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.

4.1 How Dementia Affects Cognition

Dementia affects cognition because of loss of cells and connections in the parts of the brain that control thinking, memory, judgment, learning, language comprehension, attitudes, beliefs, safety awareness, morals, and planning ability. Dementia also affects motor and sensory functions such as balance, spatial awareness, vision, pain processing, and the ability to modulate (control) sensory input.

4.2 Potentially Treatable Conditions

There are many conditions that can cause dementia-like symptoms. Some of these conditions, such as infections, constipation, reactions to or interactions between medications, and abuse of alcohol, prescription medications, or recreational drugs are reversible with appropriate treatment.

Other potentially treatable conditions are more complicated and usually require additional evaluation and testing. This includes head injuries and subdural hematomas from falls and nutritional or fluid deficiencies. Physiologic conditions that are potentially treatable include:

• metabolic and endocrine abnormalities
• poisoning from exposure to lead, heavy metals, or other poisonous substances
• brain tumors, space-occupying lesions, and hydrocephalus
• hypoxia or anoxia (not enough oxygen)
• autoimmune syndromes 
• epilepsy
• sleep apnea (NINDS, 2023, December 19)

Delirium and depression—potentially treatable conditions that 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.

4.2.1 Delirium

Delirium has an acute onset and a fluctuating course. For patients with behavioral and psychological symptoms of dementia, delirium can cause an abrupt worsening of their usual symptoms. History is the key to differentiating these symptoms from delirium (Cloak and Khalili, 2022).

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, or metabolic changes. An unfamiliar environment, injury, or severe pain can also cause an episode of delirium.

Inattention is the most frequent clinical symptom in a delirium episode. Other symptoms include difficulty with orientation and memory, hallucinations, changes in language and thought, and visuospatial difficulties.

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).

4.2.2 Depression

Clinically, the most common diagnosis applied is major depressive disorder. This diagnosis includes at least one of two major symptoms—dysphoria* or anhedonia**. It can also include other symptoms such as sleep disturbances, feelings of guilt or worthlessness, changes in appetite, fatigue or reduced energy, agitation, suicidal ideation, and trouble concentrating or making decisions (Fisher et al., 2024).

*Dysphoria: feelings of discomfort, psychological distress, profound unease, or generalized dissatisfaction with life.
**Anhedonia: loss of interest in activities, an inability to experience pleasure.

Depression is a common mood disorders in Alzheimer’s disease. 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).

Diagnosing depression in patients with dementia can be difficult. Denial and cognitive impairment can compromise self‐report of depressive symptoms. And, as a person’s dementia progresses, the presentation of depression may change, with non‐verbal behaviors such as demanding behavior and clinging being more apparent than cognitive features (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. 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.

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).

4.3 Early Detection and Referral

In the context of dementia, early detection and a timely diagnosis is defined as “access to accurate diagnosis at a time in the disease process when it can be of most benefit to people with dementia and families.” In recent years, timely diagnosis has been emphasized as being more person-centered and respectful of individual rights than early diagnosis (Molvik et al., 2024).

Early detection provides an opportunity to identify causes, coordinate medical care, plan for the future, and address potential safety issues. Ideally, it connects families with interventions and identifies appropriate candidates for clinical trials of potentially disease-modifying therapies that are anticipated to benefit patients in early disease stages (Tsoy et al., 2021).

Early detection also provides opportunities to identify treatable or potentially reversible conditions. Unfortunately, cognitive impairment, including mild cognitive impairment and dementia, are frequently not detected in primary care, and diagnosis is delayed until moderate or advanced stages in 50% or more patients with greater delays among racial and ethnic minorities (Bernstein Sideman et al., 2022).

Being diagnosed with dementia significantly impacts a person’s life and can lead to worry and anxiety, post-traumatic stress, and even suicidal ideation. Nevertheless, some studies have suggested that being diagnosed with dementia can also provide psychological relief and promote healthy behaviors (Molvik et al., 2024).

There are racial/ethnic disparities in dementia incidence and prevalence, as well as social and medical risk factors for dementia. Undiagnosed dementia may be more common among racially/ethnically diverse individuals, particularly Black and Hispanic and Latino Americans compared with White Americans. In addition, beyond race/ethnicity, social determinants of health, comorbid medical conditions, and variability in health behavior patterns are likely associated with these inequalities (Tsoy et al., 2021).