With the reduction of the birth rate and the rapid growth of the elderly community, we are fast turning into an aged population. As live expectancy increases, age-related disorders increase as well, bringing with them great economic challenges for governments and society in general. Important efforts are being made all around the world in the search for methods of detecting and treating these disorders in effective and inexpensive ways.
From the wide range of age-related disorders, dementing illnesses are highly common, being Alzheimer’s disease the most prevalent condition with 65% of all cases (Alzheimer Society of Canada, 2014). The prevalence of AD increases with age; 10% of people age 65 and older are affected by the disease, and this number increases to almost a third of the population over 85 years old (Alzheimer’s Association, 2018a). Over 80% of AD cases are from people aged 75 and older.
Alzheimer’s disease is a degenerative brain disease whose main causes remain unknown. Although there is a genetic component associated to AD, it is estimated that only 1% of the
cases are caused by a genetic mutation (Bekris, Yu, Bird, & Tsuang, 2010). It is believed that AD is caused by a combination of multiple factors, rather than by a unique cause. The main risk factors of AD are older age, having a first-degree relative diagnosed with AD, and having inherited the APOE-e4 risk gene. However, several modifiable risk factors also play a crucial role in the development of the disease (Baumgart et al., 2015), such as smoking, obesity, hypertension, and high cholesterol levels.
The American Alzheimer’s Association (2018, 2011) identifies early detection of Alzheimer’s disease as one of the biggest challenges faced by physicians when dealing with dementing illnesses. It is highly common to diagnose a person suffering from Alzheimer’s dementia several years after the disease has initiate, which means that by the time a proper diagnosis has been made, the condition has already made severe damage to the patient.
The revised AD diagnostic guidelines (Sperling et al., 2011) establish the progression of signs and symptoms that occur along the disease continuum. This continuum starts with brain changes that may begin 20 years prior to the appearance of any symptoms (Villemagne et al., 2013), yielding a potential for early diagnosis (Alzheimer’s Association, 2018a).
The disease progression starts with the slow accumulation of the protein fragment beta- amyloid outside neurons, and the accumulation of a mutation of the protein tau inside neurons. Beta-amyloid interferes with neurons synapses, while tau tangles impede nutrients to reach inside neurons (Alzheimer’s Association, 2018a).
At the first stage, the brain is able to compensate for these changes, allowing the individual to function normally for several years. In individuals with high education or that regularly perform cognitively demanding and mentally stimulating activities, this compensation mechanism, also known as the cognitive reserve, allows them to function with normality for a longer time (Almeida et al., 2015). However, through time, the amount of damage reaches a point in which a slow decline in cognitive functions is evident in the patient.
The first stage of symptomatic AD is known as Mild Cognitive Impairment (MCI). At this stage, patients often refer to symptoms like loss of memory and concentration. However, their symptoms are not severe enough to interfere in the patient’s daily life activities. While MCI is a part of the normal progression of AD, it is important to note that a diagnosis of MCI impairment is not necessary an AD sentence, since not all MCI cases are caused by AD (Smith & Bondi, 2013). Some MCI symptoms may be derived from depression, obstructive sleep apnea, vitamin B12 deficiency or even from certain medications. Some MCI individuals will
remain in that state indefinitely, while others might even revert to a normal cognition. An estimated 32% of individuals with an MCI diagnosis will progress to AD in the next 5 years (Ward, Tardiff, Dye, & Arrighi, 2013). The timely identification of these patients remains a major goal on AD research (Alzheimer’s Association, 2018a).
After MCI, the next stage is Alzheimer’s dementia, where the brain is no longer able to compensate for the changes. At the moderate stage of the dementia, there are noticeable memory, thinking and behavioral symptoms that are severe enough to interfere with a person’s daily life activities. Patients experiment confusion with time and place. They also may present mood changes that are caused by confusion, suspicion, depression and anxiety. Their working memory functions are severely affected, impairing their ability to retain recent information. They have difficulties following plans or instructions, and with concentration. Language functions in patients with Alzheimer’s dementia are noticeably altered, making them struggle with vocabulary and joining conversations. This stage is usually the longest (Alzheimer’s Association, 2018a).
At the final stage, patients require continuous help with basic activities of daily living, and their ability to communicate is limited. In this phase, the damage in the brain is so extensive that it interferes with the areas in charge of movement. Patients with advanced Alzheimer’s dementia eventually become bed-bound and lose control of their ability to swallow, making them vulnerable to aspiration pneumonia, which is the leading cause of death among individuals with AD (Burns, Jacoby, Luthert, & Levy, 1990).
Detecting Alzheimer’s diseases at the MCI stage may present multiple benefits for patients and the general society (Alzheimer’s Association, 2018a). Control of blood pressure, mental activity stimulation, aerobic exercise, smoking cessation and stroke prevention appear to reduce the risk of progression from MCI to dementia (Langa & Levine, 2014). An early diagnosis also gives time to individuals for planning for the future and to make important choices before their cognitive abilities fade, such as legal directives, including end-of-life care and planning. An opportune diagnosis also provides patients with the opportunity of joining clinical trials available (Dubois et al., 2016), which may allow a better and inexpensive monitoring of the patient, as well as access to new therapies. Finally, patients that have a timely diagnosis and start arrestive treatments, remain longer in their communities, which reduces stress and costs to patients and caregivers (Dubois et al., 2016).
According to (Alzheimer’s Association, 2018a), the methods and studies that are being most researched for early diagnosis of Alzheimer’s are biomarkers, brain imaging/neuroimaging (magnetic resonance imaging and computed tomography), cerebrospinal fluid proteins, and genetic risk profiling. However, most of these studies are expensive, invasive or may expose the patient to unnecessary pain or risk. It is therefore important that these tests are used as a mechanism of confirmation of diagnoses, rather as in regular medical practice.
The most usually evaluated cognitive abilities when diagnosing dementia are episodic memory, executive function, perceptual speed, verbal ability, visuospatial skill, attention and language (Taler & Phillips, 2008). From the wide variety of cognitive abilities altered in Alzheimer’s patients, language alterations are of great interest to researchers since many studies have found them even at the beginning of the disease (Schröder, Wendelstein, & Felder, 2010). There have been numerous recent studies that have focused their attention on the analysis of language production of Alzheimer’s patients as a non-invasive and economical means to detect this disease.