What are the diagnostic criteria for muscle saropenia?

Diagnosis of Muscle Sarcopenia

The gold standard for diagnosing sarcopenia is computed tomography (CT) imaging at the L3 vertebra to quantify skeletal muscle mass, with established cut-off values of <50 cm²/m² for men and <39 cm²/m² for women. 1

Definition and Prevalence

Sarcopenia is defined as a progressive and generalized loss of skeletal muscle mass, strength, and physical performance below a defined threshold 2. It affects:

• 30-70% of patients with end-stage liver disease 1
• More men (54%) than women (21%) with cirrhosis awaiting liver transplantation 1
• 17-40% of children with end-stage liver disease 1

Diagnostic Approach

Primary Assessment Methods

1. Cross-sectional imaging (Gold Standard):

   • CT scan at L3 vertebra: Measures total skeletal muscle area normalized to height (skeletal muscle index, SMI) 1
   • Cut-off values: <50 cm²/m² for men and <39 cm²/m² for women 1
   • Advantages: Highly specific, can evaluate both muscle quantity and quality 3
   • Limitations: Cost, radiation exposure, limited availability 1, 3

2. Anthropometric measurements:

   • Mid-arm muscle circumference (MAMC): Calculated as mid-arm circumference minus [triceps skinfold (TSF) × 0.314] 1
   • Mid-arm muscular area (MAMA): Calculated as MAMC/4×0.314 1
   • Advantages: Simple, rapid, low cost, not affected by fluid retention 1
   • Limitations: Requires trained personnel, less accurate than imaging 1

3. Bioelectrical impedance analysis (BIA):

   • Measures: Fat-free mass and phase angle 1
   • Advantages: Portable, less expensive than imaging, suitable for community settings 4
   • Limitations: Affected by fluid retention, limited availability of devices 1

4. Dual-energy X-ray absorptiometry (DEXA):

   • Measures: Appendicular skeletal muscle mass 5, 3
   • Advantages: Accurate, widely available, established cut-off values 3
   • Limitations: Limited by fluid retention in certain body compartments 1

Functional Assessment (Required for Complete Diagnosis)

1. Muscle strength assessment:

   • Handgrip dynamometry: Measures isometric strength 1, 2
   • Knee extension strength: Correlates well with CT-measured muscle mass 6

2. Physical performance tests:

   • Gait speed: <0.8 m/s indicates impairment 1, 2
   • Timed-Up and Go test (TUG): Measures functional mobility 4
   • Standing-up test: Correlates with muscle mass and quality 6

Diagnostic Algorithm

1. Initial screening: SARC-F questionnaire (5 questions about strength, walking ability, rising from chair, stair climbing, and falls) 4

2. If positive screening or clinical suspicion:

   • Assess muscle strength using handgrip dynamometry 2
   • If strength is reduced, proceed to muscle mass assessment

3. Muscle mass assessment:

   • If CT scan is available (from previous imaging): Measure SMI at L3 1
   • If no CT available: Use MAMC/anthropometrics or BIA 1, 4

4. Physical performance assessment:

   • Gait speed test (<0.8 m/s indicates impairment) 1
   • Timed-Up and Go test or standing-up test 4, 6

5. Diagnosis confirmation:

   • Sarcopenia: Low muscle mass plus low muscle strength 1, 2
   • Severe sarcopenia: Low muscle mass, low strength, and low physical performance 2

Special Considerations

• Sarcopenic obesity: Decreased muscle mass with increased fat mass, affecting 20-35% of patients with cirrhosis 1
• Sex differences: Cut-off values and prevalence differ between men and women 1
• Fluid retention: Can affect accuracy of BIA and anthropometric measurements 1
• Pediatric assessment: CT imaging with quantitative morphomics provides the most accurate assessment in children 1

Clinical Implications

• Sarcopenia predicts mortality both before and after liver transplantation 1
• Associated with hepatic decompensation, reduced quality of life, increased infection risk, and prolonged hospitalization 1
• In children, associated with growth failure, hospitalizations, infections, and motor delay 1

By following this diagnostic approach, clinicians can accurately identify sarcopenia and implement appropriate interventions to improve patient outcomes.