Follow-up data were available on 21 patients. The mean duration of follow-up was 18 months (range, 2–65 months). Six patients lost weight, and all had improvement in serum aminotransferase levels. In two of these patients AST and ALT completely normalized. Most patients had great difficulty losing weight. The AST and ALT levels fluctuated in those patients who were not able to achieve weight loss. One patient subsequently had severe hypothyroidism.
At the time this study began, whether chronic liver disease resembling alcoholic liver disease but occurring in nonalcoholics actually existed was controversial. Identifying this disease in children provided evidence that NASH as such actually existed. Finding a large number of such patients now suggests that it constitutes a significant problem in pediatric hepatology. The diagnosis of NASH rests in part on histologic findings, and we have accepted steatosis with evidence of necroinflammatory activity as the essential histologic criteria for this diagnosis. In many patients, fibrosis is also present. We believe that the term “nonalcoholic steatohepatitis” is unduly restrictive and prefer the term “nonalcoholic fatty liver disease.” However, the former terminology appears entrenched.
Despite many case series describing NASH in adults, there have been only a few reports of this disorder in children. Moran et al. (9) described three children with obesity and steatohepatitis. In a study of 299 obese children, Kinugasa et al. (10) found 36 (13%) to have abnormal aminotransferases. Liver biopsy was performed in 11 of these children, and results confirmed steatohepatitis. One patient had cirrhosis, along with maturity-onset diabetes mellitus and hyperlipidemia. Vajro et al. (11) reported a series of seven obese children with persistently elevated aminotransferases. These children may have had NASH; however, liver biopsy was obtained in only one patient, and the results showed steatohepatitis. Recently Baldridge et al. (12) reported a series of 14 children with idiopathic hepatic steatosis, identified by retrospective review of results of all liver biopsies performed in a tertiary-care pediatric hospital. All were obese, and most had abnormal AST and ALT. Two patients with test results showing normal liver function were discovered incidentally at laparotomy. In a screening study of 310 obese Japanese children Tazawa et al. (13) found that 24% had elevated serum ALT and 83% had a fatty fibrotic pattern observed on hepatic sonography. This same sonographic appearance was found in 19% of children studied who had normal ALT. Although elevated ALT and fatty liver by ultrasound testing appeared to be somewhat more common in older children with more severe obesity, no statistically significant differences were found in different age groups or with longer duration of obesity. An Italian screening study of 195 obese children found fatty liver by sonography in 55%, elevated serum AST or ALT in 20%, and both features in 15%(14).
In our prospective series of 36 children with NASH, findings were heterogeneous. Obesity was the most common clinical denominator. The average patient had a body weight approximately 50% higher than the ideal for height. Although the mean weight overall was 71 kg, of particular concern was the very obese younger child, specifically, 13 children less than 11 years of age whose average weight was 56 kg. However, six patients were not obese (childhood obesity defined as weight >120% of ideal weight for height). Typically, these children were tall with large bones and proportionately heavy body weight. Unlike some adult series, boys were more common than girls in this series of children. Male predominance was also noted in a Japanese survey of fatty liver detected by sonography in a cohort of 810 children between the ages of 4 and 12 years (16). Approximately half of all patients in the present study had hepatomegaly, and most had elevated serum aminotransferases. Other liver function test results were normal. Eighteen of 20 patients studied had hyperlipidemia; hypertriglyceridemia was more common and more severe.
Long-term follow-up in adults with NASH has shown that the disease is usually slowly progressive but can ultimately lead to cirrhosis in some patients (17,18). Other studies in adults have documented cirrhosis complicating NASH (3–5,8). In this series one patient, a 10 year-old girl with hepatosplenomegaly, had cirrhosis at diagnosis, the second case of cirrhosis in childhood NASH thus far reported. We speculate that some patients with “cryptogenic” cirrhosis occurring in adulthood have in fact had NASH since childhood.
One third of the children in this series had acanthosis nigricans. This association has not been described in other reports of children with NASH. Acanthosis nigricans may be subtle and can be missed without careful examination. Although acanthosis nigricans may occur in simple childhood obesity, it has also been shown to be a cutaneous marker of hyperinsulinemia (19,20). Keratinocytes have receptors for insulin, epidermal growth factor, and insulin-like growth factors. In hyperinsulinemia, circulating insulin, because of its structural similarity to insulin-like growth factor, binds to these receptors and stimulates cell division, leading to acanthosis. Richards et al. (21) reported 22 children with obesity, insulin resistance, acanthosis nigricans, and hyperandrogenemia. Obesity was always the first component of the syndrome to appear. Unfortunately, liver function tests were not obtained in this study.
Other features of the patients in this series suggest that abnormalities of carbohydrate metabolism may be important in the pathogenesis of NASH in children. Two of the patients in our series were known to have diabetes, and two other patients had development of diabetes later. A further patient had insulin-dependent diabetes that developed beyond the period of follow-up for this study at a time when his obesity had resolved and serum aminotransferases were normal. Two patients had Bardet–Biedl syndrome, an inherited syndrome characterized by retinal dystrophy, polydactyly, obesity, renal abnormalities, and male hypogenitalism. Non–insulin-dependent diabetes mellitus (NIDDM) frequently develops, with insulin resistance due to abnormal insulin receptor function (22). Alström syndrome is a rare condition, phenotypically similar to Bardet–Biedl, but distinguished by sensorineural deafness and absence of mental retardation (23). Obesity, hyperlipidemia, NIDDM, and acanthosis nigricans commonly occur in Alström syndrome. Hepatic involvement with mild steatosis, portal inflammation, and moderate fibrosis has been described in one patient (24). Yet another report of a rare syndrome in this Bardet–Biedl/Alström spectrum has been published (25), in which one patient had hepatic steatosis and both patients had decreased insulin receptor binding.
We speculate that abnormal carbohydrate metabolism plays an important role in the pathogenesis of childhood NASH. The high prevalence of acanthosis nigricans suggests that abnormalities in insulin metabolism may be important. Wanless et al. (26) reported hepatic steatosis in a unique subcapsular distribution in patients receiving continuous ambulatory dialysis who took insulin intraperitoneally. In hyperinsulinemia, free fatty acids are preferentially esterified into triglycerides. The resultant hepatic steatosis may incite an inflammatory response, leading to fibrosis. Hypertriglyceridemia was prominent in many of the children in this series. In a few patients tested, hyperinsulinemia was detected. Hyperinsulinemia is characteristic of puberty (27), but recent studies with standardized measurement of insulin levels indicate that obese preadolescent children already have hyperinsulinemia with insulin resistance affecting glucose and lipid metabolism (28). Racial differences, especially relating to decreased hepatic clearance of insulin, may be relevant (29). In a cohort of 228 obese Japanese children in a single prefecture, hyperinsulinemia was found in 32% and by regression analysis appeared to be the major contributor to occurrence of elevated serum ALT, used as a marker for NASH (30). A recent study in obese adolescents documented hyperinsulinemia as well as perturbations to insulin-like growth factor I and its binding proteins (31).
Although chronic hyperinsulinemia coupled with hepatocellular insulin resistance may be important for development of NASH, genetic differences unrelated to carbohydrate and lipid metabolism may account for the heterogeneity of clinical findings in NASH. These include heterozygosity for the HFE gene (32), α1-antitrypsin phenotype (33), adequacy of anti-oxidant defenses such as hepatic glutathione levels, and hepatic cytochrome P450. Hepatocellular concentrations of CYP2E1, an ethanol-inducible cytochrome P450 that activates some xenobiotics to toxic intermediates, were found to be increased in adults with NASH (34). Genes regulating body weight, such as the ob gene (35), may also play a role in the clinical diversity of NASH.
The long-term prognosis of children with NASH remains unknown. In adults, weight reduction can lead to improvement in serum aminotransferase levels (36,37). All six patients in our series who lost weight had a decrease in serum aminotransferases. Although the number was small, the trend was toward improvement. In the series of obese children reported by Vajro et al. (11) persistently elevated aminotransferases normalized in all seven patients after weight reduction, and liver size decreased in those with hepatomegaly. In the only patient in that series with steatohepatitis detected in liver biopsy at diagnosis, inflammation resolved after weight reduction. A more recent report of 38 obese children with fatty liver diagnosed by sonography documents that the liver sonogram improved or became normal in 26 (79%) of the 33 children who lost weight when assessed at 3 months of age. All children who had had elevated aminotransferases had normal aminotransferases at that time (15). Whether improvement in aminotransferase levels always parallels improvement in liver histology is not known, because serial liver biopsies are rarely performed. However, until results of long-term follow-up studies are available in children, it is prudent to recommend a weight loss program for these obese children. We use a combination of energy intake restriction, mainly by reducing fat intake, and increased energy expenditure through aerobic exercise. Other possible treatments include ursodeoxycholic acid (38) or antioxidants such as vitamin E (39), but such treatments have not been evaluated rigorously.
We conclude that NASH is not limited to adults. Indeed, it may be fairly common in children. It should certainly be suspected in obese children with mildly elevated serum aminotransferases. Moreover, it can occur in nonobese children. Sonography may suggest the diagnosis of massive fatty infiltration in the liver, but a liver biopsy is needed to assess the degree of chronic damage. Steatohepatitis can be found in other diseases affecting the liver. Wilson disease must be excluded. Chronic viral hepatitis and drug-induced hepatitis must also be considered in the differential diagnosis. Not necessarily a benign disorder, NASH can progress to cirrhosis during childhood and may account for some cases of cirrhosis in adults in whom the cause is obscure. Although there may be diverse causes for NASH in children, we believe that many children have specific and potentially definable disorders of hepatocellular metabolism.
Dr. Rashid was supported by a Duncan Gordon Fellowship from the Hospital for Sick Children Foundation and a grant from Janssen Pharmaceutica. This report is dedicated to the memory of James L. Weber, MD, FRCPC, distinguished paediatrician and liver specialist, in appreciation of his mentorship.
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Keywords:© 2000 Lippincott Williams & Wilkins, Inc.
Acanthosis nigricans; Fatty liver; Fibrosis; Obesity; Steatohepatitis