A new epidemic: kidney stones in children?

This is a pop quiz of critical thinking skills:

1. If you are a major medical center and begin to offer special diagnostic imaging equipment and treatment devices (like extracorporeal shock wave lithotripsy) sized for children with a rare condition, then you advertise your specialized services, and see more children with this condition coming to your center for care, does this mean:

a). more children are coming to your regional center because you provide a valuable service unavailable elsewhere

or

b). there is a nationwide increase in the numbers of children with this condition?

2. If select treatments are used for the clinical management of people with certain genetic or metabolic conditions, does this mean:

a). this treatment may be appropriate for the specific management of these conditions

or

b). if everyone followed this treatment regimen, it could prevent healthy people from ever getting this condition?

3. If a writer pieces together press releases and testimonials, is it possible to create a new epidemic and get professional and consumer publications to believe it?

a). No, of course not, healthcare professionals and professional journalists and editors fact check, go to original and objective sources, and would never fall for that.

or

b). Yes, of course. ;-)

Question #1 was an example of the Land of Incognita fallacy of logic. Question #2 was an illustration of turning a treatment into a preventative, sort of like saying we should all be on chemotherapy to prevent cancer or a diabetic diet to prevent diabetes. Question #3 was a reminder that press releases and anecdotes are not scientific evidence and we are ill-advised to rely on media to go to original research and accurately reported its findings. If these three questions seem far fetched or an exaggeration, you weren’t paying attention to this past week’s news…

The news version

On Tuesday, an article reporting that there has been a sharp rise in kidney stones among children in the United States, was simultaneously published in the New York Times and the International Herald Tribune. Kidney stones were blamed on an epidemic of childhood obesity and children today eating bad diets that are purportedly too high in salt, fat, sugar and processed foods. The news story added that kidney stones have also been increasing among adults in their 20s and 30s, as a spillover of the obesity epidemic, and are no longer just more common in middle-aged adults.

Within one day, 2,343 stories had been published around the world reporting steep increases in the number of American kids getting kidney stones (per Google news search); and the story has already been embellished, with claims that research has shown diet to be the leading cause.

Laurie Tarkan, a health reporter who contributes to the New York Times and women’s magazines, cited information and quotes from four pediatric medical centers, all with special kidney stone units: Children’s Hospital of Harvard medical School in Boston, Massachusetts; Vanderbilt Children’s Hospital in Nashville, Tennessee; University of Wisconsin Health in Madison, Wisconsin; and Johns Hopkins Children’s Center in Baltimore, Maryland. No independent sources of information were included in this article.

Each of these kidney stone centers had also issued press releases and posted nearly identical information on their websites between 2002 and 2006 [noted in links]. As reported:

A Rise in Kidney Stones Is Seen in U.S. Children

To the great surprise of parents, kidney stones, once considered a disorder of middle age, are now showing up in children as young as 5 or 6. While there are no reliable data on the number of cases, pediatric urologists and nephrologists across the country say they are seeing a steep rise in young patients. Some hospitals have opened pediatric kidney stone clinics.

“The older doctors would say in the ’70s and ’80s, they’d see a kid with a stone once every few months,” said Dr. Caleb P. Nelson, a urology instructor at Harvard Medical School who is co-director of the new kidney stone center at Children’s Hospital Boston. “Now we see kids once a week or less.”

Dr. John C. Pope IV, an associate professor of urologic surgery and pediatrics at the Monroe Carell Jr. Children’s Hospital at Vanderbilt in Nashville, said, “When we tell parents, most say they’ve never heard of a kid with a kidney stone and think something is terribly wrong with their child.”…

The increase in the United States is attributed to a host of factors, including a food additive that is both legal and ubiquitous: salt… “What we’ve really seen is an increase in the salt load in children’s diet,” said Dr. Bruce L. Slaughenhoupt, co-director of pediatric urology and of the pediatric kidney stone clinic at the University of Wisconsin. He and other [unnamed] experts mentioned not just salty chips and French fries, but also processed foods like sandwich meats; canned soups; packaged meals; and even sports drinks like Gatorade, which are so popular among schoolchildren they are now sold in child-friendly juice boxes.

Children also tend not to drink enough water. “They don’t want to go to the bathroom at school; they don’t have time, so they drink less,” said Dr. Alicia Neu, medical director of pediatric nephrology and the pediatric stone clinic at Johns Hopkins Children’s Center in Baltimore. Instead, they are likely to drink only once they’re thirsty — but that may be too little, too late, especially for children who play sports or are just active…

This news story is very similar to one published on September 18^th by HealthDay*, entitled: “More kids getting kidney stones — Doctors blame sedentary lifestyle, obesity, poor diet.” It reported the same sources as saying they are seeing growing numbers of children with kidney stones. Despite the lack of hard numbers of children with kidney stones, the article said that experts feel certain there are more kids with kidney stones.

Reading closely, the only evidence for the incidences, causes and preventative measures presented in these articles were anecdotal. But beliefs and opinions, rather than sound scientific evidence, have this troubling tendency of also giving contradictory and confusing information. According to the articles, parents can help prevent kidney stones in their children by promoting a healthy diet and lifestyle; reducing salt, added sugars and processed foods; drinking lots of non-caffeinated liquids and water, and getting exercise. But readers also read that “there’s not much that parents can specifically do to prevent kidney stones in their children.” And in contrast to the increase in kidney stones seen at Children’s Hospital attributed to increased incidences of obesity, we also read that most of the kids being seen appear to be reasonably fit and active and they’re “not seeing a parade of overweight Nintendo players.”

Sadly, these news stories mostly foster the belief that good health is the reward of good diets and lifestyles, and give the cruel message that patients, even our youngest, are partly to blame for their health problems because of unhealthy diets and lifestyles.

The medical literature on pediatric nephrolithiasis (kidney stones)

There are no solid national statistics or trend data for the United States or Canada, but available figures consistently show that kidney stones are uncommon in children.

In a study by pediatric nephrologists published in the August 2008 issue of the journal of the Canadian Urological Association, Dr. Laura Chang Kit and colleagues at the University of Ottawa’s Children Hospital of Eastern Ontario, explained that kidney stones account for only about 1 in 1,000 to 1 in 7,600 pediatric hospital admissions across North America. Overall prevalence has been estimated at about 1-5%, as not all cases require hospitalization. While stones are less frequent in children and teens than in adults, doctors are increasingly recognizing that they do occur in young people and, as the Canadian researchers noted, the medical literature is increasingly urging primary care physicians to look for kidney stones in young persons with suggestive symptoms. This enhanced identification could also contribute to perceptions of rising numbers.

Pediatric kidney stones are not yet fully understood and most of what is known comes from reports of the experiences of individual medical centers. With urolithiasis among pediatric patients uncommon, a complete grasp of the types of stones young people develop, the causes, symptoms presenting at various ages and stone compositions, and the appropriate management remains controversial, according to doctors from Mayo Clinic. In a retrospective analysis of 221 pediatric kidney stone patients seen at the Mayo Clinic from 1965 to 1987, they reported that nearly one-third of the children with kidney stones had had structural abnormalities of the genitourinary tracts; nearly one in five had infection-related stones; and just over half of the children (52%) had conditions that led to metabolic abnormalities in their urine, such as hypercalciuria (33.8%) and hyperoxaluria (20.2%). Like adults, kidney stones often reoccur, and 67% of their pediatric patients had two or more stones during the 5 years they were followed.

A 2002 Vanderbilt University Medical Center study, published in the Journal of Urology just before it opened its regional pediatric kidney stone clinic, noted that children who get kidney stones usually develop them from one of two sources: metabolic abnormalities or infections. Historically, they said, pediatric stones have been associated with urinary tract infections in as many as 78% of cases, while more recently, infections are found in 14% to 20%. Doctors at Alder Hey Children’s Hospital in Liverpool, for instance, followed the 270 consecutive patients seen at their hospital over a 27-year period and found that 60% of them had infection-related stones.

In a retrospective review of their medical records, there were 152 consecutive cases of children with kidney stones seen at Vanderbilt from April 1992 through 1999. One in seven cases were children born with anatomical abnormalities (such as primary ureteropelvic junction obstruction with secondary stones). Excluding the structural defects from their analysis (along with two more due to incomplete medical records), they reported that half of the remaining children under age ten had metabolic abnormalities believed to be responsible for their stones. And among all ages of children, 90% of recurrent stones occurred in those with metabolic disorders.

The predominance of kidney stones among younger children were related to medications, they reported, most notably having been preemies, with higher numbers of them on lasix medication for pulmonary diseases. Younger children were also more likely to have stones caused by systemic illnesses or diseases and larger stones that the youngsters were unable to pass spontaneously. In contrast, they reported, children over ten years of age had more stones related to kidney causes, such as hypercalciuria and hypocitruria.

A metabolic cause for kidney stones in children has been found in 30-95% of cases, depending on the population being seen at various medical centers.

Metabolic disorders produce stones with different chemical compositions, shapes and sizes; and they’re each treated differently.

The most common types of kidney stones, according to the pediatric nephrologists at Vanderbilt and the University of Washington in Seattle, are calcium stones (caused by excessive calcium in the urine from increased absorption of calcium, 45-65% calcium oxalate, 14-30% calcium phosphate), followed by struvite stones (associated with bacterial infections, found in 13% of pediatric kidney stone cases), cystine stones (often genetic and forms from cystine buildup in the urine, 5% of cases), and uric acid stones (caused by too much uric acid in the urine, 4% of cases). These metabolic disorders can be inherited. There are a variety of conditions with higher risks for stone formation in children, including juvenile rheumatoid arthritis, other genetic conditions such as Bartter’s syndrome and Dent’s disease, inflammatory bowel disease, hyperparathyroidism, osteoporosis, corticosteroids or furosemide medications, and gastrointestinal disorders.

The most recently published medical center study of children diagnosed with kidney stones was at the Children’s Hospital of Eastern Ontario, which reviewed the 72 cases seen there from January 1999 through July 2004. Dr. Kit and colleagues found that 25% of the children had a family history of stones, 2 out of 5 children had metabolic disorders, and one in seven had genitourinary anatomical defects (most frequent was ureteropelvic junction obstruction). “Five patients (7%) had bilateral disease, with 4 of 5 having associated metabolic abnormalities (2 hypercalciuria, 1 hypocitraturia, 1 Jacobsen syndrome). Jacobsen syndrome is a partial 11q deletion syndrome associated with mental and growth retardation, craniofacial, cardiac, orthopedic and genitourinary abnormalities, including cryptorchidism, collecting system duplications, horseshoe kidney and pyelectasis. Like other patients with Jacobsen syndrome, our toddler had metabolic abnormalities related to dehydration and failure to thrive, as well as bilateral hypodysplastic kidneys.”

Take home message: The point here is that kidney stones remain fairly uncommon in American children, with even major regional medical centers seeing only handfuls of cases a year, and it’s a condition that is a symptom of specific medical problems, not something most healthy children get simply by eating certain foods.

There is no credible evidence to support fears of soaring increases of kidney stones among American children and teens. Diet alone also doesn’t cause kidney stones; the evidence does not exist. Nor do parents need fear that their children’s diets and health are as horrible as media continually reports. There is also no sound evidence to support the need or health benefits of salt-reduced diets for children or adults in the general population. In fact, the available evidence fails to even support a link between the amounts of salt eaten by American children and claims of rising rates of kidney stones. While the Vanderbilt doctors reported that about two-thirds of 6-10 year old children with kidney stones were boys, for instance, NHANES dietary intake data, which is based on a representative sampling of the U.S. population, reveals that sodium intake among boys that age has remained stable, even showing a slight decrease (from 3,272 mg/day in 2001-2002 to 3,202 mg/day in 2005-2006).

And among the entire population from age two, overall sodium intakes have remained remarkably consistent for the past two decades.

Kidney stones are not a disease, not new, and not all the same

Misperceptions that kidney stones are a manifestation of today’s modern foods or lifestyles, and other misunderstandings of kidney stones, were addressed in an overview of the pathophysiology and medical management of kidney stones by Dr. Orson W. Moe, M.D., director of the Charles and Jane Pak Center of Mineral Metabolism and Clinical Research and with the Department of Internal Medicine at the University of Texas Southwestern Medical Center in Dallas, Texas.

Writing in a 2006 issue of Lancet, he explained: “Urinary tract stones (urolithiasis) can be traced to the earliest antiquity of human history.” One added precaution in interpreting contemporary figures on the prevalence of kidney stones is to remember that with the widespread use of diagnostic imaging, nephrolithiasis can also even present as an incidental finding on a radiograph, sonogram, or CT scan.

Our understanding of kidney stones is slowly evolving, as are the genetic defects that lead to them. But, most important to remember, is that “nephrolithiasis is not a true diagnosis because kidney stone formation can suggest a broad list of underlying diseases,” he wrote. “Nephrolithiasis per se is not much more of a diagnosis than, for example, arthritis, edema, ascites, or fever.” Kidney stones are a symptom.

Kidney stones can be a secondary complication of all sorts of metabolic and anatomical problems and even urinary tract infections, as we’ve seen. Doctors at Mayo Clinic recently reported that nearly one-third of bariatric patients develop kidney stones two years out from their surgeries, as a symptom of malabsorption and malnutrition. And a number of commonly-prescribed medications can increase the formation of kidney stones, such as topiramate for seizures and migraines, as researchers at U.T. Southwestern Medical Center have found.

The medical management of the stones depends on their specific pathophysiology. “The formation of stones in the urinary tract stems from a wide range of underlying disorders,” Dr. Moe emphasized, and it’s imperative that doctors look for the underlying causes in order to determine the appropriate medical management of each individual patient.

[When reading studies on prevention and the medical management of people with kidney stones, it’s important to differentiate secondary prevention — efforts to prevent recurrence of kidney stones among stone formers, interventions that are individualized based on the particular composition of their stones, and the possible structural, metabolic or infectious contributing causes — from claims of preventing stones among healthy children without such underlying stone-forming conditions. The only randomized clinical trial of increasing water intake as a preventive measure for kidney stones, for instance, was done in Italy on 199 patients with single calcium oxalate stones looking at recurrences, said Dr. Bernhard Hess, M.D., at the Departments of Internal Medicine and Nephrology at Hospital Zimmerberg in Switzerland, writing in the special 2002 kidney stone issue of Endocrinology and Metabolism Clinics of North America.]

Diluting the urine with increased fluid intake has generally been shown to be helpful in epidemiological and prospective studies for managing people with a history of kidney stones. “The type of drink seems to matter, since orange juice, coffee and alcohol are especially beneficial, but the most important component is probably water,” Dr. Moe wrote.

But the diet-related management of kidney stones is dependent on the urinary chemistry and type of stones. All stones are not the same, just as all underlying causes are not the same. As the science evolves, special “caution is indicated when one generalizes from studies done in healthy volunteers and the general population to stone formers,” Dr. Moe wrote. This is particularly evident when it comes to calcium.

“The recommendation for the optimum dietary calcium intake has changed from the traditional wisdom of calcium restriction to high dietary calcium being protective, to a position in between, although some clarification is needed. The continuing theory is that because calcium binds oxalate in the bowel, any gain from reduction of urinary calcium from dietary calcium restriction might be negated by a rise in urinary oxalate,” which he went on to explain in depth.

In patients with absorptive hypercalciuria with enhanced intestinal calcium absorption, the rise in urinary calcium from high calcium intake is so large as to overwhelm any reduction in urinary oxalate. Conversely, dietary calcium restriction might produce a substantial reduction in urinary calcium in hypercalciuric patients, but a negligible change in normocalciuric patients. A diet high in calcium is sometimes rich in potentially protective factors, such as potassium, magnesium, and fluids. Thus, in stone formers with normocalciuria, a severe dietary restriction is not indicated because of the exaggeration of secondary hyperoxaluria and potential risk for bone loss. In those patients with hypercalciuria, calcium intake might be restricted especially when it is applied with a hypocalciuric agent. In both groups, dietary oxalate intake should be restricted.

To put all of this more simply, calcium can increase the formation of kidney stones in patients with certain types of stones: calcium oxalate or calcium phosphate stones. Popular advice to increase dietary intake of calcium to prevent kidney stones, “could be a dangerous recommendation for some individuals,” said Dr. Margaret Pearle, professor of urology and internal medicine at UT Southwestern, who has co-authored research on calcium and the formation of kidney stones.

Dr. Charles Y.C. Pak, lead author on studies of calcium oxalate and phosphate stones, and former director of the Charles and Jane Pak Center for Mineral Metabolism and Clinical Research at UT Southwestern, urged patients to talk to their doctors before either limiting or increasing the calcium in their diets. The take-home message of the research, he said, “is that the recommendation for calcium intake cannot be generalized since the effect of calcium intake on stone formation depends on the type of stone, oxalate intake, presence of stones and the efficiency of calcium absorption from the bowel.”

“While we want to be cautious in asking anyone to restrict calcium intake because of the risk of bone disease, we also realize that urinary calcium has about the same influence as urinary oxalate in calcium oxalate stone formation,” said Dr. Pearle. For patients with elevated intestinal absorption of calcium and urinary calcium levels, they may be advised to reduce calcium in their diet. And patients with calcium phosphate stones may also need to carefully monitor their calcium dietary intake, said Dr. Beverley Adams-Huet, at UT Southwestern's General Clinical Research Center.

There are very real risks for consumers who rely on popular media for medical advice. The New York Times article, for example, said that it was a myth that people with kidney stones should avoid calcium. Instead, it incorrectly stated: “In fact, dairy products have been shown to reduce the risk of stones, because the dietary calcium binds with oxalate before it is absorbed by the body, preventing it from getting into the kidneys.”

Is there even evidence for steep increases of kidney stones among U.S. adults?

The only study said to examine trends in kidney stones in the United States had been led by Dr. Kiriaki K. Stamatelou of the Renal Unit at Blue Cross Hospital in Athens, Greece; and conducted with colleagues from Joslin Diabetes Center in Boston, Massachusetts; National Institute of Diabetes and Digestive and Kidney Diseases at the National Institutes of Health in Bethesda, Maryland; and Brigham and Women’s Hospital in Boston. It estimated the prevalence of kidney stones using NHANES data on adults ages 20-74 from 1976 to 1994 and was published in 2003 in the journal Kidney International.

Reading the study, however, reveals that it dispelled support that kidney stones were actually increasing among U.S. residents — even though this is the study popularly cited to support claims of an increase!

Since this is the strongest and only study to date to look at the long-range population-wide trends of kidney stones in the U.S., it deserves a closer look. According to the abstract, the prevalence of kidney stones among 20- to 74-year-olds increased from 3.8% in 1976-1980 to 5.2% in 1988-1994; prevalence was greater among men than women, and increased with age at every range of years examined; age-adjusted prevalence was highest in the South and lowest in the West; and Caucasians had nearly double the rates of either Hispanics or blacks.

But this doesn’t give the full story. A closer read of the text and actual data reveals that the differences in prevalence of kidney stones between 1976 to 1994 were not statistically significant for any age group except for 70-74 year olds and 40-49 year old females.

In contrast to the New York Times story, there’s been no statistical increase in kidney stones among young adults in their 20s or 30s since 1976.

The authors added that “stratified analysis by age group found a statistically significant increased prevalence only in 60-74 year old Caucasians, but not in African Americans of comparable ages.” Only by combining all of the ages and genders did the increases reach statistical significance.

But… They noted that “several factors may have contributed to these observed elevations in prevalence.” The most notable, of course, was “better detection and/or diagnosis of kidney stones.” As they pointed out: “It is also possible that more frequent renal ultra-sound studies due to different care patterns and technical advances might have caused a slight increase of kidney stone detection in NHANES III.”

The authors of this study added another cautionary note in interpreting a purported increase in prevalence of kidney stones. They used self-reported kidney stone histories, without confirmation from medical records, and “recall bias might have influenced the quality of information provided by study subjects.”

The temporal trend may also reflect different survival rates, they said, because of “disproportionately higher mortality prior to 1976 compared to subsequent years among individuals affected with stone disease.” The greatest risk factor for kidney stones was age, with men ages 60-75 having more than a 5-fold risk compared to those age 20-39, and older women more than double the risks of young women.

This study did analyze the effects of dietary intakes of calcium, total fat, protein, and consumption of tea, coffee, and plain drinking water on risks for stone disease among the population. They were unable to find an association with any of these variables, even factoring for diuretic use, age, sex, race/ethnicity and other confounding factors.

In contrast to the New York Times story, kidney stones trends since 1976 were unrelated to not drinking enough water, drinking too much caffeinated drinks, or eating too much fat or protein.

The authors also downplayed the regional differences reported in their paper, and were unable to explain them. A closer look finds higher life-time prevalence was seen among people living in the South, but only when compared to the West and Midwest, but not the Northeast. But “none of the personal risk factors that we studied appeared to account for the observed regional variation in lifetime prevalence of kidney stones.” Dietary factors, such as protein intake, were unrelated to the regional variations in kidney stones, they reported. They also cautioned that they were unable to examine causal roles “for these hypothesized associations due to lack of data [and] our data were cross-sectional.” The most likely explanation for the geographic variation in risk for kidney stones, calcium content in community water systems, was found to not be associated with the prevalence of renal stones in a previous study of women in the Midwest, so the geographic association remains unclear, they said.

This is as good as the evidence gets to suggest rising kidney stones among the American population — based on data more than a decade old that even the authors admitted could be explained by heightened diagnostics and survival rates, of a condition in which most patients have reoccurring stones, and a study that the authors were unable to find evidence to support any possible biological explanation for a true increase.

Going back to our Pop Quiz and the news, there is even less evidence to suggest steep increases of kidney stones among America’s children. Nor is there evidence that parents need to be scared that their children are in danger of getting yet another worrisome condition if they don’t slim them down and change their diets — to water, low-fat, low-salt, low-sugar, low… Sadly, good news about the state of our children's health doesn't make news headlines, but some of that balance might be the most healthful and helpful news of all. What health epidemic will we read about next, as efforts intensify to scare children thin?

© 2008 Sandy Szwarc

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