Kidney stone disease
| Kidney stone disease | |
|---|---|
| Specialty | Urology, nephrology  |
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.
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. 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. Computed tomography, a specialized X-ray, is by far the most accurate diagnostic test for the detection of kidney stones. Another test is by IVP (Intravenous Pyelogram) which requires roughly about 50ml of a special dye to be injected into the bloodstream that goes straight to the kidneys. After x-rays are done, the stone is clearly visible on the x-ray.
Other examples of kidney stones include struvite (magnesium, ammonium and phosphate), uric acid, calcium phosphate, or cystine (the amino acid 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 idiopathic and 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 from. But there are also people who have no symptoms until their urine turns bloody—this may be the first symptom of a kidney stone.
Treatment
Stones less than 5 mm in size usually will pass spontaneously, with diclofenac usually proving 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.
Preventive strategies include dietary modifications with the goal of reducing excratory load on the kidneys. Dietary modifications include:
- 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.
More information
Kidney stones are unrelated to gallstones.
A high protein diet may partly to be 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 from the blood and stores the calcium particles which have bonded with the acids. The more meat is eaten the 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 simply avoid protein.
The 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.
The 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.
Certain foods may increase the risk of stones: spinach, chocolate, peanuts, and cocoa; tomato juice and grapefruit juice; soda (acidic and contains phosphorus). Other drinks are associated with decreased risk of stones, including wine, coffee, lemonade and orange juice. Although it has been said that the diuretic effects of coffee and alcohol can result in dehydration which is important for kidney stones sufferers to avoid, there are no data demonstrating an effect of either to increase the prevalence of stones. In fact, multiple studies have shown that alcohol, beer, and coffee drinkers are protected and have a lower incidence of stones. This protective effect is greater than the effect of simply drinking more fluid. It is important to recognize in this context 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. Similarly, the data have consistently shown protective effects of alcohol and coffee. Caffeine does acutely increase urinary calcium excretion, another reason why coffee has often been proscribed for stone formers, but the epidemiologic evidence fails to support coffee restriction as an important therapeutic manipulation.