Medicine:Sarcopenia

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Short description: Muscle loss due to ageing or immobility
Sarcopenia
1025 Atrophy.png
Difference between a normal muscle and an atrophied muscle
SpecialtyGeriatrics
Rheumatology

Sarcopenia (ICD-10 code M62.84) is a type of muscle loss that occurs with aging and/or immobility. It is characterized by the degenerative loss of skeletal muscle mass, quality, and strength. The rate of muscle loss is dependent on exercise level, co-morbidities, nutrition and other factors. The muscle loss is related to changes in muscle synthesis signalling pathways. It is distinct from cachexia, in which muscle is degraded through cytokine-mediated degradation, although the two conditions may co-exist. Sarcopenia is considered a component of frailty syndrome.[1] Sarcopenia can lead to reduced quality of life, falls, fracture, and disability.[2][3]

Sarcopenia is a factor in changing body composition. When associated with aging populations, certain muscle regions are expected to be affected first, specifically the anterior thigh and abdominal muscles.[2][4] In population studies, body mass index (BMI) is seen to decrease in aging populations while bioelectrical impedance analysis (BIA) shows body fat proportion rising.[5]

Etymology

The term sarcopenia stems from Greek σάρξ sarx, "flesh" and πενία penia, "poverty". This was first proposed by Rosenberg in 1989, who wrote that "there may be no single feature of age-related decline that could more dramatically affect ambulation, mobility, calorie intake, and overall nutrient intake and status, independence, breathing, etc".[citation needed]

Sarcopenia is distinct from cachexia, in which muscle is degraded through cytokine-mediated degradation, although the two conditions may co-exist.

Signs and symptoms

The hallmark sign of sarcopenia is loss of lean muscle mass, or muscle atrophy. The change in body composition may be difficult to detect due to obesity, changes in fat mass, or edema. Changes in weight, limb or waist circumference are not reliable indicators of muscle mass changes. Sarcopenia may also cause reduced strength, functional decline and increased risk of falling. Sarcopenia may also have no symptoms until it is severe and is often unrecognized.[1] Research has shown, however, that hypertrophy may occur in the upper parts of the body to compensate for this loss of lean muscle mass[2][6] Therefore, one early indicator of the onset of sarcopenia can be significant loss of muscle mass in the anterior thigh and abdominal muscles.[2]

Causes

There are many proposed causes of sarcopenia and it is likely the result of multiple interacting factors. Understanding of the causes of sarcopenia is incomplete, however changes in hormones, immobility, age-related muscle changes, nutrition and neurodegenerative changes have all been recognized as potential causative factors.[7]

The degree of sarcopenia is determined by two factors: the initial amount of muscle mass and the rate at which muscle mass declines. Due to variations in these factors across the population, the rate of progression and the threshold at which muscle loss becomes apparent is variable.[8] Immobility dramatically increases the rate of muscle loss, even in younger people. Other factors that can increase the rate of progression of sarcopenia include decreased nutrient intake, low physical activity, or chronic disease.[1] Additionally, epidemiological research has indicated that early environmental influences may have long-term effects on muscle health. For example, low birth weight, a marker of a poor early environment, is associated with reduced muscle mass and strength in adult life.[9][10][11]

Pathophysiology

There are multiple theories proposed to explain the mechanisms of muscle changes of sarcopenia including changes in myosatellite cell recruitment, changes in anabolic signalling, protein oxidation, inflammation, and developmental factors. The pathologic changes of sarcopenia include a reduction in muscle tissue quality as reflected in the replacement of muscle fibers with fat, an increase in fibrosis, changes in muscle metabolism, oxidative stress, and degeneration of the neuromuscular junction.[12] The failure to activate satellite cells upon injury or exercise is also thought to contribute to the pathophysiology of sarcopenia.[12] Additionally, oxidized proteins can lead to a buildup of lipofuscin and cross-linked proteins causing an accumulation of non-contractile material in the skeletal muscle and contribute to sarcopenic muscle.[8]

In sarcopenic muscle the distribution of the types of muscle fibers changes with a decrease in type II muscle fibers, or "fast twitch," with little to no decrease in type I muscle fibers, or "slow-twitch" muscle fibers. Deinervated type II fibers are often converted to type I fibers by reinnervation by slow type I fiber motor nerves.[13] Males are perhaps more susceptible for this aging-related switching of the myofiber type, as a recent research has shown a higher percentage of "slow twitch" muscle fibers in old compared to young males, but not in old compared to young females.[14]

Aging sarcopenic muscle shows an accumulation of mitochondrial DNA mutations, which has been demonstrated in various other cell types as well.[15] Clones with mitochondrial mutations build up in certain regions of the muscle, which goes along with an about fivefold increase in the absolute mtDNA copy number, that is, these regions are denser.[16] An apparent protective factor preventing cells' buildup of damaged mitochondria is sufficient levels of the protein BNIP3. Deficiency of BNIP3 leads to muscle inflammation and atrophy.[17]

Furthermore, not every muscle is as susceptible to the atrophic effects of aging. For example, in both humans[18] and mice[19] it has been shown that lower leg muscles are not as susceptible to aging as upper leg muscles. This could perhaps be explained by the differential distribution of myofiber type within each muscle group, but this is unknown.

Diagnosis

Multiple diagnostic criteria have been proposed by various expert groups and continues to be an area of research and debate. Despite the lack of a widely accepted definition, sarcopenia was assigned an ICD-10 code (M62.84) in 2016, recognizing it as a disease state.[20]

Sarcopenia can be diagnosed when a patient has muscle mass that is at least two standard deviations below the relevant population mean and has a slow walking speed.[21] The European Working Group on Sarcopenia in Older People (EWGSOP) developed a broad clinical definition for sarcopenia, designated as the presence of low muscle mass and either low muscular strength or low physical performance.[7] Other international groups have proposed criteria that include metrics on walking speed, distance walked in 6 minutes, or grip strength.[20] Hand grip strength alone has also been advocated as a clinical marker of sarcopenia that is simple and cost effective and has good predictive power, although it does not provide comprehensive information.[22]

There are screening tools for sarcopenia that assess patient reported difficulty in doing daily activities such as walking, climbing stairs or standing from a chair and have been shown to predict sarcopenia and poor functional outcomes.[23]

Management

Exercise

Exercise remains the intervention of choice for sarcopenia, but translation of research findings into clinical practice is challenging. The type, duration and intensity of exercise are variable between studies, preventing a standardized exercise prescription for sarcopenia.[24] Lack of exercise is a significant risk factor for sarcopenia and exercise can dramatically slow the rate of muscle loss.[25] Exercise can be an effective intervention because aging skeletal muscle retains the ability to synthesize proteins in response to short-term resistance exercise.[26] Progressive resistance training in older adults can improve physical performance (gait speed) and muscular strength.[27] Increased exercise can produce greater numbers of cellular mitochondria, increase capillary density, and increase the mass and strength of connective tissue.[28]

Medication

There are currently no approved medications for the treatment of sarcopenia.[29] Testosterone or other anabolic steroids have also been investigated for treatment of sarcopenia, and seem to have some positive effects on muscle strength and mass, but cause several side effects and raise concerns of prostate cancer in men and virilization in women.[30][31] Additionally, recent studies suggest testosterone treatments may induce adverse cardiovascular events.[32][33][34]

DHEA and human growth hormone have been shown to have little to no effect in this setting. Growth hormone increases muscle protein synthesis and increases muscle mass, but does not lead to gains in strength and function in most studies.[30] This, and the similar lack of efficacy of its effector insulin-like growth factor 1 (IGF-1), may be due to local resistance to IGF-1 in aging muscle, resulting from inflammation and other age changes.[30]

Other medications under investigation as possible treatments for sarcopenia include ghrelin, vitamin D, angiotensin converting enzyme inhibitors, and eicosapentaenoic acid.[30][31]

Nutrition

Intake of calories and protein are important stimuli for muscle protein synthesis.[35] Older adults may not utilize protein as efficiently as younger people and may require higher amounts to prevent muscle atrophy.[21] A number of expert groups have proposed an increase in dietary protein recommendations for older age groups to 1.0–1.2 g/kg body weight per day.[36][37] Ensuring adequate nutrition in older adults is of interest in the prevention of sarcopenia and frailty, since it is a simple, low-cost treatment approach without major side effects.[38]

Supplements

A component of sarcopenia is the loss of ability for aging skeletal muscle to respond to anabolic stimuli such as amino acids, especially at lower concentrations. However, aging muscle retains the ability of an anabolic response to protein or amino acids at larger doses. Supplementation with larger doses of amino acids, particularly leucine has been reported to counteract muscle loss with aging.[39] Exercise may work synergistically with amino acid supplementation.[29]

β-hydroxy β-methylbutyrate (HMB) is a metabolite of leucine that acts as a signalling molecule to stimulate protein synthesis.[21][29] It is reported to have multiple targets, including stimulating mTOR and decreasing proteasome expression. Its use to prevent the loss of lean body mass in older adults is consistently supported in clinical trials.[40][41][42] More research is needed to determine the precise effects of HMB on muscle strength and function in this age group.[41]

Epidemiology

The prevalence of sarcopenia depends on the definition used in each epidemiological study. Estimated prevalence in people between the ages of 60-70 is 5-13% and increases to 11-50% in people more than 80 years of age. This equates to >50 million people and is projected to affect >200 million in the next 40 years given the rising population of older adults.[7]

Public health impact

Sarcopenia is emerging as a major public health concern given the increased longevity of industrialized populations and growing geriatric population. Sarcopenia is a predictor of many adverse outcomes including increased disability, falls and mortality.[43][44] Immobility or bed rest in populations predisposed to sarcopenia can cause dramatic impact on functional outcomes. In the elderly, this often leads to decreased biological reserve and increased vulnerability to stressors known as the "frailty syndrome". Loss of lean body mass is also associated with increased risk of infection, decreased immunity, and poor wound healing. The weakness that accompanies muscle atrophy leads to higher risk of falls, fractures, physical disability, need for institutional care, reduced quality of life, increased mortality, and increased healthcare costs.[21] This represents a significant personal and societal burden and its public health impact is increasingly recognized.[7]

Research directions

There are significant opportunities to better understand the causes and consequences of sarcopenia and help guide clinical care. This includes elucidation of the molecular and cellular mechanisms of sarcopenia, further refinement of reference populations by ethnic groups, validation of diagnostic criteria and clinical tools, as well as tracking of incidence of hospitalization admissions, morbidity, and mortality. Identification and research on potential therapeutic approaches and timing of interventions is also needed.[45]

(As of 2020), there are no drugs approved to treat muscle wasting in people with chronic diseases, and there is therefore an unmet need for anabolic drugs with few side effects. One aspect hindering drug approval for treatments for cachexia and sarcopenia is disagreement in endpoints. Several clinical trials have found that selective androgen receptor modulators (SARMs) improve lean mass in humans, but it is not clear whether strength and physical function are also improved. After promising results in a phase II trial, a phase III trial of the SARM ostarine was proven to increase lean body mass but did not show significant improvement in function.[46] It and other drugs—such as the growth hormone secretagogue anamorelin—have been refused regulatory approval despite significant increases in lean mass due to a lack of evidence that they increased physical performance. Preventing decline in functionality was not considered an acceptable endpoint by the Food and Drug Administration. It is not known how SARMs interact with dietary protein intake and resistance training in people with muscle wasting.[47][48]

See also


References

  1. ↑ 1.0 1.1 1.2 "Differentiating Sarcopenia and Cachexia Among Patients With Cancer". Nutrition in Clinical Practice 32 (1): 30–39. February 2017. doi:10.1177/0884533616680354. PMID 28124947. 
  2. ↑ 2.0 2.1 2.2 2.3 "Sarcopenia Is Not "Love": You Have to Look Where You Lost it!". American Journal of Physical Medicine & Rehabilitation 99 (10): e119–e120. October 2020. doi:10.1097/PHM.0000000000001391. PMID 32084033. 
  3. ↑ "Health Outcomes of Sarcopenia: A Systematic Review and Meta-Analysis". PLOS ONE 12 (1): e0169548. 2017. doi:10.1371/journal.pone.0169548. PMID 28095426. Bibcode: 2017PLoSO..1269548B. 
  4. ↑ "Regional and total muscle mass, muscle strength and physical performance: The potential use of ultrasound imaging for sarcopenia". Archives of Gerontology and Geriatrics 83: 55–60. 2019. doi:10.1016/j.archger.2019.03.014. PMID 30953961. 
  5. ↑ "Relationship between Body Mass Index (BMI) and body fat percentage, estimated by bioelectrical impedance, in a group of Sri Lankan adults: a cross sectional study". BMC Public Health 13: 797. September 2013. doi:10.1186/1471-2458-13-797. PMID 24004464. 
  6. ↑ "Assessment of core and lower limb muscles for static/dynamic balance in the older people: An ultrasonographic study". Age and Ageing 48 (6): 881–887. November 2019. doi:10.1093/ageing/afz079. PMID 31268513. 
  7. ↑ 7.0 7.1 7.2 7.3 "Sarcopenia: European consensus on definition and diagnosis: Report of the European Working Group on Sarcopenia in Older People". Age and Ageing 39 (4): 412–423. July 2010. doi:10.1093/ageing/afq034. PMID 20392703. 
  8. ↑ 8.0 8.1 "Sarcopenia: causes, consequences, and preventions". The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences 58 (10): M911–M916. October 2003. doi:10.1093/gerona/58.10.m911. PMID 14570858. 
  9. ↑ "Does sarcopenia originate in early life? Findings from the Hertfordshire cohort study". The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences 59 (9): M930–M934. September 2004. doi:10.1093/gerona/59.9.M930. PMID 15472158. 
  10. ↑ "Intrauterine programming of adult body composition". The Journal of Clinical Endocrinology and Metabolism 86 (1): 267–272. January 2001. doi:10.1210/jcem.86.1.7155. PMID 11232011. 
  11. ↑ "Birth size, adult body composition and muscle strength in later life". International Journal of Obesity 31 (9): 1392–1399. September 2007. doi:10.1038/sj.ijo.0803612. PMID 17356523. 
  12. ↑ 12.0 12.1 "Cellular and molecular mechanisms underlying age-related skeletal muscle wasting and weakness". Biogerontology 9 (4): 213–228. August 2008. doi:10.1007/s10522-008-9131-0. PMID 18299960. 
  13. ↑ "Invited review: Aging and sarcopenia". Journal of Applied Physiology 95 (4): 1717–1727. October 2003. doi:10.1152/japplphysiol.00347.2003. PMID 12970377. 
  14. ↑ de Jong, Jelle C.B.C.; Attema, Brecht J; van der Hoek, Marjanne D; Verschuren, Lars; Caspers, Martien P M; Kleemann, Robert; van der Leij, Feike R; van den Hoek, Anita M et al. (February 2023). "Sex differences in skeletal muscle-aging trajectory: same processes, but with a different ranking". GeroScience 45 (4): 2367–2386. doi:10.1007/s11357-023-00750-4. PMID 36820956. 
  15. ↑ "Mammalian Mitochondria and Aging: An Update". Cell Metabolism 25 (1): 57–71. January 2017. doi:10.1016/j.cmet.2016.09.017. PMID 28094012. 
  16. ↑ "Stochastic survival of the densest and mitochondrial DNA clonal expansion in aging". Proceedings of the National Academy of Sciences of the United States of America 119 (49): e2122073119. December 2022. doi:10.1073/pnas.2122073119. PMID 36442091. Bibcode: 2022PNAS..11922073I. 
  17. ↑ "Coordination of mitochondrial and lysosomal homeostasis mitigates inflammation and muscle atrophy during aging". Aging Cell 21 (4): e13583. April 2022. doi:10.1111/acel.13583. PMID 35263007. 
  18. ↑ Naruse, Masatoshi; Trappe, Scott; Trappe, Todd (March 2023). "Human skeletal muscle-specific atrophy with aging: a comprehensive review". Journal of Applied Physiology 134 (4): 900-914. doi:10.1152/japplphysiol.00768.2022. PMID 36825643. 
  19. ↑ De Jong, Jelle; Caspers, Martien; Worms, Nicole (January 2024). "Translatability of mouse muscle-aging for humans: the role of sex". GeroScience. doi:10.1007/s11357-024-01082-7. 
  20. ↑ 20.0 20.1 "Welcome to the ICD-10 code for sarcopenia". Journal of Cachexia, Sarcopenia and Muscle 7 (5): 512–514. December 2016. doi:10.1002/jcsm.12147. PMID 27891296. 
  21. ↑ 21.0 21.1 21.2 21.3 "Skeletal Muscle Regulates Metabolism via Interorgan Crosstalk: Roles in Health and Disease". Journal of the American Medical Directors Association 17 (9): 789–796. September 2016. doi:10.1016/j.jamda.2016.04.019. PMID 27324808. 
  22. ↑ "Sarcopenia". BMJ 341 (aug10 2): c4097. August 2010. doi:10.1136/bmj.c4097. PMID 20699307. 
  23. ↑ "SARC-F: a symptom score to predict persons with sarcopenia at risk for poor functional outcomes". Journal of Cachexia, Sarcopenia and Muscle 7 (1): 28–36. March 2016. doi:10.1002/jcsm.12048. PMID 27066316. 
  24. ↑ "Sarcopenia the new geriatric giant: time to translate research findings into clinical practice". Age and Ageing 43 (6): 736–737. November 2014. doi:10.1093/ageing/afu118. PMID 25227204. 
  25. ↑ "Frailty in the elderly: the physical dimension". Europa Medicophysica 43 (3): 407–415. September 2007. PMID 17117147. http://www.minervamedica.it/index2.t?show=R33Y2007N03A0407. 
  26. ↑ "Exercise, aging, and muscle protein metabolism". The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences 58 (10): M918–M922. October 2003. doi:10.1093/gerona/58.10.m918. PMID 14570859. 
  27. ↑ "Progressive resistance strength training for improving physical function in older adults". The Cochrane Database of Systematic Reviews 2009 (3): CD002759. July 2009. doi:10.1002/14651858.cd002759.pub2. PMID 19588334. 
  28. ↑  This article incorporates text available under the CC BY 4.0 license. Anatomy & Physiology. Houston: OpenStax CNX. June 8, 2023. 10.6 Exercise and muscle performance. ISBN 978-1-947172-04-3. 
  29. ↑ 29.0 29.1 29.2 "Nutritional supplements in support of resistance exercise to counter age-related sarcopenia". Advances in Nutrition 6 (4): 452–460. July 2015. doi:10.3945/an.115.008367. PMID 26178029. 
  30. ↑ 30.0 30.1 30.2 30.3 "Sarcopenia and age-related endocrine function". International Journal of Endocrinology 2012: 127362. 28 May 2012. doi:10.1155/2012/127362. PMID 22690213. 
  31. ↑ 31.0 31.1 "Comprehensive approach to sarcopenia treatment". Current Clinical Pharmacology 9 (2): 171–180. May 2014. doi:10.2174/1574884708666131111192845. PMID 24219006. 
  32. ↑ "Increased risk of non-fatal myocardial infarction following testosterone therapy prescription in men". PLOS ONE 9 (1): e85805. 29 January 2014. doi:10.1371/journal.pone.0085805. PMID 24489673. Bibcode: 2014PLoSO...985805F. 
  33. ↑ "Association of testosterone therapy with mortality, myocardial infarction, and stroke in men with low testosterone levels". JAMA 310 (17): 1829–1836. November 2013. doi:10.1001/jama.2013.280386. PMID 24193080. 
  34. ↑ "Adverse events associated with testosterone administration". The New England Journal of Medicine 363 (2): 109–122. July 2010. doi:10.1056/NEJMoa1000485. PMID 20592293. 
  35. ↑ "Does nutrition play a role in the prevention and management of sarcopenia?". Clinical Nutrition 37 (4): 1121–1132. August 2018. doi:10.1016/j.clnu.2017.08.016. PMID 28927897. 
  36. ↑ "Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group". Journal of the American Medical Directors Association 14 (8): 542–559. August 2013. doi:10.1016/j.jamda.2013.05.021. PMID 23867520. 
  37. ↑ "Protein intake and exercise for optimal muscle function with aging: recommendations from the ESPEN Expert Group". Clinical Nutrition 33 (6): 929–936. December 2014. doi:10.1016/j.clnu.2014.04.007. PMID 24814383. 
  38. ↑ "An Update on Protein, Leucine, Omega-3 Fatty Acids, and Vitamin D in the Prevention and Treatment of Sarcopenia and Functional Decline". Nutrients 10 (8): 1099. August 2018. doi:10.3390/nu10081099. PMID 30115829. 
  39. ↑ "Amino acids and muscle loss with aging". The Journal of Nutrition 136 (1 Suppl): 277S–280S. January 2006. doi:10.1093/jn/136.1.277S. PMID 16365098. 
  40. ↑ "Muscle wasting and aging: Experimental models, fatty infiltrations, and prevention". Molecular Aspects of Medicine 50: 56–87. August 2016. doi:10.1016/j.mam.2016.04.006. PMID 27106402. https://hal.archives-ouvertes.fr/hal-01837630/file/2016_Brioche_MAM_1.pdf. 
  41. ↑ 41.0 41.1 "Effect of beta-hydroxy-beta-methylbutyrate supplementation on muscle loss in older adults: a systematic review and meta-analysis". Archives of Gerontology and Geriatrics 61 (2): 168–175. September 2015. doi:10.1016/j.archger.2015.06.020. PMID 26169182. 
  42. ↑ "Beta-hydroxy-beta-methylbutyrate supplementation and skeletal muscle in healthy and muscle-wasting conditions". Journal of Cachexia, Sarcopenia and Muscle 8 (4): 529–541. August 2017. doi:10.1002/jcsm.12208. PMID 28493406. 
  43. ↑ Xia, Lin; Zhao, Rui; Wan, Qianyi; Wu, Yutao; Zhou, Yong; Wang, Yong; Cui, Yaping; Shen, Xiaoding et al. (13 September 2020). "Sarcopenia and adverse health-related outcomes: An umbrella review of meta-analyses of observational studies". Cancer Medicine 9 (21): 7964–7978. doi:10.1002/cam4.3428. ISSN 2045-7634. PMID 32924316. 
  44. ↑ Rodrigues, Filipe; Domingos, Christophe; Monteiro, Diogo; Morouço, Pedro (13 January 2022). "A Review on Aging, Sarcopenia, Falls, and Resistance Training in Community-Dwelling Older Adults". International Journal of Environmental Research and Public Health 19 (2): 874. doi:10.3390/ijerph19020874. ISSN 1661-7827. PMID 35055695. 
  45. ↑ "New horizons in the pathogenesis, diagnosis and management of sarcopenia". Age and Ageing 42 (2): 145–150. March 2013. doi:10.1093/ageing/afs191. PMID 23315797. 
  46. ↑ Rolland, Yves; Dray, Cedric; Vellas, Bruno; Barreto, Philipe De Souto (1 December 2023). "Current and investigational medications for the treatment of sarcopenia". Metabolism 149: 155597. doi:10.1016/j.metabol.2023.155597. ISSN 0026-0495. PMID 37348598. https://www.sciencedirect.com/science/article/pii/S0026049523002019. 
  47. ↑ "Selective androgen receptor modulators (SARMs) as pharmacological treatment for muscle wasting in ongoing clinical trials". Expert Opinion on Investigational Drugs 29 (8): 881–891. August 2020. doi:10.1080/13543784.2020.1777275. PMID 32476495. 
  48. ↑ "Selective androgen receptor modulators: the future of androgen therapy?". Translational Andrology and Urology 9 (Suppl 2): S135–S148. March 2020. doi:10.21037/tau.2019.11.02. PMID 32257854. 

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