Kidney Stones
Overview
In the United States, the lifetime prevalence of kidney stones is about 10%. The annual incidence is about 0.2%.
Males are more prone to suffer from kidney stones than females (2:1 ratio). Females tend to have recurrent stones secondary to infection. People who are at increased risk tend to be obese and have a sedentary lifestyle.
Key Points:
#1. Kidney stones are abnormal.
#2: It is a prevalent condition. Risk factors include: male sex, obesity, sedentary lifestyle.
Pathophysiology
Anatomy. Kidneys are bean-shaped organs that function to clear the toxic substances from the body and purifies blood that is being routed back again into the body to supply the organ systems. The kidneys are a size of about 4 to 5 inches in length and about 2 to 3 inches in width. The outermost layer of kidney is known as cortex and underneath the cortex is medulla that contains the pyramids, which are formed by the tubules that filters out the toxic substances from the blood. The portion of the cortex that extends between the renal pyramids is known as renal columns. In the center of the kidney there is a cavity known as the renal pelvis. On the whole the renal system includes kidneys, ureters, urinary bladder, and urethra.
Pathophysiology. Two basic mechanisms cause renal stones. One phenomenon is supersaturation of the urine by stone-forming constituents, including calcium and oxalates. A second phenomenon is renal tubular dame or dysfunction. Both can be caused by a reduction in the volume of the urine causing the urine to change from the normal pH to an acidic urine. This change may cause the precipitation of the salts and results in the formation of kidney stones. Another possible mechanism is an increase in the level of mineral leads to the development of kidney stones.
Key Points:
#1. The renal system consists of kidneys, ureters, urinary bladder and urethra.
#2. Two basic conditions cause formation of the kidney stones: supersaturation of the urine by stone-forming constituents and renal tubular damage.
Types of kidney stones
1. Calcium Stones: Calcium stones are formed when excess calcium combines with the other waste substances to form the stones. They constitute about 70% of the kidney stones. The different causes that lead to increased calcium concentration include:
A. Increased calcium in urine. Increased concentrations of calcium in urine can lead to the formation of the stones, which occur due to the following reasons.
a. Increased intestinal absorption. Increased intestinal absorption of calcium leads to higher concentrations of calcium in blood, which in turn leads to the increased levels of calcium in urine.
b. Increased chloride concentrations. Increase in the chloride concentrations can lead to the increased calcium retention. Since chloride is of negative charge and calcium is positive charge, this causes a pulling effect of the calcium that is to be excreted and increases the concentration of calcium in the urine.
c. Increased sodium concentrations. Increase in the level of sodium leads to increase in the levels of calcium in urine.
d. Clinical conditions. There are certain clinical conditions that cause increased levels of calcium in the urine, which includes cancers and sarcoidosis.
e. Drugs. There are some drugs that lead to the increased concentrations of calcium in the urine, which includes thyroid hormones, as well as diuretics.
B. Increased calcium in blood. High levels of calcium in blood occur due to the re-absorption of calcium from the bones. The causes are listed below:
a. Parathyroid glands. The increased activity of the parathyroid glands, which is also known as hyperparathyroidism results in the increased level of calcium in blood. The increased activity of the parathyroid glands results in the formation of stones in about 5% of the individual.
b. Renal tubular acidosis. This condition increases the level of calcium because of an imbalance of the acid and alkaline environment in the kidneys.
2. Uric Acid Stones: Uric acid stones are caused by the ingestion of a high purine diet and increased acidity of the urine. They are formed due to the high content of purine, which then result in the formation of the uric acid crystals. The high acidic environment of the urine results in the precipitation , or formation of uric acid stones. The different conditions that lead to the development of high levels of uric acid in blood include:
a. High protein diet.
b. Gout.
c. Fasting.
d. Chronic diarrhea.
e. Leukemia.
f. Multiple myeloma.
g. Lymphomas.
h. Chemotherapeutic drugs.
i. Diuretics.
k. Salicylates.
g. Lead toxicity.
3. Struvite Stones: These stones are also known as the magnesium, ammonium and phosphate stones and they occur after a urinary tract infection.
These stones are always formed due to the urinary tract infections. The bacteria causing the urinary tract infection causes the secretion of an enzyme that causes the urine to become highly acidic due to the increased levels of ammonia. The organisms that are involved in promoting the formation of this type of stone include Klebsiella, Pseudomonas, Serratia and staphylococci. Another interesting fact that needs to be shared here is that women have Struvite Stones twice as more than men.
4. Cystine Stones: These are the most uncommon stones and occur because of the development of a metabolic defect, which prevents the kidneys from reabsorbing the compounds. As a result, there is increased accumulation of cystine and this causes the formation of stones. These stones are caused due to the metabolic defect that prevents the reabsorption of cystine.
Key Point:
#1. The kidney stones are of four different types, which include calcium stones, uric acid stones, struvite stones, and cystine stones.
Symptoms
According to the different locations of the stone, the intensity and the severity of the symptoms are different.
1. Stones in kidney are usually asymptomatic. The reason that stones do not usually cause pain in the kidneys is due to the fact that they are settled in their location and do not move to cause any pain symptoms.
2. Stones in ureter can be rather painful. Most of the symptoms occur when the stone travels down from the kidney into the ureter. Ureter is a tube that channels the urine from the kidneys into the urinary bladder. The symptoms the individual experiences with the stone in the ureter are listed as follows.
a. Sudden sharp pain. With the stone in the ureter, the individual can experience sudden severe sharp pain in the back, which can also be experienced into the sides, groin or genitals. The pain is experienced because the contractions of the ureter are causing the stone to move.
b. Nausea and vomiting. The feeling of intense pain causes the individual to develop the feeling of nausea and vomiting.
c. Hematuria (blood in urine). This situation occurs when the stone is big and with the contractions of the ureter it moves and injures the walls of the ureter, which causes the blood to express out in the urine. Sometimes the blood is not visible in the urine and gets confirmed through the laboratory test.
d. Dysuria (pain on urination). There is severe pain on urination due to the stone in the ureter. The pain on urination also denotes the presence of infection.
e. Fever.
f. Decrease in appetite.
g. Constipation and diarrhea.
h. Increased sweating.
i. General malaise and lethargy.
3. Stones in urinary bladder will cause the same symptoms as described above.
Key Point:
#1. The symptoms of kidney stones include severe pain, nausea, vomiting, dysuria, fever, decrease in appetite, constipation and diarrhea, increased sweating, general malaise and lethargy.
Diagnosis
1. History and physical examination. The doctor takes the history in which he determines as to the area of the pain, development of fever, character of pain, pain on urination, increased fatigue, blood in urine, nausea and fatigue. The physician also palpates the area of the kidney and the patient can experience dramatic moving costovertebral angle tenderness due to the presence of a migratory stone.
2. Urine test. A urinalysis is done to evaluate for hematuria and infection. One can check the pH because acidic environment can precipitate the kidney stones. Eight five percent of patients have hematuria, the presence of blood in the urine. A urine culture can also be performed to determine the organisms present in the urine. Calcium, magnesium, phosphate, citrate are also checked in the urinalysis. A 24 hour urinalysis may be useful in patients with recurrent symptoms or a strong family history of kidney stones.
3. Blood test. In a completed blood count, an elevated white blood count suggests infection. Serum electrolytes, such as urea, nitrogen, creatinine, calcium, phosphate and uric acid, are done to assess renal function and metabolic causes of kidney stones. The blood tests are also done to determine the level of the parathyroid hormones as it can be the cause of the formation of the calcium stones.
4. Imaging tests. There are imaging tests performed to establish a definite diagnosis.
a. Plain abdominal radiograph is a good initial test to assess size, shape, location of urinary calculi. Calcium- containing stones, 85% of all upper urinary tract calculi, are radiopaque.
b. Ultrasound. In this test high frequency sound waves are focused on the area of kidney with the help of a probe and it then detects the presence of stones in the kidneys, as well as the stones in the ureter. The ultrasound cannot detect the presence of small stones <5 mm.
c. Intravenous pyelogram or IVP. In this technique, a dye is injected into the vein and the dye then gets excreted through the kidneys. This dye results in enhanced imaging by x-rays and also helps delineate the presence of the stones in the urinary system. Sometimes the dye causes severe allergic reaction, so it is administered with great care.
d. Retrograde pyelogram. In this procedure, the cystoscope is passed through the urethra into the urinary bladder and then into the ureter where the dye is being injected and x-rays are taken. The major benefit of injecting the dye this way is that there are no reactions and very good quality images can be taken to establish the diagnosis of kidney stones.
e. CT scans. CT scan is a very useful tool that helps determine the stones in the kidney with precise accuracy of location and size.
Key Point:
#1. The diagnosis of kidney stones includes history and physical examination, urinalysis, blood tests, and imaging tests,
Treatments
1. Infection without obstruction. Treat with empiric antibiotics to cover gram negative organism which are most common in the urinary tract.
2. Obstruction without infection is managed with hydration, analgesics (such as NSAIDS, non steroidal anti-inflammatory drugs), and antiemetics (such as metoclopramide). Drink plenty of water because it helps dilute the urine, as well as it just dissolves out the stone as well.
3. Neither obstruction nor infection present. With hydration and analgesics the stone should pass (if it is <5 mm in diameter).
When there is a combination of pain, infection, and obstruction the following are to be considered:
4. Extracorporeal Shockwave Lithotripsy is a noninvasive procedure in which the stones are being broken down to pieces with the shockwave. After the procedure is done, the patient is asked to go home and the stones that turn into gravel due to the shockwaves are excreted out. The shockwaves are generated through an ultrasound machine. It might be that the individual who is passing the stone fragments might experience some pain and discomfort. If the passage of small pieces of stone is causing discomfort, then the doctor just passes a catheter and pulls down the stone to prevent pain from occurring.
5. Percutaneous nephrolithotomy. This procedure is also known as PNL. This procedure is done to take out large stones that are unable to be broken by the (ESWL) Extracorporeal Shockwave Lithotripsy. This procedure is also performed on patients who are obese. In this procedure, the doctor just bores a hole from the back into the kidney and takes out the stone. The stones that are larger and are unable to be pulled are broken down with the pneumatic drills so that it can be pulled out easily. After this process, the patient stays in the hospital for about a week and the passage is kept open with a small tube, which is called the nephrostomy tube, which is left in the kidney so that the remaining stones can pass out.
6. Ureteroscopy. This procedure is done when the stone is present in the mid to lower part of the ureter. In this procedure the doctor passes the ureteroscope from the urethra into the urinary bladder, which then passes into the ureter and then the surgeon locates the stones and the stones are shattered and a tube is left in there for the small stones or gravel to pass out.
7. Surgery. Surgery is the last option if all of the above procedures fail.
Key Point:
#1. Treatment of kidney stones include: Hydration, analgesics, antiemetics, extracorporeal shockwave lithotripsy, percutaneous nephrolithotomy, ureteroscopy and surgery.
Complications of kidney stones
The possible complications of kidney stones include:
1. Severe pain.
2. Recurrent fevers.
3. Nausea and vomiting.
4. Dysuria (pain on urination).
5. Blockage of ureter.
6. Scarring and stricture formation of the ureter.
7. Hematuria (blood in urine).
8. Combination of obstruction and infection can lead to pyelonephritis, pyelonephrosis, urosepsis, or abscess formation.
Key Point: Warning symptoms of complications include recurrent fevers, nausea, vomiting, and dramatic abdominal pain suggestive of infection and obstruction.
Tips for patients suffering from kidney stones
1. Hydration. Drink lots and lots of water as this will help dissolve the stone and make its size smaller and thus it will be able to pass without much difficulty.
2. Analgesics. Do try to avoid narcotic analgesics as this can lead you into addiction.
3. Dietary modifications. Try to avoid calcium, magnesium, phosphate, uric acid, high protein diet etc. that are known to cause the formation of kidney stones.
4. Patience. Just know that you are going to continue to suffer from pain with the kidney stone until the stone passes out. So you have to be patient till the stone passes out.
5. Education. Get to know the status of your kidney stones as soon as possible. The recurrence rate for urinary calculi is 50% within 5 years. Seek immediate medical help if abdominal pain or blood in urine recurs.
Key Point: Increasing your fluid intake, modifying your diet, and timely follow-up with your doctor is essential to prevent recurrence of kidney stones.
References
http://hcd2.bupa.co.uk/fact_sheets/html/Kidney_stones.html
http://www.nephrologychannel.com/kidneystones/causes.shtml
http://www.nsbri.org/HumanPhysSpace/focus4/ep-kidney.html
http://www.mayoclinic.com/health/kidney-stones/DS00282/DSECTION=6
http://www.jci.org/cgi/content/full/115/10/2598
http://www.duj.com/KidneyStones.html
Copyright 2008-9, MD Kiosk
