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Preface and Contents

Stone Disease

Introduction, Types and Risk factors

Stone disease is a very common urological disease. Kidney stones can cause the most unbearable pain, but sometimes kidney stones can exist silently without any symptom. Stone disease can cause urinary tract infection and can damage the kidney if not treated adequately. Once a stone occurs, its recurrence is common. So understanding, prevention and care of stone disease is essential.

What is a kidney stone?

A kidney stone is a hard crystal mass formed within the kidney or urinary tract. Increased concentration of crystals or small particles of calcium, oxalate, urate, or phosphate in urine is responsible for stone formation. Millions of crystals of these substances in urine aggregate, gradually increase in size, and after a long period of time, form a stone.

Normally, urine contains substances that prevent or inhibit the aggregation of crystals. Reduced levels of stone inhibitor substances contribute to the formation of kidney stones. Urolithiasis is the medical term used to describe urinary stones. It is to be noted that the composition of gall stones (found in the gall bladder) and kidney stones is different.

What are the size, shape and location of urinary stones?

Kidney stones vary in size and shape. They can be smaller than a grain of sand or can be as large as a tennis ball. The shape of the stone may be round or oval with a smooth surface, or they can be irregular or jagged with a rough surface. Stones with a smooth surface cause less pain and their chances of natural removal are high. On the other hand, kidney stones that have an irregular rough surface can cause more pain and are less likely to come out on their own. Stones can occur anywhere in the urinary system but occur more frequently in the kidney and then descend into the ureter, sometimes lodging in the narrow areas of the ureter.

Stones in the urinary tract are an important cause of unbearable abdominal pain.

What are the types of kidney stones?

There are four main types of kidney stones:

1. Calcium Stones: This is the most common type of kidney stone, which occurs in about 70 - 80% of cases. Calcium stones are usually composed of calcium oxalate and less commonly, of calcium phosphate. Calcium oxalate stones are relatively hard and difficult to dissolve with medical management. Calcium phosphate stones are found in alkaline urine.

2. Struvite Stones: Struvite (Magnesium ammonium phosphate) stones are less common (about 10 - 15%) and result from infections in the kidney. A struvite stone is more common in women and grows only in alkaline urine.

3. Uric Acid Stones: Uric acid stones are not very common (about 5 - 10%) and are more likely to form when there is too much uric acid in the urine and urine is persistently acidic. Uric acid stones can form in people with gout, who eat a high animal protein diet, are dehydrated or have undergone chemotherapy. Uric acid stones are radiolucent, so are not detected by an X-ray of the abdomen.

4. Cystine Stones: Cystine stones are rare and occur in an inherited condition called cystinuria. Cystinuria is characterized by high levels of cystine in the urine.

Urinary stone occurs most frequently in the kidney and ureter.

What is a staghorn stone?

A staghorn calculus is a very large stone, usually struvite, occupying a large part of the kidney and resembling the horns of a stag (deer), thus it is called staghorn. A staghorn stone causes minimal or even no pain, diagnosis is missed in most of the cases and end result is damage to kidney.

Which factors contribute to the formation of urinary stone?

Everyone is susceptible to stone formation. Several factors that increase the risk of developing kidney stones are:

  • Reduced fluid - especially decreased water intake and dehydration.
  • Family history of kidney stones.
  • Diet: consuming a diet high in animal protein, sodium and oxalate, but low in fiber and potassium rich citrus fruits.
  • 75 % of kidney stones and 95% of bladder stones occur in men. Men between the age of 20 to 70 years and those who are obese are most vulnerable.
  • A person who is bed-ridden or immobile for a long period.
  • A person living in a hot humid atmosphere.
  • Recurrent urinary tract infections and blockage to the flow of urine.
  • Metabolic diseases: hyperparathyroidism, cystinuria, gout etc.
  • Use of certain medications such as diuretics and antacids.
Reduced water intake and family history of kidney stones are two most important risk factors for stone formation.