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By: Sam Chang, MD
Introduction
Renal stone disease (nephrolithiasis, kidney stones, or urinary lithiasis) is a
common disorder involving around 10 percent of the U.S. population. Although
many people spontaneously pass their stones—thus, not requiring any
intervention—prompt diagnosis as well as therapy, when indicated, are important
in preventing possible morbidities such as infection, bleeding, unrelenting
pain, or damage to the kidneys due obstruction. The term urinary obstruction
means blockage of urinary drainage.
Who Gets Kidney Stones?
Males tend to be more often affected with a 3:1 ratio compared to females. Stone
formation can occur at any age but is most common in the age range of 20 years
old to 50 years old. If you have one kidney stone, you are much more likely to
have another stone episode. It is estimated that the risk is 50 percent over the
next 10 years to have another stone attack and actually, this risk increases as
time goes on with that risk increasing up to 75 percent or higher. The
prevalence of nephrolithiasis is thought to be higher in certain geographical
areas. These geographical areas include desert, tropical zones, as well as
mountain-type climates. Currently, it is unclear why these areas tend to have
populations of people with a greater tendency toward stone formation. In the
U.S., the so-called stone belt involves a large portion of the southeastern U.S.
as well as portions of the western U.S.
Types of Kidney Stones
Most commonly, kidney stones have some form or type of calcium. In fact, more
than 70 percent of kidney stones have some type of calcium component. These may
be so-called calcium oxalate or calcium phosphate stones or some mixture of
these two types. Other types of kidney stones occur much less frequently. These
types include struvite stones, uric acid stones, cystine stones, miscellaneous
stones, and other types of calcium stones.
How Do Stones Occur?
Although in some cases, there is a known, well-defined mechanism, for many
people, it is unclear the exact way that their particular stone has formed.
Examples of well-defined mechanisms include the formation of cystine stones,
which are due to an inborn genetic error in amino-acid transport. Another
example would be calcium stones that are due to a high level of calcium in the
blood stream due to a disease entity called primary hyperparathyroidism. Another
example includes uric acid stones associated with gout, (the uric acid crystals
are deposited in joints) . To form a stone, an actual crystal has to form within
the urine. This solid crystal formation depends on many factors including
temperature, pH of the urine, as well as the amount of substances in the urine.
Depending on these factors, stones may or may not form.
Common Risk Factors
1) Dietary excesses including, but not commonly, too much calcium intake.
2) Medications such as antacids; protein supplements; Indinavir (for HIV);
acetazolamide, triamterene, thiazides (diuretics); and vitamins C and D,
3) Environmental factors such as dehydration.
What are Common Causes?
There are three common causes for kidney stones. They include:
* The most common cause of kidney stones is the kidneys produce urine that has
too much calcium—this is known as hypercalciuria. This may be due to absorption
of too much calcium from the intestines and the blood stream or it may be due to
the kidneys allowing too much calcium to be "leaked" into the urine. Regardless
of the mechanism, what happens is that there is too much calcium in the urine,
and as a result, a crystal forms. This crystal represents a kidney stone.
Another reason why urine may have too much calcium is, as stated previously,
hyperparathyroidism. The blood stream, due to the mechanisms of the parathyroid
gland, has a much higher than normal level of calcium within the blood stream.
Other less common causes of having too much calcium in the urine would be
certain malignancies and immobilization.
* The kidneys may actually allow too much of the substance called oxalate in the
urine. Oxalate is an important substance in the urine that contributes to the
formation of a stone when there is an overabundance.
* The kidneys may allow too much uric acid in the urine and as a result, uric
acid stone formation is much more likely.
What are Signs and Symptoms of Kidney Stones?
Symptomatic kidney stones have a variety of presenting symptoms, and often times
can be confused with other disease processes. The differential diagnosis would
include: muscular back pain, acute appendicitis, cholecystitis (inflamed
gallbladder), peptic ulcer disease, pancreatitis, pyelonephritis (inflammation
of the kidney), and diverticulitis (inflamed pouches in large intestine). All of
these disease entities must be carefully ruled out or considered when you are
also considering the diagnosis of a kidney stone. A classic kidney stone symptom
includes back pain that is sporadic in nature and that has a sudden onset. The
pain can also radiate to the groin area or testicles in men. Other symptoms are
nausea or vomiting, urinary frequency and burning, as well as blood in the
urine. Importantly, some patients may have no symptoms whatsoever and may still
have kidney stones. Often times, the pain of the kidney stones are due to
blockage and increased pressure of the urine.
How Do You Diagnose a Stone?
Initially, an accurate patient history is important. It is important to ask such
questions as the previous history of kidney stones, a history of urinary tract
infections, the amount of fluid intake the individual has had, previous
surgeries, and the use of certain medicines. Often times, patients who present
in the emergency room with a question of a stone attack need to have their urine
examined carefully. The vast majority of times, greater than 80 percent of
times, there is evidence of blood in the urine. Many times one cannot see the
blood in the urine and it is, in fact, microscopically found. In addition,
careful analysis of the urine can reveal evidence of small crystals as well as
evidence of possible associated urinary tract infection. Also, in an emergent
evaluation, often times radiological evaluation is necessary. Different forms of
radiological examination include an IVP, or intravenous pyelogram. This x-ray
involves giving an injection of a substance that can be seen on x-ray and that
is absorbed by the kidney. This x-ray shows an outline of the kidney and the
drainage of the kidney down into the bladder and will often times show an area
of blockage or the actual kidney stone. In certain places, instead of an IVP, a
CAT scan is performed, which can show evidence of a kidney stone in the kidney
or in the tube from the kidney down into the bladder.
After kidney stone disease has been verified, a more extensive evaluation is
necessary. It is important to remember that the analysis of the stone, or, in
other words, determining what type of stone a patient has, is essential in the
future treatment. Therefore, patients are given a strainer to strain their urine
in order to capture any fragments that they may have passed so they can be
examined .
Treatment of Urinary Nephrolithiasis
Spontaneous passage
Stone passage depends on a combination of mechanical factors, the two most
important being the size of the stone and the patient's anatomy. The vast
majority of stones smaller than 5.0 millimeters pass without any required
intervention, but patients may require pain medications and even
hospitalization. The larger the stone is, the less likely it is to pass
spontaneously. For patients who present with kidney stone pain, pain
medications, usually narcotics of some type via either an oral, intramuscular,
or intravenous route are often times necessary. In addition, vigorous
intravenous fluids are often given to increase urinary flow.
When Do You Have to be Hospitalized?
If you do not have a fever, have no evidence of urinary tract infection, are
comfortable on oral pain medications or no pain medications, you’re able to
tolerate liquids and/or food, and most important, you have a small enough stone
that may pass spontaneously, a trial of careful observation is often chosen. The
patient is given a period of time in which the stone will hopefully pass through
the urinary tract system and be voided out with the urinary stream.
Several key signs or symptoms that, however, prompt hospitalization include:
* fever
* inability to keep liquids down due to nausea and vomiting
* evidence of an obstructed single kidney (when patient has only one kidney)
* pain that is uncontrolled with oral pain medications
These indicators would be the most common reasons for hospitalization.
Treatment Options
Surgical intervention is the initial treatment of choice, if treatment is
necessary. Medical therapy is then often times important for prevention of
further stones; however, it can be used for treatment of certain stone types. To
immediately relieve obstruction of the urinary tract system caused by stones,
the urine can actually be diverted internally or externally. Internally, a
temporary small flexible tube or stent is placed, usually requiring an
anesthetic. No skin incisions are required and the patients void (urinate)
normally. Externally, a drainage tube can be placed via a small incision through
the back with the tube actually placed directly into the kidney and then drained
via this tube into a collection bag. The reasons for urinary diversion are to
decrease pain. By bypassing the obstruction, one gets pain relief.
There are different modalities to actually fragment or crush the kidney
stone—either in the kidney, in the tube going from the kidney to the bladder, or
right at the junction of the ureter and the bladder—depending upon the location
of the stone. The goal is to fragment or crush the stone small enough so that
the body can spontaneously pass these fragments or have a urologist remove the
fragments, depending upon the treatment choice that is taken.
Removal methods
These methods include ESWL (extracorporeal shock wave lithotripsy) ,
ureteroscopic stone extraction, percutaneous nephrolithotomy, and open surgical
stone extraction. Depending on the stone type; stone location; the patient’s
body size, previous operations, medical history, and patient preference; one of
these treatment choices is taken. ESWL is the “shock wave” therapy that involves
a water bath or special machine that sends shock waves to fragment the stone.
The stone then passes without further manipulation. Ureteroscopic stone
extraction utilizes special instruments that are used to visualize the bladder
and ureter. No incisions in the skin are necessary. This differs from the
percutaneous nephrolithotomy technique that also uses special instruments but
requires a skin incision and going straight into muscle, directly to the kidney.
Open surgical stone extraction requires a larger incision for visualization of
the kidney and collecting system.
Depending on stone type, certain medical interventions requiring medications is
also essential. For nearly any stone, adequate intake of fluids is essential,
and actually, increased fluid intake is often necessary and encouraged. At the
minimum, you want to drink enough fluids to produce at least two liters of urine
per day. For those patients who have too much calcium in the urine, certain
medications such as Thiazide and cellulose sodium phosphate and neutral sodium
phosphate (calcium-absorbing medications) can be used. Reduction in dietary
calcium intake is only recommended if dietary calcium is excessive. Decreased
salt intake is also often recommended.
If the patient has a uric acid stone, it is important that the pH of the urine
is modified. Medication such as sodium bicarbonate is used to decrease the
acidity of the urine and thus decrease the likelihood of stone formation—
specifically, uric acid stone formation. In some cases, a medication called
allopurinol is also used. Allopurinol decreases uric acid production. Therefore,
the less uric acid produced, the less likely there will be uric acid stones. For
cystine stones, treatment is similar to that of uric acid stones, but actually
requires even more aggressive fluid intake and more aggressive alkalinization of
the urine.
Conclusion
Kidney stones affect a significant portion of the U.S. population. Treatment for
these stones can vary depending on stone type, location, size, and number.
Prevention of future stones, however, is as important in patient outcome, and
like treatment, needs to be individualized for each patient.