Some causes of cognitive decline are treatable or even reversible while others, such as Alzheimer’s disease, are progressive and irreversible. Once brain cells are damaged and lost, no matter what the cause, they cannot be repaired.
How Dementia Affects Cognition
Dementia is a syndrome, a collection or grouping of symptoms that can affect, damage, or destroy cells in the brain. Dementia is progressive, meaning it gets worse over time. Dementia can be the main cause of brain disease or it can develop as a result of accidents, tumors and cysts, concussions, cardiovascular disorders, uncontrolled diabetes, neurologic disorders such as Parkinson’s disease, alcohol and drug abuse, and a number of other disorders and diseases.
Dementia affects cognition: thinking, memory, judgment, learning, language comprehension, attitudes, beliefs, safety awareness, morals, and the ability to plan for the future are all affected to some degree. Dementia also affects motor and sensory functions such as balance, spatial awareness, vision, pain processing, and the ability to modulate (control) sensory input.
Potentially Treatable Conditions
There are many conditions that can affect cognition, causing dementia-like symptoms; some of these conditions are reversible with appropriate treatment:
- Reactions to medications or interactions between medications
- Metabolic and endocrine abnormalities
- Nutritional deficiencies
- Head injuries and subdural hematomas
- Poisoning from exposure to lead, heavy metals, or other poisonous substances
- Alcohol, prescription medications, and recreational drugs
- Brain tumors, space-occupying lesions, and hydrocephalus
- Hypoxia or anoxia (not enough oxygen)
- Autoimmune cognitive syndromes
- Sleep apnea (NINDS, 2020)
Delirium and depression can also affect cognition, are particularly prevalent, and often overlooked or misunderstood in older adults. Both conditions can be superimposed on dementia, particularly in older hospitalized patients.
Delirium characteristically has an acute onset, fluctuating course, and the presence of an underlying medical condition, medication or psychoactive substance, or medication/substance withdrawal. Patients with behavioral and psychological symptoms of dementia can also have superimposed delirium as a cause for an abrupt worsening of their usual symptoms. History is the key to differentiating behavioral and psychological symptoms from delirium: in delirium, the onset of symptoms occurs over days to 1 to 2 weeks, while in behavioral and psychological symptoms of dementia, symptoms gradually worsen over several weeks to months (Cloak and Khalili, 2020).
Patients with delirium frequently have changes in the level of consciousness, such as periods of somnolence or extended periods of wakefulness, which are typically less prominent in behavioral and psychological symptoms of dementia. Visual hallucinations may be prominent in delirium, whereas delusions are more common in patients with behavioral and psychological symptoms of dementia. It can be challenging to distinguish Lewy body dementia from delirium, since patients with Lewy body may have visual hallucinations and fluctuations in the level of consciousness, but these symptoms will have a more gradual onset than in patients with delirium (Cloak and Khalili, 2020).
Patients with suspected delirium should have a thorough medical evaluation, beginning with history and physical and followed by targeted laboratory testing and imaging based on these findings; typically, comprehensive metabolic panel, CBC, urinalysis, cardiac enzymes, chest X-ray, and toxicology screens are performed routinely, with neuroimaging, lumbar puncture, blood gases, and EEG reserved for select cases. Unlike behavioral and psychological symptoms of dementia, symptoms related to delirium will resolve, albeit sometimes gradually, once the underlying cause is corrected (Cloak and Khalili, 2020).
The most common causes of delirium are related to medication side effects, hypo or hyperglycemia (too much or too little blood sugar), fecal impactions, urinary retention, electrolyte disorders and dehydration, infection, stress, metabolic changes, an unfamiliar environment, injury, or severe pain.
Inattention is the most frequent clinical finding in a delirium episode. Other symptoms include difficulty with:
- Language and thought
- Visuospatial abilities
- Deficits in visual perception such as illusions and hallucinations (Cerejeira and Mukaetova-Ladinska, 2011)
NHS Leicester’s Hospital, England, U.K.
The prevalence of delirium increases with age, and nearly 50% of patients over the age of 70 experience episodes of delirium during hospitalization. Delirium is under-diagnosed in almost two-thirds of cases or is misdiagnosed as depression or dementia. Early diagnosis of delirium can lead to rapid improvement. However, diagnosis is often delayed, and problems remain with recognition and documentation of delirium by healthcare providers (Hope et al., 2014).
Depression is a disorder of mood involving a disturbance of emotions or feelings. The diagnosis of depression depends on the presence of two cardinal symptoms: (1) persistent and pervasive low mood, and (2) loss of interest or pleasure in usual activities. Depressive symptoms are clinically significant when they interfere with normal activities and persist for at least two weeks, in which case a diagnosis of a depressive illness or disorder may be made (Diamond, 2015).
Because of these complexities, diagnosing depression in patients with dementia can be difficult. Denial and cognitive impairment may compromise self‐report of depressive symptoms. As a person’s dementia progresses, the presentation of depression may alter, with non‐verbal behaviors such as demanding behavior and clinging being more apparent than cognitive features. Moreover, autonomic symptoms such as poor concentration and anhedonia* are features of both depression and dementia (Dudas et al., 2018).
*Anhedonia: a reduction in, or complete lack of ability, to enjoy activities the person usually finds enjoyable.
Although depression can be hard to recognize in people with dementia, there is evidence that it is common and associated with increased disability, poorer quality of life, and shorter life expectancy. Many people with dementia are prescribed antidepressants to treat depression, but it is uncertain how effective they are (Dudas et al., 2018).
Depression in older adults has been linked to dementia, although it is unclear whether it is a risk factor for dementia, or a prodromal symptom*. In some cases, depression and dementia may be caused by common risk factors such as cerebrovascular disease. In others, they may not have a connection at all and simply occur together by chance—as two separate neuropsychiatric diseases. Among depressed older adults, it is difficult to assess who may be at increased risk for developing dementia and, by extension, who would benefit from specific interventions to decrease this risk (Wiels et al., 2020).
*Prodromal symptom: a term used to describe a group of symptoms that may precede the onset of a mental illness. It is not a diagnosis.
Along with apathy, depression is one of the most common mood disorders in Alzheimer’s disease (Nowrangi et al., 2015). Almost one-third of long-term care residents have depressive symptoms, while an estimated 10% meet criteria for a diagnosis of major depressive disorder. In the long-term care population, depression is both common and under-treated (Jordan et al., 2014).
Depression, although frequently present in those with Alzheimer’s disease, is much more persistent in dementia with Lewy bodies. Depressive symptoms in Alzheimer’s disease and dementia with Lewy bodies are associated with a greater cognitive decline and, in Alzheimer’s disease, significantly relate to lower survival rates over a three-year period (Vermeiren et al., 2015).
Early Detection and Referral
The majority of patients with Alzheimer’s disease experience neuropsychiatric symptoms during the course of their disease. This can include include behaviors such as apathy, agitation, and psychosis, and are already highly prevalent in patients in the early stages of AD including those with mild cognitive impairment (Eikelboom, Singleton, van den Berg et al., 2019).
The majority of people with dementia currently do not receive a formal diagnosis. Only 20% to 50% of dementia cases in high income countries are recognized and documented in primary care, and this “treatment gap” is even greater in low- and middle-income countries. Early diagnosis of dementia is crucial since some treatments are more effective in the early stages, and earlier diagnosis and timely intervention provide health, financial, and social benefits (Ciblis et al., 2016).
Neuropsychiatric symptoms are very common in patients with mild cognitive impairment and Alzheimer’s disease dementia and are associated with various disadvantageous clinical outcomes, including a negative impact on quality of life, caregiver burden, and accelerated disease progression. Despite growing evidence of the efficacy of (non)pharmacological interventions to reduce these symptoms, neuropsychiatric symptoms remain underrecognized and undertreated in memory clinics (Eikelboom, Singleton, van den Berg et al., 2019).
Ultimately, the most successful model of treatment for Alzheimer’s disease will likely include early detection and control of physical factors (diabetes, hypertension, hyperlipidemia), followed by application of multifaceted, disease-modifying interventions to prevent the early and continued loss of neurons and to reduce the toxins that result in further cell deterioration (DeFina et al., 2013).