14.3: Neurocognitive Disorders - Etiology

Learning Objectives

• Define degenerative.
• Describe the symptoms and causes of Alzheimer’s disease.
• Describe the symptoms and causes of traumatic brain injury (TBI).
• Describe the symptoms and causes of vascular disorders.
• Describe the symptoms and causes of substance/medication-induced major or mild NCD .
• Describe the symptoms and causes of dementia with Lewy bodies.
• Describe the symptoms and causes of frontotemporal NCD.
• Describe the symptoms and causes of Parkinson’s disease.
• Describe the symptoms and causes of Huntington’s disease.
• Describe the symptoms and causes of HIV infection.

Neurocognitive disorders occur due to a wide variety of medical conditions or injury to the brain. Therefore, this section will focus on a brief description of the nine different etiologies of neurocognitive disorders per the DSM-5-TR (APA, 2022). As you will see, most of these neurocognitive disorders are both degenerative, meaning the symptoms and cognitive deficits become worse over time, as well as related to a medical condition or disease.

Per the DSM-5-TR (APA, 2022), an individual will meet diagnostic criteria for either mild or major neurocognitive disorder as listed above. In order to specify the type of neurocognitive disorder, additional diagnostic criteria specific to one of the following subtypes must be met.

Alzheimer’s Disease

Alzheimer’s disease is the most prevalent neurodegenerative disorder. While the primary symptom of Alzheimer’s disease is the gradual progression of impairment in cognition, it is also important to identify concrete evidence of cognitive decline. This can be done in one of two ways: via genetic testing of the individual or a documented family history of the disease, or, through clear evidence of cognitive decline over time by repeated standardized neuropsychological evaluations (APA, 2022). It is crucial to identify these markers in making the diagnosis of Alzheimer’s disease as some individuals present with memory impairment but eventually show a reversal of symptoms; this is not the case for individuals with Alzheimer’s disease.

14.3.1.1. Causes of Alzheimer’s disease. Autopsies of individuals diagnosed with Alzheimer’s disease identify two abnormal brain structures— beta-amyloid plaques and neurofibrillary tangles— both of which are responsible for neuron death, inflammation, and loss of cellular connections (Lazarov, Mattson, Peterson, Pimplika, & van Praag, 2010). It is believed that beta-amyloid plaques, large bundles of plaque that develop between neurons, appear before the development of dementia symptoms. As these plaque bundles increase in size and number, cognitive symptoms and impaired daily functioning become evident to close family members. Neurofibrillary tangles are believed to appear after the onset of dementia symptoms and are found inside of cells, affecting the protein that helps transport nutrients in healthy cells. Both beta-amyloid plaques and neurofibrillary tangles impact the health of neurons within the hippocampus, amygdala, and the cerebral cortex, areas associated with memory and cognition (Spires-Jones & Hyman, 2014).

Researchers have identified additional genetic and environmental influences in the development of Alzheimer’s disorder. Genetically, the apolipoprotein E (ApoE) gene that helps to eliminate beta-amyloid by-products from the brain, has been implicated in the development of Alzheimer’s disorder. One of the three variants of this gene, the e4 allele, appears to reduce the production of ApoE, thus increasing the number of beta-amyloid plaques within the brain. However, not all individuals with the e4 allele develop Alzheimer’s disease; therefore, this explanation may better explain a vulnerability to Alzheimer’s disease as opposed to the cause of the disease.

Various brain regions have also been implicated in the development of Alzheimer’s disease. More specifically, neurons shrinking or dying within the hypothalamus, thalamus, and the locus ceruleus have been linked to declining cognition (Selkoe, 2011, 1992). Acetylcholine-secreting neurons within the basal forebrain also appear to shrink or die, contributing to Alzheimer’s disease symptoms (Hsu et al., 2015).

Environmental toxins such as high levels of zinc and lead may also contribute to the development of Alzheimer’s disease. More precisely, zinc has been linked to the clumping of beta-amyloid proteins throughout the brain. Although lead has largely been phased out of environmental toxins due to negative health consequences, current elderly individuals were exposed to these toxic levels of lead in gasoline and paint as young children. There is some speculation that lead and other pollutants may impact cognitive functioning in older adults (Richardson et al., 2014).

14.3.1.2. Onset of Alzheimer’s disease. Alzheimer’s disease is defined by the onset of symptoms. Early-onset Alzheimer’s disease occurs before the age of 65. While only a small percentage of individuals experience early onset of the disease, those that do experience early disease progression appear to have a more genetically influenced condition and a higher rate of family members with the disease.

Late-onset Alzheimer’s disease occurs after the age of 65 and has less of a familial influence. This onset appears to occur due to a combination of biological, environmental, and lifestyle factors (Chin-Chan, Navarro-Yepes, & Quintanilla-Vega, 2015). Nearly 30% of individuals within this class of diagnosis have the ApoE gene that fails to eliminate the beta-amyloid proteins from various brain structures. It is believed that the combination of the presence of this gene along with environmental toxins and lifestyle choices (i.e., more stress) impact the development of Alzheimer’s disease.

Traumatic Brain Injury (TBI)

TBIs occur when an individual experiences significant trauma or damage to the head. Neurocognitive disorder due to TBI is diagnosed when persistent cognitive impairment is observed immediately following the head injury, along with one or more of the following symptoms: loss of consciousness, posttraumatic amnesia, disorientation and confusion, or neurological impairment (APA, 2022).

The presentation of symptoms varies among individuals and depends largely on the location of the injury and the intensity of the trauma. Furthermore, the effects of a TBI can be temporary or permanent. Symptoms generally range from headaches, disorientation, confusion, irritability, fatigue, poor concentration, and emotional and behavioral changes. More severe injuries can result in more significant neurological symptoms such as seizures, paralysis, and visual disturbances.

Major or mild NCD due to TBI may be comorbid with specified or unspecified depressive, anxiety, or personality disorders and PTSD. Rates of suicidal ideation are as high as 10% with rates of suicide attempt hovering around 0.8% to 1.7% (APA, 2022).

The most common type of TBI is a concussion. A concussion occurs when there is a significant blow to the head, followed by changes in brain functioning. It often causes immediate disorientation or loss of consciousness, along with headaches, dizziness, nausea, and sensitivity to light (Alla, Sullivan, & McCrory, 2012). While symptoms of a concussion are usually temporary, there can be more permanent damage due to repeated concussions, particularly if they are close in time. The media has brought considerable attention to this with the recent discussions of chronic traumatic encephalopathy (CTE) which is a progressive, degenerative condition due to repeated head trauma. CTEs are most commonly seen in athletes (i.e., football players) and military personnel (Baugh et al., 2012). In addition to the neurological symptoms, psychological symptoms such as depression and poor impulse control have been observed in individuals with CTE. These individuals also appear to be at greater risk for the development of dementia (McKee et al., 2013).

Vascular Disorders

Neurocognitive disorders due to vascular disorders can occur from a one-time event such as a stroke or ongoing subtle disruptions of blood flow within the brain (APA, 2022). The occurrence of these vascular disorders general begins with atherosclerosis, or the clogging of arteries due to a build-up of plaque. The plaque builds up over time, eventually causing the artery to narrow, thus reducing the amount of blood able to pass through to other parts of the body. When these arteries within the brain become entirely obstructed, a stroke occurs. The lack of blood flow during a stroke results in the death of neurons and loss of brain function. There are two types of strokes—a hemorrhagic stroke that occurs when a blood vessel bursts within the brain and an ischemic stroke, which is when a blood clot blocks the blood flow in an artery within the brain (American Stroke Association, 2017).

While strokes can occur at any age, the majority of strokes occur after age 65 (Hall, Levant, & DeFrances, 2012). A wide range of cognitive, behavioral, and emotional changes occur following a stroke. Symptoms are generally dependent on the location of the stroke within the brain as well as the extensiveness of damage to those brain regions (Poels et al., 2012). For example, strokes that occur on the left side of the brain tend to cause problems with speech and language, as well as physical movement on the right side of the body; whereas strokes that occur on the right side of the brain tend to cause problems with impulsivity and impaired judgement, short-term memory loss, and physical movement on the left side of the body (Hedna et al., 2013).

After Alzheimer’s disease, vascular disease is the second most common cause of NCD and population prevalence estimates are 0.98% for those between the ages of 71-79 years, 4.09% for individuals aged 80-89 years, and 6.19% for those aged 90 years and up. Within three months of a stroke, 20%-30% of people are diagnosed with dementia. Finally, stroke is more common in men up to age 65 and after that, it shifts to women. Vascular disease is frequently comorbid with major or mild NCD due to Alzheimer’s disease and depression.

Substance/Medication-Induced Major or Mild NCD

Significant cognitive changes occur due to repetitive drug and alcohol abuse. Delirium can be observed in individuals with extreme substance intoxication, withdrawal, or even when multiple substances have been used within a close period (APA, 2022). While delirium symptoms are often transient during these states, mild neurocognitive impairment due to heavy substance abuse may remain until a significant period of abstinence is observed (Stavro, Pelletier, & Potvin, 2013).

Dementia with Lewy Bodies

Symptoms associated with neurocognitive disorder due to Lewy bodies include significant fluctuations in attention and alertness; recurrent visual hallucinations; impaired mobility; and sleep disturbances such as rapid eye movement sleep behavior disorder (APA, 2022). While the trajectory of the illness develops more rapidly than Alzheimer’s disease, the survival period is similar in that most individuals do not survive longer than eight years post-diagnosis (Lewy Body Dementia Association, 2017).

Lewy bodies are irregular brain cells that result from the buildup of abnormal proteins in the nuclei of neurons. These brain cells deplete the cortex of acetylcholine, which causes the behavioral and cognitive symptoms observed in both dementia with Lewy bodies and Parkinson’s disease. The motor symptoms seen in both these disorders occur from the depletion of dopamine by the Lewy body nerve cells that accumulate in the brain stem.

Major or Mild Frontotemporal NCD

Frontotemporal NCD causes “progressive development of behavioral and personality change and/or language impairment” (APA, 2022, pg. 696). For the behavioral variant, individuals display at least three of the following: behavioral disinhibition, apathy or inertia, loss of sympathy or empathy, preservative or compulsive behavior, or hyperorality and dietary changes. For the language variant, they show prominent decline in language ability (i.e., speech production, word finding, object naming, grammar, or word comprehension). There is relative sparing of learning and memory and perceptual-motor functioning. Individuals with frontotemporal NCD commonly present in their 50s though the age of onset has a range of age 20 to 80 years. The median survival is 6-11 years after symptom onset and 3-4 years after diagnosis (APA, 2022).

Parkinson’s Disease

The awareness of Parkinson’s disease has increased in recent years due in large part to Michael J. Fox’s early diagnosis in 1991. It affects approximately 630,000 individuals (Kowal, Dall, Chakrabarti, Storm, & Jain, 2013). While many are aware of the tremors of hands, arms, legs, and face, the other three main symptoms of Parkinson’s disease are rigidity of the limbs and trunk; slowness in initiating movement; and drooping posture or impaired balance and coordination (National Institute of Neurological Disorders and Stroke, 2017). These motor symptoms are generally present at least one year prior to the beginning of cognitive decline, although severity and progression of symptoms vary significantly from person to person.

Onset of Parkinson’s disease is typically from age 50 to 89 years. Mild NCD develops early in the course of Parkinson’s disease while Major NCD does not occur until individuals are much older. The prevalence of Parkinson’s disease in the U.S. increases with age and is more common in men than women. The disease is comorbid with Alzheimer’s disease and cerebrovascular disease. Depression, psychosis, REM sleep behavior disorder, apathy, and motor symptoms can make functional impairment worse (APA, 2022).

Huntington’s Disease

Huntington’s disease is a rare genetic disorder that involves involuntary movement, progressive dementia, and emotional instability. Due to the degenerative nature of the disorder, there is a shortened life-expectancy as death typically occurs 15-20 years post-onset of symptoms (Clabough, 2013). Although symptoms can present at any time, the average age of symptom presentation is during middle adulthood (between ages 35 and 45 years; APA, 2022). Symptoms generally begin with neurocognitive decline, particularly in executive function, along with changes in mood and personality. As symptoms progress, more physical symptoms present, such as facial grimaces, difficulty speaking, and repetitive movements. Because there is no treatment for Huntington’s disease, the severity of the cognitive and physical impairments ultimately leads to complete dependency and the need for full-time care. Suicide is among the leading causes of death in Huntington’s disease (APA, 2022).

HIV Infection

Not many people are aware that cognitive impairment is sometimes the first symptom of untreated HIV. While symptoms vary among individuals, slower mental processing, impaired executive function, problems with more demanding attentional tasks, and difficulty learning new information are among the most common early signs (APA, 2022). When HIV becomes active in the brain, significant alterations of mental processes occur, thus leading to a diagnosis of neurocognitive disorder due to HIV infection. Significant impairment can also occur due to HIV-infection related inflammation throughout the central nervous system.

Fortunately, antiretroviral therapies used in treating HIV have been effective in reducing and preventing the onset of severe cognitive impairments; however, HIV-related brain changes still occur in nearly half of all patients on antiretroviral medication. There is hope that once antiretroviral therapies can cross the blood-brain barrier in the central nervous system, there will be a significant improvement in the prevalence of HIV-related neurocognitive disorder (Vassallo et al., 2014).

Key Takeaways

You should have learned the following in this section:

• Most neurocognitive disorders are degenerative meaning they become worse over time.
• Alzheimer’s disease is characterized by the gradual progression of impairment in cognition as well as the presence of beta-amyloid plaques and neurofibrillary tangles.
• TBIs occur when an individual experiences significant trauma or damage to the head with the most common type being a concussion.
• Vascular disorders generally begin with atherosclerosis which leads to a stroke.
• Significant cognitive changes occur due to repetitive drug and alcohol abuse such as delirium.
• Dementia with Lewy bodies is characterized by significant fluctuations in attention and alertness; recurrent visual hallucinations; impaired mobility; and sleep disturbance.
• Frontotemporal NCD causes progressive declines in language or behavior due to the degeneration in the frontal and temporal lobes of the brain.
• Parkinson’s disease is characterized by tremors of hands, arms, legs, or face; rigidity of the limbs and trunk; slowness in initiating movement; and drooping posture or impaired balance and coordination.
• Huntington’s disease involves involuntary movement, progressive dementia, and emotional instability.
• HIV infection begins with slower mental processing, impaired executive function, problems with more demanding attentional tasks, and difficulty learning new information.

Review Questions

1. Define degenerative. What disorders discussed in this module are considered degenerative?
2. Identify the biological causes of Alzheimer’s disease.
3. What is a TBI?
4. How do vascular disorders occur?
5. What are Lewy bodies? How does dementia with Lewy bodies differ from Alzheimer’s disease?
6. What are the main symptoms of Parkinson’s disease? Huntington’s disease?