The Role of Neuroimaging in Fall Prevention in Healthy Adults at Risk of Alzheimer's Disease

Introduction

Falls are important clinical, socioeconomic, and public health problem in the older adult population. Falls have been linked to premature institutionalization, injury, functional reduction, decrease in autonomy, and injury-related mortality (Tinetti & Williams, 1997). The World Health Organization (WHO) (2019a) identified fall as the second major cause of accidental or unintentional injury deaths worldwide. Annually, it is estimated that 646, 000 individuals die from falls, with over 80% occurring in low- and middle-income countries (WHO, 2019a). The greatest number of fatal falls have been noted to occur among adults older than 65 years of age (WHO, 2019a). Globally, adults above the age of 70 years, particularly females, demonstrate significantly increased fall-related death rates compared to younger people (WHO, 2019b).

Previous epidemiological studies have identified a number of potential intrinsic and extrinsic risk factors for falls in community‐dwelling elderly people (Deandrea et al., 2010). Intrinsic risk factors for fall include advanced age, history of falls, gait and balance problems, muscle weakness, poor vision, sleep disturbances, and chronic diseases such as arthritis, stroke, diabetes, dementia, Parkinson's, and incontinence (Deandrea et al., 2010; Hopewell et al., 2018; Rajagopalan, Litvan, & Jung, 2017). On the other hand, extrinsic risk factors for falls include environmental factors i.e. lack of hand rails, wet, slippery or uneven surfaces, poor lighting, use of walking aids, poor footwear, and clutter (Todd & Skelton, 2004; Rajagopalan et al., 2017). It is estimated that close to 15% of falls occur as a result of major external event that would result in falls in most people (Hopewell et al., 2018). Even though similar percentage of falls occur from a single identifiable event i.e. syncope (Hopewell et al., 2018), most occur as a result of multiple interacting factors (e.g. balance problems, poor vision, and slips on an uneven surface) (Campbell & Robertson, 2006). Generally, the risk of fall tends to increase with more risk factors (Hopewell et al., 2018).

Cognitively impaired people have been reported to experience falls up to more than two times than cognitively normal individuals, often leading to more serious consequences (Allan, Ballard, Rowan, & Kenny, 2009; Taylor, Ketels, & Delbaere, 2012). Despite that the reasons underlying the higher prevalence of falls remain unclear, neurodegenerative changes in mild cognitive impairment (MCI) and Alzheimer's disease (AD) may heighten the risk of falls due to alterations in executive functions, ability to solve problems or make decisions, and ability to perform simultaneous tasks (Taylor et al., 2013; Sheridan & Hausdorff, 2007). Individuals with AD dementia have been reported to have an increased risk of serious falls (Sheridan & Hausdorff, 2007). There is also evidence that gait changes and falls are associated with non-AD dementias (Verghese et al., 2002). The rate of falls is estimated to be almost three times more evident than that observed among non-demented elderly (Weller & Schatzker, 2004). In a longitudinal study which compared falls in AD and normal aging, 36% of the participants with AD were noted to have had falls compared to 11% of the age matched controls (Weller & Schatzker, 2004). Higher rate of institutionalization was also reported among fallers, suggesting an interrelation between AD, falls, and loss of independence (Sheridan & Hausdorff, 2007).