Urinary Tract Stones

Overview:

Treatment of urinary tract stones dates back to antiquity and has relied mostly on open surgery. The treatment did not come into the “space age” until the early 1980’s with the introduction of extracorporeal shock-wave lithotripsy (ESWL), and the miniaturization of instruments to allow access to the ureter. This has almost eliminated open stone surgery today.

Predicting Factors:

Genetics

25% of patients with kidney stones have a family history of stones. In a longitudinal study of 37,999 male health professionals, a family history of stones was more than three times higher in men with kidney stones than in non-formers. The lack of evidence associating environmental factors with kidney stones also favors the influence of genetic components to kidney stone formation.

Age and Sex

The peak incidence is from the twenties to the forties. The proportion of male to female incidence is 3:1. Increased urinary citrate concentrations was found in the urine of women, and is thought to provide a protective effect from calcium stones. Patients with recurrent stones tend to have lower levels of urinary citrate.

Extrinsic Factors

Geography

The prevalence of urinary calculi is higher in those who live in mountainous, desert, or tropical areas. Geography, however, represents just one factor among a multitude of others – such as dietary habits, temperature, and humidity – superimposed on the
intrinsic factors that predispose to stone formation.

Climactic and Seasonal Factors

The incidence of urinary calculi is higher during the summer months. High temperatures increase perspiration, which may result in concentrated urine and this promotes crystallization. An alternative viewpoint is that increased exposure to sunlight causes
increased production of vitamin D leading to increased calcium excretion in the urine.

Water Intake

It is an accepted truism that increase water intake and increased urinary output decreases the incidence of urinary calculi in those predisposed to form stones. This has been verified by the incidence of stone formation and its relationship to fluid intake.

Diet

Dietary intake of various foods may result in greater urinary excretion of substances that have an effect on the incidence of urinary calculi. However, the underlying intrinsic tendency to form stones also has to be present. Increased oxalate, calcium or sodium in the urine of patients predisposed to stone formation, can lead to an increased incidence of stones. Increase ingestion of animal proteins can also lead to increased urinary concentrations of calcium, oxalate and uric acid.

Physical Activity

Urinary calculi are much more likely to be found in individuals who are sedentary. The risk of calcium oxalate and uric acid stone formation increases after a space flight, because of the microgravity environment of space.

Stress

Studies show that stress can also be a factor significantly associated with stone disease.

Metabolic Factors

Urinary stones occur due to the formation of crystals and crystal aggregates in the urine. Normal individuals have inhibitors of crystal formation and growth in the urine in the form of compounds like citrate, magnesium and certain proteins. There is a
fine balance between the various physical and chemical factors that keep crystals in solution. This balance can be affected at multiple points to lead to crystal formation and aggregation, which leads to stone development. Bacterial infections may promote stone formation by increasing crystal adherence.

Clinical Presentation

Acute Stone Episode

Pain is the most common presenting symptom and it tends to occur during the night or early morning hours. Pain tends to be colicky, appears in the flank and radiates to the area of the groin. Urinary frequency or urgency is noted, as the stone gets closer to the
bladder. Localized ureteral irritation can affect the gastrointestinal tract and produce associated bloatiness, nausea, vomiting or diarrhea. Fever, if present, can indicate associated infection, which makes the presentation a medical emergency. The urine in most patients reveals the presence of microscopic or gross hematuria.

Medical Therapy

Treatment of existing stones is either medical if small enough to pass, or procedural if too large. This will be carried out under the supervision of an urologist. The secondary purpose of medical therapy is to prevent new stone formation. So, who needs medical
therapy?

  • Patients in whom the initial episode involves multiple stones.
  • Patients who have had a stone recurrence within 1 year of follow-up.
  • Patients who have risk factors for recurrence.

General Measures of Prevention

Hydration

Historical data strongly suggest that hydration is effective in preventing stone formation. An increase in urine volume of only one cup per day was associated with a protective effect. Ideally, the fluid intake should be enough to maintain a urine output of 2.5-3 quarts a day. Interestingly, a large study of 81,000 women, showed a decrease incidence of stone formation in women drinking 8 oz. of wine daily, but showed an increase incidence if drinking similar amounts of grapefruit juice. Also another study found the consumption of one bottle of beer a day reduced the risk of stone formation by 40%.

For more information on how sugary drinks may increase kidney stones, please go here.

Diet

Epidemiologic studies have shown that the incidence of renal stones is higher in populations in which protein intake is greater. Proteins increase urinary calcium, oxalate, and uric acid excretion and the mathematically calculated probability of stone formation even in normal subjects. In two large studies, the prevalence of stone disease and the incidence of new stone formation were directly associated with weight and body mass index. This association was greater in women. This observation suggests that
weight reduction may be one method of preventing stone disease.

Dietary Calcium

Contrary to popular belief, a higher intake of dietary calcium was strongly associated with a decreased risk of kidney stones. The intake of supplemental calcium was positively associated with risk. This may be due to the timing of the calcium ingestion or to factors other than the calcium in diary products. This suggests that dietary calcium restriction is inappropriate for patients with calcium stones, and may even be detrimental.

Dietary Sodium

Increased dietary sodium leads to increased calcium in the urine. Patients with recurrent stones do not ingest more sodium, but they are more sensitive to it. Avoiding excessive sodium is a good strategy in avoiding recurrent calcium stone formation.

Dietary Oxalate

Only about 10% of urinary oxalate comes from dietary sources. The rest comes from liver metabolism and the conversion of ascorbic acid (40%). Thus it appears prudent to avoid an excess of vitamin C in patients with recurrent calcium oxalate stone formation.

Dietary Fiber

Patients with calcium oxalate stones eat less dietary fiber than healthy subjects. Fiber binds intestinal calcium and decreases calcium absorption. Fiber also decreases intestinal transit time.

Summary

  • High fluid intake
  • Limit meat intake
  • Substitute whole wheat bread for white bread
  • Eat natural fiber cereals
  • Sodium restriction
  • Limit oxalate-rich foods and vitamin C
  • DO NOT restrict dairy products, but avoid overindulgence
  • Increase intake of citrate (lemonade) or citrus fruits

Special Situations

Prostatic Calculi

Prostatic stones occur frequently in men older than 50 years. They are asymptomatic and found incidentally during work-up for other conditions. This is an aging process and typically has no clinical significance. The stones are usually calcium phosphate. Symptoms, when present, may be due prostatic enlargement (BPH), chronic prostatitis, or terminal urinary bleeding or spotting. In some cases bloody ejaculate or perineal discomfort is noted.

Stones in Pregnant Women

Although pregnancy does not predispose to calculi, physiologic dilatation of the ureters and renal pelvis allow preformed calculi to move or migrate resulting in renal colic and hematuria. Ultrasound has become the cornerstone of evaluation in pregnancy. The first trimester is the most significant risk period for radiation exposure. If indicated, resolution of obstruction with stents under ultrasound monitoring is the way to go. Pregnancy is an absolute contraindication for lithotripsy in any form and should be delayed until after the delivery.