The classification of sarcopenia is a crucial step for clinicians to accurately diagnose and manage this progressive muscle disease. Sarcopenia, characterized by the progressive loss of skeletal muscle mass and strength, is officially recognized with an ICD-10 code (M62.84). Classification can be broken down into two primary systems: one based on etiology (cause) and another based on severity.
Classification by Etiology: Primary vs. Secondary
The most straightforward way to classify sarcopenia is by its underlying cause. This helps healthcare providers understand the contributing factors and develop more targeted interventions.
Primary (Age-Related) Sarcopenia
Primary sarcopenia occurs when aging is the only identifiable cause of muscle loss. While the natural aging process is the main driver, it is often a complex, multi-factorial geriatric syndrome. Contributing factors include hormonal changes, increased inflammation, and changes in the neuromuscular system. The decline is often gradual but accelerates with increasing age, typically becoming more evident after 70.
Secondary Sarcopenia
Secondary sarcopenia is diagnosed when other factors besides normal aging are the primary cause. This type is further subdivided based on the contributing cause:
- Activity-Related: Caused by a sedentary lifestyle, immobility due to injury or illness, or deconditioning from bed rest.
- Disease-Related: Linked to underlying diseases, such as chronic heart failure, chronic obstructive pulmonary disease (COPD), cancer, or advanced kidney or liver disease. These conditions can trigger systemic inflammation and catabolic processes that break down muscle tissue.
- Nutrition-Related: Results from inadequate dietary intake of energy and/or protein, which is common in older adults due to reduced appetite, difficulty chewing, or malabsorption issues.
Classification by Severity: Staging Models (EWGSOP2)
In addition to classifying by cause, modern clinical guidelines stage sarcopenia based on its severity using diagnostic algorithms. The European Working Group on Sarcopenia in Older People (EWGSOP) published updated criteria in 2019 (EWGSOP2) that provide a clear pathway for staging. The stages are defined by a combination of muscle strength, muscle quantity/quality, and physical performance.
- Probable Sarcopenia: The initial finding is low muscle strength. Clinicians can screen for this using a simple handgrip strength test or the chair stand test. A positive screening indicates probable sarcopenia.
- Confirmed Sarcopenia: The diagnosis is confirmed when both low muscle strength and low muscle quantity or quality are present. Muscle mass is typically measured using tools like Dual-energy X-ray Absorptiometry (DXA) or Bioelectrical Impedance Analysis (BIA).
- Severe Sarcopenia: This is the most advanced stage, diagnosed when all three criteria are met: low muscle strength, low muscle quantity/quality, and poor physical performance. Physical performance is assessed with tests like the gait speed test or the Short Physical Performance Battery (SPPB).
Comparison of EWGSOP2 and AWGS Criteria
Different working groups around the world have developed specific diagnostic criteria and cut-off points, leading to variations in reported prevalence rates. The Asian Working Group for Sarcopenia (AWGS), for instance, has updated its criteria to better suit Asian populations. The following table highlights some of the differences between EWGSOP2 and the AWGS 2019 consensus for diagnosis.
| Assessment Category | EWGSOP2 Criteria | AWGS 2019 Criteria |
|---|---|---|
| Screening | SARC-F score ≥ 4 | SARC-F ≥ 4 OR SARC-CalF ≥ 11 OR Calf Circumference (<34 cm men, <33 cm women) |
| Low Muscle Strength | Handgrip strength: <27kg (men), <16kg (women) | Handgrip strength: <28kg (men), <18kg (women) |
| Low Muscle Mass (DEXA) | Appendicular Lean Mass (ALM)/ht2: <7.0 kg/m² (men), <5.5 kg/m² (women) | ALM/ht2: <7.0 kg/m² (men), <5.4 kg/m² (women) |
| Low Physical Performance | Gait speed ≤ 0.8 m/s OR SPPB ≤ 8 points OR Chair stand > 15s for 5 stands | Gait speed < 1.0 m/s OR SPPB ≤ 9 OR 5-time chair stand ≥ 12s |
| Severity | Severe sarcopenia is diagnosed with low strength, low mass/quality, AND low performance. | Similar criteria; defined as having low muscle strength, mass, and performance. |
Distinguishing Sarcopenia from Other Conditions
An important aspect of sarcopenia classification is differentiating it from other muscle-wasting syndromes like cachexia and frailty. While there is significant overlap, particularly in the older population, they are distinct syndromes.
- Sarcopenia vs. Cachexia: Cachexia is a more severe wasting syndrome associated with serious underlying illnesses like cancer, heart failure, or COPD. Unlike sarcopenia, which is often stable or slow-progressing, cachexia involves severe weight loss (muscle and fat) and a hypermetabolic state driven by systemic inflammation. Though many cachectic patients are also sarcopenic, the reverse is not always true.
- Sarcopenia vs. Frailty: Frailty is a broader geriatric syndrome characterized by a decline across multiple organ systems, affecting psychological, cognitive, and social functions, in addition to physical limitations. While sarcopenia is a core component of physical frailty, the frailty syndrome includes other criteria like unintended weight loss and exhaustion.
Conclusion
The classification of sarcopenia by both cause (primary and secondary) and severity (probable, confirmed, and severe) provides a systematic framework for clinical assessment and management. Etiological classification helps uncover underlying conditions that require separate treatment, while severity staging assists in monitoring the disease's progression and tailoring interventions. Despite variations in diagnostic criteria between international groups like EWGSOP2 and AWGS, the shared focus remains on evaluating muscle strength, mass, and physical performance. Early identification and classification are crucial for initiating appropriate lifestyle interventions, such as resistance training and nutritional support, which can help slow progression and improve the quality of life for affected individuals.
For more detailed information on sarcopenia and healthy aging, explore resources from authoritative bodies like the National Institutes of Health.
Source: National Institutes of Health
