Kidney stone

Kidney stones, also known as nephrolithiases, urolithiases or renal calculi, are solid accretions (crystals) of dissolved minerals in urine found inside the kidneys or ureters. They vary in size from as small as a grain of sand to as large as a golf ball. Kidney stones typically leave the body in the urine stream; if they grow relatively large before passing (on the order of millimeters), obstruction of a ureter and distention with urine can cause severe pain most commonly felt in the flank, lower abdomen and groin. Kidney stones are unrelated to gallstones.

Etiology

Conventional wisdom has held that consumption of too much calcium can aggravate the development of kidney stones, since the most common type of stone is calcium oxalate. However, strong evidence has accumulated demonstrating that low-calcium diets are associated with higher stone risk and vice-versa for the typical stone former.

Other examples of kidney stones include struvite (magnesium, ammonium and phosphate), uric acid, calcium phosphate, or cystine (found only in people suffering from cystinuria). The formation of struvite stones is associated with the presence of urease splitting bacteria (Klebsiella, Serratia, Proteus, Providencia species) which can split urea into ammonia, most commonly Proteus mirabilis.

Symptoms

Kidney stones are usually asymptomatic until they obstruct the flow of urine. Symptoms can include acute flank pain (renal colic), nausea and vomiting, restlessness, dull pain, hematuria, and possibly fever if infection is present. Acute renal colic is described as one of the worst types of pain that a patient can suffer. Note that the pain is generally due to the stone's presence in the ureter, and not—as is commonly believed—the urethra and lower genitals.

Some patients have no symptoms until their urine turns bloody—this may be the first symptom of a kidney stone. The amount of blood may not be sufficient to be seen, and thus the first warning can be microscopic hematuria, when red blood cells are found in the microscopic study of a urine sample, during a routine medical test.

Diagnosis & Investigation

Diagnosis is usually made on the basis of the location and severity of the pain, which is typically colic in nature (comes and goes in spasmodic waves). Radiological imaging is used to confirm the diagnosis and a number of other tests can be undertaken to help establish both the possible cause and consequences of the stone. Ultrasound imaging is also useful as it will give details about the presence of hydronephrosis (swelling of the kidney - suggesting the stone is blocking the outflow of urine). It will also show the 10% of stones that do not have enough calcium to be seen on x-rays (radio-opaque stones).

The relatively dense calcium renders these stones radio-opaque and they can be detected by a traditional X-ray of the abdomen that includes Kidneys, Ureters and Bladder—KUB. This may be followed by an IVP (Intravenous Pyelogram; IntraVenous Urogram (IVU) is the same test by another name) which requires about 50ml of a special dye to be injected into the bloodstream that goes straight to the kidneys and helps outline any stone on a repeated X-ray. These can also be detected by a Retrograde pyelogram. Computed tomography, a specialized X-ray, is by far the most accurate diagnostic test for the detection of kidney stones.

Investigations typically carried out include:

Microscopic study of urine, which may show proteins, red blood cells, pus cells, cellular casts and crystals.
Culture of a urine sample to exclude urine infection (either as a differential cause of the patient's pain, or secondary to the presence of a stone)
Blood tests: Full blood count for the presence of a raised white cell count (Neutrophilia) suggestive of infection, a check of renal function and if raised blood calcium blood levels (hypercalcaemia).
24 hour urine collection to measure total daily urinary calcium, oxalate and phiosphate.

Treatment

Stones less than 5 mm in size usually will pass spontaneously, with diclofenac usually providing effective pain management. However the majority of stones greater than 6 mm will require some form of intervention, especially so if the stone is stuck causing obstruction and infection of the urinary tract.

In many cases non-invasive Extracorporeal Shock Wave Lithotripsy may be used. Otherwise some form of invasive procedure is required; with approaches including retrograde ureteral, percutaneous nephrolithotomy or open surgery, and using laser, ultrasonic and mechanical (pneumatic, shock-wave) forms of energy to fragment stones.

A single study at the Mayo clinic has suggested that Lithotripsy may increase subsequent incidence of diabetes and hypertension, but it has not been felt warranted to change clinical practice at the clinic.

Secondary Prevention

Preventive strategies include dietary modifications and sometimes also taking drugs with the goal of reducing excretory load on the kidneys:

Drinking enough water to make 2 to 2.5 litres of urine per day.
A diet low in protein, nitrogen and sodium intake.
Restriction of oxalate-rich foods and maintaining an adequate intake of dietary calcium is recommended. There is no convincing evidence that calcium supplements increase the risk of stone formation.
Taking drugs such as thiazides, potassium citrate and allopurinol depending on the cause of stone formation.

Certain foods may increase the risk of stones: spinach, chocolate, peanuts, cocoa, tomato juice, grapefruit juice, apple juice, soda (acidic and contains phosphorus), all types of tea, and coffee (high levels of oxalate). In the United States, the South has the highest incidence of kidney stones, a region where sweet tea consumption is very common. Other drinks are associated with decreased risk of stones, including wine, lemonade and orange juice. Although it has been said that the diuretic effects of alcohol can result in dehydration which is important for kidney stones sufferers to avoid, there are no data demonstrating an effect of it to increase the prevalence of stones. It is important to recognize that one of the recognized medical therapies for prevention of stones is thiazides, a class of drugs usually thought of as diuretic. These drugs prevent stones through an effect independent of their diuretic properties: they reduce urinary calcium. Nonetheless, their diuretic property does not preclude their successful use as stone preventive. Caffeine does acutely increase urinary calcium excretion, however coffee, with its high oxalate content, has been known to cause stones in some patients and should be used in extreme moderation.

A high protein diet may partly be to blame. Protein from meat and other animal products is broken down into acids. The most available alkaline base to balance the acid from protein is calcium from the bones. The kidney filters the blood and stores the calcium particles which have bonded with the acids. When more meat or dairy is eaten, more calcium is found in the kidneys. Over time, and when not properly removed, these particles bind together to form stones. One of the simplest fixes is to moderate animal protein consumption.

Famous sufferers

In 271 or 270 BCE, the Greek Philosopher Epicurus died from a kidney stone blockage lasting a fortnight according to his successor Hermarchus and reported by his biographer Diogenes Laertius.

French Renaissance essayist Montaigne suffered from kidney stones. British statesman Samuel Pepys also suffered from kidney stones and was operated on, pre-anesthesia, to remove a large stone which he carried with him and used to try to persuade fellow sufferers to endure the painful surgery. His contemporary, John Wilkins, Bishop of Chester, could not face the prospect and died as a result.

Author Isaac Asimov suffered from kidney stones, and wrote about how his pain was treated with morphine, saying that he feared becoming addicted to morphine if he ever needed it again.

Astronauts often get kidney stones because of an increase in the amount of calcium in their blood due to a loss of bone density in zero gravity.

In his book A Year At the Movies, Mystery Science Theatre 3000 writer/performer Kevin Murphy describes his ordeal with a kidney stone: "Being gut-stabbed with a dirty spoon in a prison cafeteria is less painful."

Speaker of the House of Representatives, Dennis Hastert, has had a number of kidney stones. Hastert had to have kidney stone removal surgery.

On October 19, 2005, while working on the set of Boston Legal, Actor William Shatner was taken to the emergency room for lower back pain. He eventually passed a kidney stone, but recovered and soon returned to work. Shatner sold his kidney stone in 2006 for $75,000 to GoldenPalace.com. The money will go to a housing charity. ^*

Reggaeton artist Tito El Bambino briefly suffered from kidney stones.

Fictitious sufferers

In the sixth season episode of Seinfeld, titled "The Gymnast," Kramer suffers from a kidney stone that he descibes as "a stony mineral concretion, formed abnormally in the kidney. And this jagged shard of calcium pushes its way through the ureter into the bladder. It's forced out through the urine!" At the end of the episode, he passes the stone while in the washroom at a circus.

References and notes

External links

Urology Nephrology

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