Sarcopenia in Adults with Intellectual Disability: A Scoping Review Protocol to map and describe the existing research.

Introduction

Sarcopenia is defined as an age-associated progressive and generalised loss of skeletal muscle mass and strength (Cruz-Jentoft et al., 2019). First described by Rosenberg in 1989 using the Greek words ‘sarx’ and ‘penia’ to denote ‘poverty of flesh’ (Rosenberg, 1997), sarcopenia has since 2016, become recognised as a disease in the World Health Organisation (WHO)’s International Statistical Classification of Diseases and Related Health Problems (ICD) (M62.84) (WHO, 2004). This reflects an important step taken to recognise sarcopenia in clinical practice. Sarcopenia is common in older adults in the general population and a systematic review conducted by Petermann-Rocha et al. (2022) estimated its prevalence to be approximately 10–27% in adults aged 60 years and older, with its prevalence rising with increasing age (Meng et al., 2024; Papadopoulou, 2020). There is increasing recognition that the presence of sarcopenia is associated with adverse health consequences including mobility difficulties, falls, frailty, functional decline and hospitalisation, resulting in higher healthcare costs, mortality and public health burden (Beaudart et al., 2017; Lim et al., 2022). As a result, major efforts have been made by academics and clinicians to review practices for screening, diagnosis and management in the general older population, with the objective of developing intervention and treatment options that can potentially prevent and reverse sarcopenia (Marcos-Pardo et al., 2020; Marzetti et al., 2017).

The phenomenon of increasing longevity with its related challenges are similarly encountered in people with intellectual disability, who are living longer, leading to a rapidly increasing proportion of adults ageing with intellectual disability (Dolan et al., 2021; McCallion & McCarron, 2004). The increased longevity can be particularly demanding in this group as the rise in age related disabilities compound pre-existing lifelong disabilities, leading to further challenges for this already vulnerable population and their families (Brennan et al., 2020; Ryan et al., 2014). Moreover, with the added phenomenon of premature ageing in people with intellectual disability (Garcia-Dominguez et al., 2020; Gensous et al., 2020), it is especially important to assess for potential health issues early, as leaving these untreated could lead to worsening function and morbidity for longer periods (Dolan et al., 2021).

With this in mind, researchers in the field of intellectual disability have in recent years also started exploring sarcopenia in the population of older adults with intellectual disability. Carmeli et al. (2012) reported the findings of a non-randomised, controlled and double-blinded, cross-sectional study, which set out to determine the association between sarcopenia, presarcopenia and physical ability in persons with intellectual disability. Overall, 44 adults living in a residential center in Vancouver with the average age of 59.7 +/- 7.7 years participated in this study, with sex and aged matched individuals without intellectual disability serving as the control group. The functional ability, muscle strength and muscle mass of the participants were assessed using two physical tests (sit-to-stand and stair climb) and with the Katz ADL questionnaire (Katz & Akpon, 1976). The results demonstrated a higher prevalence of sarcopenia in the group with intellectual disability compared to the control group, and this was strongly related to poorer functional and physical ability (p< 0.001). Though limited by the small number of participants, this suggests not only that the prevalence of sarcopenia is higher in adults with intellectual disability compared to the general population, but also that sarcopenia is strongly associated with functional impairments.

The negative impact of sarcopenia in older adults with intellectual disability was also reported by Bastiaanse et al. (2012), as part of the HA-ID study conducted in Netherlands. In this study, the prevalence and associations of sarcopenia was examined in 884 participants above the age of 50 years. The criteria of the European Working Group on Sarcopenia in Older People (EWGSOP) (Cruz-Jentoft et al., 2019) was used in this study to define sarcopenia. Analysis of the results showed a strong relationship between sarcopenia and mobility impairment, with participants who were wheelchair dependant being 34 times more likely to have sarcopenia (OR 34.23). This finding is especially important as the presence of mobility difficulties has been shown by several studies to be a predictor of mortality in people with intellectual disability (Hosking et al., 2016; Tyrer et al., 2007). The strong association of sarcopenia with mobility impairment suggests that the presence of sarcopenia could also have implications on mortality. Furthermore, as part of the HA-ID study, a review of all-cause mortality measured over a 5-year period showed that the presence of sarcopenia in the participants is an independent risk factor for early mortality for older adults with intellectual disability (Valentin et al., 2023). Though these associations of sarcopenia are yet to be extensively studied, these findings highlight the potential importance and serious implications of sarcopenia in people with intellectual disability.

In view of the considerable impact sarcopenia has on function and health outcomes in the general population, there has been urgency in recent years to develop effective screening and diagnostic tools that can be utilised for early detection and intervention (Ackermans et al., 2022; Ishii et al., 2014). A number of screening tools are currently in use, including grip strength, gait speed and the SARC-F, a 5-item questionnaire that looks at strength, assistance with walking, rising from a chair, climbing stairs and falls (Malmstrom & Morley, 2013). These screening tools are not only accessible but also easily integrated into routine clinical practice, allowing for early identification. Once identified, the next step involves utilising objective assessment tools to diagnose sarcopenia, which will require the clinician to assess individuals based on specific criteria; low muscle strength, low muscle quantity or quality and, low physical performance. All of these can be measured using a variety of assessment tools and scales. These include measuring the calf circumference, assessing grip strength, analysing gait speed and carrying out imaging studies such as computed tomography (CT), magnetic resonance imaging (MRI), dual energy X-ray absorptiometry (DXA) and bioelectric impedance (BIA) (Cruz-Jentoft et al., 2019).

Several international work groups, including the Asian Working Group for Sarcopenia (AWGS) and the International Clinical Practice Guidelines for Sarcopenia (ICFSR) have proposed diagnostic algorithms and management pathways for sarcopenia to guide clinical practice (Chen et al., 2020; Dent et al., 2018). However, these guidelines may not be suitable for adults with intellectual disability due to the different background health status, potential difficulties in utilising certain screening and diagnostic tools, the lack of validation of these assessments in this population and finally, unique challenges in implementing intervention plans in a population with intrinsic cognitive and communication difficulties.

Extensive research in the general population has addressed not only the diagnosis of sarcopenia but also its prevention and treatment (Cho et al., 2022; Landi et al., 2018). Key management strategies include promotion of physical activity, structured exercise programmes and targeted dietary interventions (Beaudart et al., 2017; Morley, 2016). These approaches have demonstrated significant potential in mitigating sarcopenia’s progression and improving overall health outcomes (Bruyere et al., 2022; Denison et al., 2015). In his review, Beaudart et al. (2017) reports a clear positive effect on muscle mass and function in healthy participants aged 60 years when physical exercise programmes are instituted, with the biggest effect seen in physical performance. Studies examining physical activity and exercises carried out in adults with intellectual disability have also shown improvement in muscle endurance, flexibility and strength, which suggests that similar interventions to increase muscle strength could also prove effective in adults with intellectual disability for the prevention of sarcopenia (Bouzas et al., 2019). Additionally, dietary interventions to treat sarcopenia have been examined in several studies, with a diet sufficient in protein, vitamin D and antioxidants found to be beneficial in reducing sarcopenia in the general population (Robinson et al., 2018; Yanai, 2015). Given that nutrition is recognised to be an aspect commonly overlooked in adults with intellectual disability, often resulting in malnutrition or obesity, this is a potentially important area of intervention as well (Heller et al., 2011; Humphries et al., 2009). Koritsas & Iacono (2016) explored the physical activity and nutrition of 51 community dwelling people with intellectual disability and found that only 37.5% of the participants had a healthy range for their body mass index (BMI), with 17.6% in the high-risk category for malnutrition. In addition, 60.3% of the participants did not meet national physical activity guidelines. These findings suggest that people with intellectual disability are at risk of developing conditions associated with poor nutrition and inactivity, which includes sarcopenia.

Considering the potential profound negative impact on function and quality of life in a group already contending with lifelong disabilities, it is imperative that more is known about sarcopenia in people with intellectual disability. Their baseline health status, combined with a general lack of physical activity and poorer nutrition, significantly increases their risk of developing sarcopenia. These factors are critical considerations in both the development of the condition and the formulation of effective treatment plans. However, despite this, there is a paucity of knowledge and evidence regarding sarcopenia in people with intellectual disability amongst academics and clinicians. It is therefore of critical importance to prioritise the screening, diagnosis and treatment of sarcopenia in persons with intellectual disability, and conduct further studies to understand the condition in this vulnerable population. Being a potentially preventable and treatable condition, understanding sarcopenia better and developing evidence informed intervention plans could lead not only to overall improvement in quality of life for people with intellectual disability, but also reduced healthcare burden and cost. This scoping review therefore aims to map and describe the existing research on sarcopenia in adults with intellectual disability, in order to inform further research, policy and clinical practice.

Methods

Scoping reviews are defined as ‘’a type of evidence synthesis that aims to systematically identify and map the breadth of evidence available on a particular topic, field, concept, or issue, often irrespective of source (ie. Primary research, reviews, non-empirical evidence) within or across particular contexts.’’ (Munn et al., 2022). Through exploring the breadth of research for a topic or concept, scoping reviews summarise existing research and identify not only what is already known but also what the existing gaps may be. This scoping review will be conducted in accordance with the guidelines from the Joanna Briggs Institute (JBI) (Peters et al., 2015) and based on the Arksey and O’Malley framework (Arksey & O’Malley, 2005).

The framework of Arksey and O’Malley consists of five stages:

Each of these stages will be presented below.

Discussion

The findings of this scoping review will provide an overview of what is known in existing literature about sarcopenia in adults with intellectual disability. By identifying key gaps in knowledge, this review will pinpoint areas that require further investigation among those with intellectual disability. Importantly, it will highlight the potential clinical implications of these knowledge gaps, underscoring the need for targeted research to address them. This will not only strengthen the development of more accurate screening, diagnosis, and management strategies for sarcopenia in this population but also justify the need for further studies to improve health outcomes and promote overall wellbeing. In this way, the scoping review will provide a critical rationale for advancing research efforts in this underexplored area. This will form a base from which further research can be conducted to inform the screening, diagnosis and management of sarcopenia in this population group to promote positive health and wellbeing.