See the Dementia Evidence Map for summaries of the available research on this topic.

Dementia is a syndrome resulting from acquired brain disease and characterized by progressive deterioration in memory and other cognitive domains (e.g., language, judgment, abstract thinking, and executive functioning). Although the cognitive profiles of individuals diagnosed with dementia vary somewhat by etiology, the degree of deterioration represents a decline from previous levels of functioning and is sufficient to interfere with social and occupational functioning.

The cognitive decline associated with dementia affects an individual's ability to comprehend and produce linguistic information. Additionally, behavioral problems that develop as a result of the neuropathology (e.g., paranoia, hallucinations, and repetitiousness) may interfere with communication.

The cognitive and behavioral symptoms of dementia are differentiated from those of

  • delirium, an acute state of confusion associated with temporary, but reversible, cognitive impairments (Mahendra & Hopper, 2013);
  • age-related memory decline;
  • other conditions that have inconsistent symptoms or are temporary and/or treatable (Bourgeois & Hickey, 2009), including
    • infections (e.g., urinary tract infection [UTI], meningitis, syphilis),
    • toxicity (e.g., drug-induced dementia, toxic metal exposure),
    • pseudodementia due to psychiatric disorders (e.g., depression, generalized anxiety disorder, schizophrenia, mania, conversion disorders).

In contrast to these conditions, the symptoms associated with dementia continue to progress in severity until death (Bourgeois & Hickey, 2009). Neurodegenerative diseases that result in dementia include

  • Alzheimer's disease,
  • Lewy body disease,
  • vascular pathology (e.g., multi-infarct dementia),
  • frontotemporal lobar degeneration (e.g., Pick's disease and primary progressive aphasia),
  • Huntington's disease,
  • Parkinson's disease.

Other conditions that result in dementia due to progressive changes in brain function include

  • Wernicke-Korsakoff syndrome secondary to chronic alcohol abuse,
  • traumatic brain injury (TBI),
  • chronic traumatic encephalopathy due to repeated trauma (e.g., dementia pugilistica),
  • chemotherapy (Kean & Locke, 2008),
  • multiple sclerosis,
  • human immunodeficiency virus (HIV).

See detailed information about common dementias.

Primary Versus Secondary Dementia

Primary dementias are those—like Alzheimer's disease (AD), multi-infarct dementia, and dementia with Lewy bodies—in which the dementia itself is the major sign of an organic brain disease not directly related to any other organic illness. Secondary dementias are those caused by, or closely related to, some other recognizable disease, such as HIV, head injury, multiple sclerosis, or chronic alcohol abuse.

Mild Cognitive Impairment

There is evidence that neuropathological changes occur well in advance of clinical manifestations of Alzheimer's dementia (Bennett et al., 2006), and subtle cognitive deficits occur up to 9 years prior to the diagnosis (Amieva et al., 2005). These and similar findings have led to the concept of mild cognitive impairment (MCI), described as a transitional stage between normal aging (i.e., age-associated memory impairment) and dementia (Bourgeois & Hickey, 2009; Qualls, 2005). Individuals diagnosed with MCI are at greater risk of developing dementia; early identification of MCI might enable the use of cognitive interventions to slow the progression of decline (Qualls, 2005).

MCI is consistent with the diagnostic category, Mild Neurocognitive Disorder, defined in the Diagnostic and Statistical Manual of Mental Disorders-5th edition (DSM-5; American Psychiatric Association, 2013). The clinical criteria for diagnosing MCI are

  • subjective complaints or concerns about cognitive changes corroborated by an informant,
  • impairment in one or more cognitive domains relative to age and educational level (preferably documented by standardized testing),
  • essentially normal activities of daily living (although some may require greater effort or use of compensatory strategies),
  • absence of dementia—changes are mild with no significant social or occupational impairment.

(Albert et al., 2011; American Psychiatric Association [AMA], 2013; Bourgeois & Hickey, 2009; Key-DeLyria, 2013; Mahendra & Hopper, 2013)

Early Onset

Dementia is typically associated with the elderly population. However, dementia can affect younger individuals. Early-onset dementia (EOD) refers to dementias that occur before the age of 65.

Differential diagnosis of EOD is complicated by the fact that symptoms may be more variable in younger patients than in the elderly, due to different etiologies (McMurtray, Clark, Christine, & Mendez., 2006; Fadil et al., 2009) and a lack of awareness about the condition, even among health care professionals (Jefferies & Agrawal, 2009). In addition, some causes of EOD are curable, which makes the need for timely and accurate diagnosis even more crucial (Fadil et al., 2009).

The needs of younger individuals with dementia are different from those of individuals with late-onset dementia. EOD often affects individuals who are working and have dependent families and significant financial responsibilities, and services and supports for these individuals are complex and require input from a multidisciplinary team (Jefferies & Agrawal, 2009). Early diagnosis allows for early treatment, access to appropriate supports, and long-term preparation and planning for the family.

Relationship Between Hearing Loss and Dementia

Approximately one third of Americans between the ages of 65 and 74 and nearly half of those over the age of 75 have hearing loss (National Institute on Deafness and Other Communication Disorders [NIDCD], 2010). Many older adults will have both hearing impairment and cognitive loss, and, together, these losses will affect communication, social participation, and quality of life (Pichora-Fuller, Dupuis, Reed, & Lemke, 2013).

Lin et al. (2013) found that individuals with baseline hearing loss had greater rates of cognitive decline over time than individuals with normal hearing. Further investigation is needed to clarify this relationship and to determine whether or not hearing loss is a risk factor for dementia. One hypothesis is that when a hearing loss is present, greater cognitive resources are dedicated to auditory processing, leaving fewer resources for other cognitive processes, like working memory (Peelle, Troiani, Grossman, & Wingfield, 2011). Recent research suggests the possibility of a shared etiological pathway responsible for both hearing loss and dementia (Gallacher et al., 2012)

It is important for clinicians to differentiate between hearing loss and cognitive impairment and to identify when one or both of these conditions are present.

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