Background/Aims: Metabolic dysfunction-associated steatotic liver disease (MASLD) was recently proposed as an alternative disease concept to nonalcoholic fatty liver disease (NAFLD). We aimed to investigate the prognosis of patients with biopsy-confirmed MASLD using data from a multicenter study. Methods: This was a sub-analysis of the Clinical Outcome Nonalcoholic Fatty Liver Disease (CLIONE) study that included 1,398 patients with NAFLD. Liver biopsy specimens were pathologically diagnosed and histologically scored using the NASH Clinical Research Network system, the FLIP algorithm, and the SAF score. Patients who met at least one cardiometabolic criterion were diagnosed with MASLD. Results: Approximately 99% of cases (n=1,381) were classified as MASLD. Patients with no cardiometabolic risk (n=17) had a significantly lower BMI than patients with MASLD (20.9 kg/m2 vs. 28.0 kg/m2, P<0.001), in addition to significantly lower levels of inflammation, ballooning, NAFLD activity score, and fibrosis stage based on liver histology. These 17 patients had a median follow-up of 5.9 years, equivalent to 115 person-years, with no deaths, liver-related events, cardiovascular events, or extrahepatic cancers. The results showed that the prognosis for pure MASLD was similar to that for the original CLIONE cohort, with 47 deaths and one patient who underwent orthotopic liver transplantation. The leading cause of death was extrahepatic cancer (n=10), while the leading causes of liver-related death were liver failure (n=9), hepatocellular carcinoma (n=8), and cholangiocarcinoma (n=4). Conclusions Approximately 99% of NAFLD cases were considered MASLD based on the 2023 liver disease nomenclature. The NAFLD-only group, which is not encompassed by MASLD, had a relatively mild histopathologic severity and a favorable prognosis. Consequently, the prognosis of MASLD is similar to that previously reported for NAFLD.

The patient was a 68-year-old man. In January 2017, he underwent aortic valve replacement (Carpentier-Edwards Perimount Magna, 25 mm, Edwards Lifescience Corporation, Irvine, USA) for aortic stenosis and coronary bypass surgery with two saphenous vein grafts (SVG-#7 and SVG-4PD) for asymptomatic myocardial ischemia. He was treated as an outpatient by a local physician for at least a week during November 2017, with a principal complaint of mild fever, but no other significant symptoms. Transthoracic echocardiography suggested prosthetic valve endocarditis, so he was referred to the author's hospital. The day after admission, he had symptoms of thoracic discomfort, and emergency cardiac catheter examination showed a lesion thought to be due to a thrombus in the left main coronary trunk ; so, thrombus aspiration was carried out. However, no improvement in blood flow was achieved, so balloon angioplasty was carried out, with the aim of improving blood flow in the left circumflex artery, where coronary artery bypass grafting had not been performed. Improvement in blood flow was achieved, and a culture was carried out using the aspirated thrombus. Streptococcus pasteurianus was detected in the culture.