|
||||||
|
|
|
|
|||||||||||
|
|||||||||||||
| ||||||||||||||||||||||||||||||||||||
Like other medical conditions once found only among adults, nonalcoholic fatty liver disease (NAFLD) has crept into the pediatric population. But clinicians lack standards for when and how to diagnose it.
"This dwarfs diabetes in terms of prevalence," says Jeffrey B. Schwimmer, MD, associate professor of pediatrics in the division of gastroenterology, hepatology, and nutrition at University of California, San Diego's department of pediatrics. "There's no question that this is the most chronic, serious consequence of childhood obesity. It deserves way more attention. The majority of children who have NAFLD are undiagnosed."
That said, it should be noted that NAFLD generally is asymptomatic, and its predominant form poses no immediate health threats. However, a particular form of NAFLD—nonalcoholic steatohepatitis (NASH)—is a serious condition associated with cirrhosis of the liver. Benign NAFLD can progress to NASH.
Schwimmer and associates determined that an estimated 9.6% of U.S. children and adolescents ages 2–19 have NAFLD in the first study of the disease's occurrence in this age group.1 "That is a huge number," Schwimmer says.
The results were published in the October 2006 issue of Pediatrics.1 Findings were gleaned from autopsies and were adjusted for age, gender, race, and ethnicity.
The NAFLD risk for overweight adolescents is of particular concern, according to experts. "Of obese adolescents, between 50 and 75% have NAFLD," says Ariel Feldstein, MD, a pediatric gastroenterologist specializing in pediatric liver disease at the Cleveland Clinic main campus.
DETECTING NAFLD
To date, no formal guidelines have been developed nor do experts agree on the best way to screen for NAFLD and diagnose it. The American Medical Association, however, has convened a task force that will issue guidelines regarding various aspects of child and adolescent overweight and obesity, including NAFLD. Schwimmer is a task force participant.
In the rare instances when NAFLD symptoms appear, they are vague, making them unreliable disease indicators. "Some children, around 20 to 25%, will have either abdominal pain or fatigue," Schwimmer says.
Most experts do agree that a watch-and-wait approach is not acceptable. "We cannot wait for symptoms to appear. We have to be proactive," Feldstein says.
Schwimmer recommends screening all obese children 
8 years with an
alanine aminotransferase (ALT) test, which a primary care provider can order.
Children whose lab work demonstrates even slightly elevated liver enzyme
levels should be considered for further screening, he says. According to
Schwimmer, pediatricians who believe a patient may have chronic liver disease
generally refer that patient to a pediatric hepatologist.
"Children with persistently elevated liver chemistry and positive autoimmune blood markers deserve a biopsy," he says.
Miriam Vos, MD, a pediatric hepatologist at Emory University School of Medicine in Atlanta, offers more conservative advice. "I tell pediatricians, NAFLD usually presents at around age 12. Patients who have been overweight for a while and are 12 or over should be screened."
Vos also points to other risk factors that, when combined with obesity, increase the likelihood of NAFLD and further convince her of the need for screening. These characteristics include:
HOW TO SCREEN
Most pediatric liver specialists agree that a liver biopsy should not be the first step of the diagnostic process, but there is disagreement over where to start.
Vos begins with blood work. "Screening that involves ALT and AST [aspartate aminotransferase] blood work is not perfect, but it's pretty good," she says. If the enzymes remain elevated after a second blood test, Vos generally recommends a workup for a host of liver diseases. If the comprehensive workup fails to identify the source of the problem, and the blood work indicates other warning signs, then she recommends a liver biopsy.
Feldstein disagrees with using blood work as part of the diagnostic process. "Testing for liver enzymes is of very limited utility. It's no better than 40% accurate. Some say you would miss two-thirds of cases if you were checking just elevated enzymes," he says.
He prefers to start the screening process with an ultrasound. "I strongly encourage pediatricians to use the liver ultrasound. It's very sensitive in detecting lipids in the liver," Feldstein says. And although the test is expensive, most insurance companies cover its cost, he adds.
|
But the ultrasound has drawbacks, some clinicians note. It typically will not detect the presence of fat in the liver until it reaches about 30%, but the liver is considered fatty once the fat content is >5%, Schwimmer says. And ultrasound results depend on the expertise of the technologist performing the test and the radiologist interpreting the results, he says, whereas a blood test renders the same result regardless of other factors.
The ultrasound also has limited diagnostic capacity. "You cannot tell which kind of NAFLD a patient has—NASH or the benign form," Feldstein says.
LIVER BIOPSY: THE CONCLUSIVE TEST
Regardless of how a physician initiates the diagnostic process, currently the biopsy is the only method of providing a conclusive diagnosis of NAFLD. Experts offer conflicting advice on when to biopsy or who should order it but agree that, when repeated screenings come back suspect, it is time to biopsy.
A biopsy proves useful for two reasons, Schwimmer explains. For starters, it is the only available method that provides a definitive diagnosis. Second, a biopsy enables a clinician to assess the severity of the disease. "NAFLD is a spectrum disorder, ranging from the accumulation of fat in liver cells alone, to fatty hepatitis, to fatty hepatitis with scar tissue," Schwimmer says. Of the patients he biopsies, 5–10% already exhibit advanced liver disease.
But the recommendation to perform liver biopsies on children often meets with opposition because the procedure is perceived as quite invasive, Feldstein says. "There's a lot of resistance from patients and parents, although it is safe."
However, new tests may be on the horizon. "Many research groups are working on finding new biomarkers that can replace the liver biopsy, which is now the only way to really distinguish NASH from NAFLD and the only way to tell how much scarring is present," Feldstein says.
To manage NAFLD once a child has it, hepatologists typically recommend physical activity and, at times, weight loss. A combination of weight loss or maintenance and increased exercise often improves a child's liver numbers, says Vos.
"We have a nutritionist who works in our clinic and sees every family," says Vos. "I find that very helpful."
Currently, such lifestyle intervention is the most effective tool clinicians possess in the absence of good tests to diagnose NAFLD versus NASH, or the progression from NAFLD to NASH, says former American Diabetes Association president Francine R. Kaufman, MD, now a pediatrics professor at University of Southern California's Keck School of Medicine. She believes schools should be more involved in educating children about liver disease.
"We need better markers, but in the interim all kids who are
overweight or obese should get lifestyle education because they may get fatty
liver disease," says Kaufman. "The way to get this done is with
advocacy to place it as part of the school curriculum." 
Footnotes
Mayo Clinic researchers in Rochester, Minn., identified nonalcoholic fatty liver disease (NAFLD) in 1980. Each year, hepatologists at Mayo Clinic evaluate and treat >2,500 adults and children with NAFLD. More information is available at www.mayoclinic.org/nonalcoholic-fatty-liver-disease.
The Fatty Liver Clinic at Children's Hospital and Health Center in San Diego, affiliated with the University of California, San Diego, and established in 2002 by Jeffrey Schwimmer, MD, and Joel Lavine, MD, was the first clinic in the U.S. dedicated to the care of children and adolescents with fatty liver disorders. Find out more at www.pediatrics.ucsd.edu/C16/Fatty%20Liver%20Clinic/default.aspx.
References
CiteULike 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
| ||||||||||||||||||||||||||||||||||||
|
||||||
|
| DOC News | Diabetes | Diabetes Care | Clinical Diabetes | Diabetes Spectrum |
