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GERICLINICS

GeriQBank · Paper III · Q4

Sarcopenia — Aetiology, Pathogenesis and Evaluation

Very High YieldAsked ×315-mark essay + 7-mark note
Topic
Frailty & Sarcopenia
Chapter
Frailty, Sarcopenia, Deconditioning & Biology of Ageing
Years asked
Not recorded in the source
Frequency
Set 3× in Paper III (2009–2025)

As set in the university paper

  • Sarcopenia in the elderly — etiology, pathogenesis and evaluation.

    Paper III · Geriatric Assessment, Frailty & Sarcopenia · asked ×3 · 15-mark essay + 7-mark note · see in paper list

Answer framework

  1. Definition and epidemiology — definition, prevalence, dynapenia, sarcopenic obesity, myosteatosis
  2. Aetiology — early life, genetics, predictors, vitamin D, disease
  3. Pathogenesis — testosterone, myostatin, motor units, cytokines, vascular and metabolic factors; anabolic versus catabolic pathways
  4. Evaluation — measuring muscle mass; operational definitions; biomarkers; EWGSOP2 and AWGS algorithms and cut-offs
  5. Treatment outline — resistance exercise, protein, vitamin D
  6. Recent updates — GLIS 2024, Asian cut-offs, Indian data, nutrition targets, drugs, GLP-1 agonists, CT-based measurement

An exam answer plan drawn from the detailed answer below. Use it to attempt the question first.

Detailed answer

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Attempt it firstOutline your answer as a 15-mark essay + 7-mark note before revealing it — definition, causes, evaluation, management and the geriatric angle.Reveal answer

Short revision answer

  • Sarcopenia is the age-related loss of muscle mass (with strength and function): 13–24% at 60–70 and about 50% over 80. Dynapenia is loss of strength; sarcopenic obesity has the worst outcomes.
  • Causes: early life (birth weight), genes, low energy intake and activity, low IGF-1 and testosterone, cytokines, vitamin D deficiency, and disease (heart failure, COPD, diabetes, CKD, cancer).
  • Testosterone falls about 1% a year from 30 and drives satellite cells; myostatin (via the activin IIb receptor) restrains growth; TNF-α and IL-6 reduce strength; motor unit firing falls after 80.
  • Final common pathway: anabolic IGF-1/PI3K/AKT/mTOR signalling loses out to catabolic FOXO → atrogin-1 and MuRF1 → ubiquitin–proteasome breakdown.
  • Measure appendicular skeletal muscle mass by DXA divided by height squared (ASMI); MRI, CT, BIA and ultrasound are alternatives.
  • EWGSOP2: SARC-F ≥4 → strength (grip <27 kg men, <16 kg women, or five chair stands >15 s) → mass (ASMI <7.0 / <5.5 kg/m²) → severity (gait speed ≤0.8 m/s, SPPB ≤8, TUG ≥20 s).
  • For Indian patients use AWGS 2019: grip <28 / <18 kg; ASMI by DXA <7.0 / <5.4; gait speed <1.0 m/s. "Possible sarcopenia" lets treatment start before DXA is available.
  • GLIS 2024: a muscle disease with low muscle mass as the cardinal feature, distinct from frailty, cachexia and malnutrition; ICD-10 code M62.84.
  • Treatment: progressive resistance exercise plus protein 1.0–1.5 g/kg/day (25–30 g per meal) and vitamin D; there is no approved drug.

Condensed by GeriClinics from the detailed answer below, with no new facts added.

15–20 High-Yield Points (Textbook)

A. Definition and Epidemiology

1.

Sarcopenia is the excessive loss of muscle mass that occurs in older people, usually defined as lean tissue more than two standard deviations below that of young reference subjects.

2.

It occurs in 13–24% of people aged 60–70 years and in about 50% of those over 80 years.

3.

Dynapenia is the age-associated loss of muscle strength not due to disease — the counterpart of sarcopenia, which refers to loss of mass. Both progress with ageing.

4.

Sarcopenic obesity ("fat frail") describes those who lose muscle while retaining fat; longitudinally they have the highest risk of disability and mortality.

5.

Myosteatosis — fat infiltration into muscle — is a separate condition linked to insulin resistance: mitochondrial failure or high circulating triglycerides cause intracellular triglyceride accumulation, which alters insulin receptor substrate function and the GLUT transporter.

B. Aetiology

6.

Sarcopenia may originate at birth: in the Hertfordshire cohort study adult grip strength correlated with birth weight.

7.

Genetic factors: people with a single I or double I allele of the angiotensin-converting enzyme gene generate more power with regular exercise than those with the D allele. Genome-wide studies implicate HSD17B11, VCAN, ADAMTSL3, IRS1 and FTO.

8.

The best epidemiological predictors of muscle mass and strength are age, energy intake, physical activity, IGF-1, testosterone and cytokines.

9.

Hypovitaminosis D is associated with reduced muscle strength and falls.

10.

Disease-related contributors are the same as for frailty: heart failure, COPD, diabetes, chronic kidney disease, anaemia, cancer cachexia and inflammatory disease.

C. Pathogenesis

11.

Testosterone declines by about 1% per year from age 30 in men and falls rapidly between ages 20 and 40 in women. It inhibits movement of pluripotential stem cells into the fat cell lineage and stimulates the muscle cell lineage to produce satellite cells, which are essential for repair.

12.

Testosterone also stimulates muscle protein synthesis and inhibits the ubiquitin–proteasome pathway; replacement increases muscle mass, strength, power and function even in non-hypogonadal men.

13.

Myostatin is the principal negative regulator of muscle growth, acting through activin IIb receptors. Double deletion produces marked hypertrophy in mice ("mighty mouse"), cattle, whippets and one reported human; a soluble activin IIb receptor scavenges the ligand and produces muscle and bone hypertrophy.

14.

Motor unit dysfunction: firing rate falls significantly in the old-old (over 80). Ciliary neurotrophic factor (CNTF) declines with age in parallel with strength. C-terminal agrin fragment and neurofilament light chain, markers of neural degradation, are raised in a subset of sarcopenic patients.

15.

Cytokines: excess TNF-α and IL-6 cause loss of muscle strength; high CRP and IL-6 correlate with reduced grip strength and physical performance.

16.

Vascular and metabolic factors: raised homocysteine and peripheral vascular disease impair muscle blood flow causing atrophy; creatine with exercise may improve performance.

17.

The final common pathway is an imbalance of the daily muscle renewal cycle — either excess atrophy and apoptosis, or reduced hypertrophy and satellite cell production.

18.

Biochemistry (Pathy Fig 97.7) — Anabolic arm: GH / testosterone / creatine → IGF-1 and mechano-growth factor → PI3K → AKT → mTOR → S6K1 → hypertrophy. Catabolic arm: glucocorticoids, cytokines (TNF receptor I → IKK → NF-κB), and inactive AKT → FOXO → atrogin-1 (MAFbx) and MuRF1 → ubiquitin–proteasome protein degradation → atrophy. Myostatin–SMAD3 inhibits MyoD; caspase-3 and caspase-8 mediate apoptosis and actomyosin cleavage.

D. Evaluation

19.

The best measure is appendicular skeletal muscle mass by DXA divided by height in metres squared. Alternatives are MRI, CT and bioelectrical impedance; DXA and MRI correlate highly, and ultrasound is proving an excellent measure of muscle loss. MRI is superior for visceral compartments, muscle volume, fat infiltration and ectopic fat; BIA is the most accessible in primary care but is only an approximation, better for limbs than trunk.

20.

Several operational definitions exist — FNIH Biomarkers Consortium, EWGSOP and AWGS — and they differ in cut-offs and severity grading, but all agree on including muscle strength, muscle mass and physical performance.

21.

Candidate biomarkers: procollagen type III N-terminal peptide (P3NP), D3-creatine dilution (correlates highly with MRI muscle mass), C-terminal agrin fragment, myostatin and follistatin, GDF-11 and GDF-15, and leptin in sarcopenic obesity. None is validated alone.

22.

Treatment, as given in the frailty chapter, is resistance exercise plus protein 1 g/kg/day, correction of vitamin D deficiency, treatment of underlying disease, and consideration of testosterone or SARMs.

Extra Points to Remember (Recurring Topic)

Learn the three-word definition triad: mass + strength + performance. Any answer that mentions only muscle mass loses marks.

Distinguish clearly: sarcopenia (mass), dynapenia (strength), myosteatosis (fat within muscle), cachexia (inflammation-driven loss of lean ± fat mass in advanced disease), sarcopenic obesity (worst prognosis). Primary sarcopenia = age-related only. Secondary sarcopenia = disease-related, inactivity-related or nutrition-related. Acute sarcopenia = under 6 months, typically after hospitalisation; chronic = 6 months or more. Be able to draw the anabolic (IGF-1/PI3K/AKT/mTOR) versus catabolic (FOXO/atrogin-1/MuRF1/ubiquitin-proteasome) diagram — it answers "pathogenesis" in one figure.

The single most examinable formula: ASMI = appendicular skeletal muscle mass (kg) / height (m)2. Sarcopenia has an ICD-10 code (M62.84) — it is now formally a disease, not a normal ageing change.

Latest Updates (2023–Present)

GLIS — Global Leadership Initiative in Sarcopenia (Delphi consensus, Age and Ageing 2024) produced the first global conceptual definition, uniting EWGSOP, AWGS, ANZSSFR, SDOC and the sarcopenic obesity group. Key conclusions: sarcopenia is a muscle disease; low muscle mass is the cardinal, mandatory feature; muscle strength and muscle-specific function (function attributable to muscle rather than general physical performance) are the other components; and sarcopenia is conceptually distinct from frailty, cachexia and malnutrition. The GLIS outcomes working group consensus (2025) defined the health outcomes that should be measured once sarcopenia is diagnosed — falls, fractures, disability, hospitalisation, quality of life and mortality — and the preferred tools and cut-offs. A single global operational definition with numerical cut-offs is still pending. EWGSOP2 algorithm (Find–Assess–Confirm–Severity) remains the working clinical pathway: SARC-F questionnaire ≥4 → assess strength (grip <27 kg men, <16 kg women; or five-times chair stand >15 s) → confirm with muscle mass (ASMI by DXA <7.0 kg/m2 men, <5.5 kg/m2 women) → grade severity by performance (gait speed ≤0.8 m/s, SPPB ≤8, TUG ≥20 s, 400 m walk test).

AWGS 2019 Asian cut-offs are the appropriate ones for Indian patients: grip <28 kg men, <18 kg women; ASMI by DXA <7.0 / <5.4 kg/m2, by BIA <7.0 / <5.7 kg/m2; gait speed <1.0 m/s; five-times chair stand ≥12 s. AWGS also introduced "possible sarcopenia" for primary care, allowing lifestyle intervention to start before DXA is available — important given limited DXA access in India.

Indian community studies report sarcopenia prevalence of roughly 17–25% in community-dwelling elders and higher in hospital and nursing home populations, with a substantial contribution from low dietary protein intake in largely cereal-based diets.

Nutrition: current targets are 1.0–1.5 g/kg/day of protein, distributed as 25–30 g of high-quality protein per meal, with leucine-enriched essential amino acids or HMB where intake is inadequate, plus correction of vitamin D deficiency. Network meta-analyses (2025) confirm that resistance exercise plus protein supplementation is superior to either alone.

Pharmacotherapy remains investigational: myostatin and activin pathway agents (bimagrumab, apitegromab), SARMs, and testosterone have improved lean mass without convincing functional gains. A new practical concern is preservation of muscle mass during GLP-1 receptor agonist weight loss, where up to 40% of weight lost may be lean mass — muscle-sparing strategies are an active research area.

Sarcopenia is increasingly measured opportunistically from CT scans at the L3 vertebral level (skeletal muscle index), used as a prognostic marker in oncology and before major surgery.

Current Practice Update

Issue Textbook (Pathy 6e) Current Evidence (2023–present)

Definition Loss of muscle mass more than 2 SD below young GLIS 2024: a muscle disease requiring low adults muscle mass (cardinal) + low strength + impaired muscle-specific function Diagnostic entry point Muscle mass measurement (DXA) Muscle strength first (EWGSOP2 / AWGS), mass used to confirm; SARC-F for case-finding Cut-offs Not specified numerically EWGSOP2 grip <27/<16 kg; AWGS <28/<18 kg for Asians; ASMI <7.0/<5.4–5.5 kg/m2 Relation to frailty Overlapping; "two sides of the same coin" Formally distinct entities with separate pathways (GLIS)

Protein target 1 g/kg/day 1.0–1.5 g/kg/day, 25–30 g per meal, leucine-enriched supplements Drug therapy Testosterone and SARMs discussed favourably No approved drug; myostatin/activin agents in trials; focus shifted to exercise and nutrition Disease status Described as a geriatric syndrome Recognised disease with ICD-10 code M62.84 Exam One-Liners Prevalence: 13–24% at 60–70 years, ~50% over 80 years.

ASMI = appendicular skeletal muscle mass / height2, measured by DXA.

Testosterone falls 1% per year after 30; drives satellite cell production.

Myostatin acts via activin IIb receptor; blockade causes hypertrophy.

Atrophy genes = atrogin-1 (MAFbx) and MuRF1, activated by FOXO and NF-κB.

Screening questionnaire = SARC-F; score ≥4 is positive.

Indian/Asian grip cut-offs (AWGS) = 28 kg men, 18 kg women.

Treatment = progressive resistance exercise + protein 1.0–1.5 g/kg/day + vitamin D.

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