USMLE – Steatosis
Mild steatosis involving less than 10% of hepatocytes is normal: more severe steatosis is seen in a number of other conditions. It is often detected incidentally and its clinical manifestations are very variable.
Steatosis may be macrovesicular where a single fat globule fills the liver cell and pushes the nucleus to the periphery or microvesicular where small fat vacuoles give the liver cell a foamy appearance and the nucleus remains central. Macrovesicular steatosis, with or without some microvesicular steatosis is common and generally benign. Microvesicular steatosis occurs in more serious conditions and can he associated with mitochondrial damage which causes impaired oxidative metabolism. Steatosis is usually not associated with any inflammatory infiltrate or fibrosis within the liver. However, in some patients macrovesicular steatosis occurs with associated neutrophilic infiltrate, liver cell death and, rarely, Mallory’s hyaline. This histological change has been termed steatohepatitis. Steatohepatitis may be caused by alcohol abuse; however, in some patients with other causes there is no history of excessive alcohol consumption. Such patients have so called non-alcoholic steatohepatitis or NASH.
Clinical features and management
Macrovesicular steatosis is often asymptomatic or is associated with the clinical features of its cause, such as diabetes mellitus. It is therefore often found incidentally. Hepatomegaly sometimes with hepatic tenderness is the only clinical feature. Liver function tests usually show mild non-specific abnormalities and ultrasonography shows generally increased echogenicity (bright liver). The treatment is that of the underlying disorder. Ursodeoxycholic acid may improve the liver function tests and the histological appearances in patients with non-alcoholic steatohepatitis (NASH).
Microvesicular steatosis may be associated with the acute onset of fatigue and vomiting, progressing if severe to encephalopathy and coma. Jaundice occurs with fatty liver of pregnancy, alcohol and sometimes drug-induced steatosis, but is typically absent in Reye’s syndrome. Acute hepatic failure due to microvesicular steatosis may require intensive care support or emergency liver transplantation.
The outlook for most patients with steatosis is excellent, although a few deaths have been reported. In patients with alcoholic steatosis, the severity of the fatty change can predict the eventual progression to cirrhosis. Previously, the prognosis of patients with acute fatty liver of pregnancy was considered poor. However, milder forms of this condition are now more frequently recognized.