Pathologic Diagnosis of Nonalcoholic Fatty Liver Disease

• Context.—Nonalcoholic fatty liver disease (NAFLD) encompasses steatosis and steatohepatitis. The cause may be multifactorial, and diagnosis requires correlation with clinical information and laboratory results. Objective.—To provide an overview of the status of histology diagnosis of steatosis, steatohepatitis, and associated conditions. Data Sources.—A literature search was performed using the PubMed search engine. The terms ‘‘steatosis,’’ ‘‘steatohepatitis,’’ ‘‘nonalcoholic fatty liver disease (NAFLD),’’ ‘‘nonalcoholic steatohepatitis (NASH),’’ ‘‘alcoholic steatohepatitis (ASH),’’ ‘‘type 2 diabetes (T2DM),’’ ‘‘cryptogenic cirrhosis,’’ ‘‘drug-induced liver injury (DILI),’’ ‘‘immune checkpoint inhibitor therapy,’’ and ‘‘COVID-19 and liver’’ were used. Conclusions.—Nonalcoholic fatty liver disease has become the most common chronic liver disease in the United States. NASH is the progressive form of nonalcoholic fatty liver disease. The hallmarks of steatohepatitis are steatosis, ballooned hepatocytes, and lobular inflammation. NASH and alcoholic steatohepatitis share similar histologic features, but some subtle differences may help their distinction. NASH is commonly seen in patients with metabolic dysfunction but can also be caused by other etiologies. Examples are medications including newly developed immune checkpoint inhibitors and viral infections such as coronavirus disease 2019 (COVID-19). NASH is also a common cause of cryptogenic cirrhosis but can be reversed. The results from recent clinical trials for NASH treatment are promising in reducing the severity of steatosis, ballooning, and fibrosis.