary tract. A hard deposit forms in the kidney and often causes pain. A small kidney stone usually does not cause any significant issues; however, if the stone grows bigger (more than 5 mm), it can block the ureters (tube connecting kidneys to the urinary bladder) and cause multiple health issues. Nephrolithiasis occurs due to genetic and environmental factors. Nephrolithiasis is a common condition affecting both men and women. Approximately five percent of women and ten percent of men develop kidney stones by the age of seventy. Nephrolithiasis is a recurrent disorder, and it can recur at any age.

What Causes Nephrolithiasis?

The primary function of the kidneys is to clean the blood from all impurities and filter it. This process of purification can ultimately lead to the formation of renal calculi or kidney stones. If there is an excess amount of any impurity in the blood (this impurity can be calcium, uric acid, cystine, etc.), the kidneys will try to filter it, and eventually, this impurity will get collected, leading to the formation of kidney stones. The urine will become concentrated with these substances, and ultimately small calculi or stones will form and get collected inside the kidneys.

What Are the Risk Factors for Nephrolithiasis?

The risk factors of nephrolithiasis are primarily divided into three categories: Non-dietary, dietary, and urinary.

• Non-Dietary: The non-dietary risk factors for nephrolithiasis include:

• Dietary: The dietary factors leading to nephrolithiasis include:

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• Urinary: Abnormal concentrations of certain substances in the urine have been found to be a risk factor for the development of nephrolithiasis. These include:

What Are the Types of Nephrolithiasis?

There are four types of nephrolithiasis:

1. Calcium Stones: These are the most common form of kidney stones and contribute to about 90 % of all kidney stones.

2. Uric Acid Stones: They are associated with people who have a history of gout.

3. Cystine Stones: They occur hereditarily (a medical condition genetically transferred from parents to their children).

4. Struvite Stones: This type mainly occurs in women with urinary tract infections.

What Are the Symptoms of Nephrolithiasis?

The general symptoms of nephrolithiasis are:

• Abdominal pain.

• Back pain.

• Pain in the pelvic region and groins.

• Nausea and vomiting.

• Difficulty in urination.

• Pain in urination.

• Blood in the urine.

• Excessive urination during the night.

• Abnormal color of urine.

• Fever and chills.

• Increased frequency of urination throughout the day.

What Is the Endocrine Aspect of Nephrolithiasis?

• The most significant endocrine aspect of nephrolithiasis is the connection between the formation of kidney stones and hyperparathyroidism. The most common type of kidney stones has been reported to be calcium kidney stones, and they constitute almost 90 % of all kidney stones. These calcium kidney stones are formed due to an increased concentration of calcium in the urine. In addition, this increase in urine calcium concentration frequently occurs due to hyperparathyroidism.

• Hyperparathyroidism is an uncommon endocrine disorder characterized by a reduction in the production of the parathyroid hormone (PTH) in the body. The parathyroid hormone plays a key role in regulating and maintaining a balance of calcium and phosphorus in the body. Due to the reduced amount of PTH in the body, the calcium level in the blood becomes abnormally low, and the phosphorus level increases. The most common cause of hyperparathyroidism is a tumor of one of the parathyroid glands.

• The CaSR (calcium-sensing receptor) gene is responsible for the formation of the CaSR protein which is a protein found on the surface of the cells of the parathyroid glands and the kidneys. The calcium molecules attach themselves to the CaSR protein, which in turn enables the protein to regulate calcium in the blood. For the activation of the CaSR protein, the level of calcium in blood should be a lot higher than what is considered normal; therefore, in the case of hyperparathyroidism, the CaSR (calcium-sensing receptor) protein becomes less sensitive to calcium.

• Higher parathyroid hormone from the parathyroid gland instructs the kidney to absorb calcium back from the urine. At the same time, PTH also activates vitamin D. So, there is an increase in the levels of calcium, PTH, and calcitriol (activated form of vitamin D) in the blood. Higher levels of PTH cause higher absorption of calcium from the urine. Simultaneously, calcium and calcitriol also work on CaSR in the kidneys to decrease calcium reabsorption from urine. But eventually, CaSR activation by calcium and calcitriol outweighs the parathyroid hormone effect, and more calcium appears in the urine. This excess urine reabsorption leads to the formation of calcium stones in the kidneys.

How Are People With Nephrolithiasis Diagnosed and Treated?

The diagnosis of nephrolithiasis is made by means of radiological evaluation to determine the location and size of the kidney stones, renal ultrasound, blood tests, and urine tests. The treatment of nephrolithiasis includes the removal of all the risk factors that could be contributing to the condition and symptomatic relief with the help of drugs like painkillers, antibiotics, etc. Along with surgical removal of the stone if the stone is too big to pass on its own.

Conclusion:

Nephrolithiasis is a prevalent condition affecting the kidneys. It is characterized by the formation of small calculi in the kidneys or the urinary tract. The symptoms of the condition usually involve pain in the abdomen, pelvic region, and back. Along with frequent, painful urination and urinary tract infections, etc., the formation of nephrolithiasis is often associated with hyperparathyroidism because of the effect of PTH on calcium and phosphorus metabolism and regulation in the body. Hyperparathyroidism causes calcium reabsorption from the urine leading to kidney stone formation. The prognosis of nephrolithiasis is good, and the condition is fairly stable and manageable with the help of drugs and surgery.