What are the differences between metabolic dysfunction‑associated steatohepatitis (MASH) and non‑alcoholic steatohepatitis (NASH) regarding definition, diagnosis, and management?

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Last updated: September 26, 2026 • View editorial policy

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MASH and NASH Are the Same Disease—Just Different Names

MASH (metabolic dysfunction-associated steatohepatitis) and NASH (non-alcoholic steatohepatitis) refer to the identical clinical entity; MASH is simply the updated 2023 nomenclature that replaced NASH. The renaming reflects a paradigm shift toward recognizing the central role of metabolic dysfunction rather than defining the disease by what it is not (non-alcoholic) 1, 2.

Why the Name Changed

The terminology evolved from NASH to MASH as part of a broader reclassification:

  • NAFLD → MASLD (metabolic dysfunction-associated steatotic liver disease)
  • NASH → MASH (metabolic dysfunction-associated steatohepatitis)

This change emphasizes the positive diagnostic criteria of cardiometabolic dysfunction rather than the exclusionary criterion of alcohol intake 1, 2.

Definition (Identical for Both Terms)

Both NASH and MASH describe the inflammatory, progressive form of metabolic steatotic liver disease, characterized by:

  • Hepatic steatosis (fat accumulation)
  • Lobular inflammation
  • Hepatocellular ballooning (hepatocyte injury)
  • With or without fibrosis

This distinguishes it from simple steatosis (MASL/metabolic dysfunction-associated steatotic liver), which lacks inflammation and ballooning 2, 3, 4.

Diagnostic Criteria (No Change)

The diagnostic approach remains identical whether using NASH or MASH terminology:

Required Elements:

  1. Hepatic steatosis confirmed by imaging or histology
  2. At least one cardiometabolic risk factor:
    • BMI ≥25 kg/m² (≥23 kg/m² in Asians) OR waist circumference above ethnic thresholds
    • Fasting glucose ≥100 mg/dL or type 2 diabetes or treatment for hyperglycemia
    • Blood pressure ≥130/85 mmHg or antihypertensive treatment
    • Triglycerides ≥150 mg/dL or lipid-lowering treatment
    • HDL-C <40 mg/dL (men) or <50 mg/dL (women) or lipid-lowering treatment
  3. Absence of harmful alcohol intake (<20 g/day women, <30 g/day men)
  4. Exclusion of other liver diseases (viral hepatitis, autoimmune, drug-induced, etc.)

Histological Confirmation (Gold Standard):

  • Steatosis affecting >5% of hepatocytes
  • Lobular inflammation
  • Hepatocyte ballooning
  • Fibrosis staging (F0-F4) 1, 5

Management (Identical Regardless of Terminology)

Risk Stratification Algorithm:

  1. Initial screening with FIB-4 score in all patients with cardiometabolic risk factors
  2. If FIB-4 indeterminate or high: proceed to vibration-controlled transient elastography
  3. Advanced fibrosis (≥F2): requires intensified treatment and specialist referral 1, 6, 7

Treatment Approach:

Lifestyle Modification (First-Line for All):

  • Weight loss target: ≥5% body weight (≥7-10% for fibrosis regression)
  • Physical activity: ≥150 minutes/week moderate aerobic exercise
  • Dietary changes: Mediterranean diet pattern preferred
  • Alcohol: discourage in mild fibrosis, complete abstinence in significant fibrosis (≥F2) 1, 2, 6

Pharmacotherapy:

For Cardiometabolic Comorbidities:

  • GLP-1 receptor agonists (semaglutide, tirzepatide) for type 2 diabetes or obesity—demonstrated significant liver fat reduction 1, 6, 3

For MASH-Specific Treatment:

  • Resmetirom (THR-β agonist): FDA-approved March 2024 for non-cirrhotic MASH with significant fibrosis (stage ≥F2)
    • Demonstrated histological improvement in steatohepatitis and fibrosis
    • Not recommended for cirrhotic stage 1, 2, 6, 5, 4

Bariatric Surgery:

  • Consider in patients with obesity meeting surgical criteria
  • Achieves MASH resolution in 56-70% of cases 1, 3

Critical Clinical Pitfalls

Do not:

  • Continue using "NASH" or "NAFLD" in documentation—update to MASH/MASLD for consistency with current guidelines 1, 2
  • Assume simple steatosis is benign—fibrosis stage, not inflammation alone, predicts mortality 1, 7, 8
  • Prescribe resmetirom for cirrhotic MASH—no evidence of benefit and not indicated 1, 5
  • Overlook cardiovascular risk—MASLD patients have higher cardiovascular mortality than liver-related mortality 2, 8

Do:

  • Focus on fibrosis stage as the primary prognostic factor and treatment trigger 1, 6, 7
  • Screen high-risk populations (type 2 diabetes, obesity with metabolic risk factors) using sequential non-invasive testing 1, 6
  • Optimize cardiometabolic medications (GLP-1 agonists, SGLT2 inhibitors) before considering liver-directed therapy 1, 2
  • Monitor for hepatocellular carcinoma in cirrhotic patients regardless of whether cirrhosis regresses 1, 5

The Bottom Line

The transition from NASH to MASH represents nomenclature modernization, not a change in disease entity, diagnosis, or management. The histological features, diagnostic criteria, risk stratification approach, and treatment algorithms remain identical. The new terminology simply provides a more accurate, positive diagnostic framework that emphasizes the metabolic dysfunction driving the disease process 1, 2.

References

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