Dementia

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

Dementia is a syndrome resulting from acquired brain disease. It is characterized by a progressive decline in memory and other cognitive domains that, when severe enough, interferes with daily living and independent functioning.

This definition is consistent with the diagnostic category, major neurocognitive disorder (major NCD), as defined in the Diagnostic and Statistical Manual of Mental Disorders–5th Edition (DSM-5; American Psychiatric Association [APA], 2013). The diagnostic criteria for major NCD are

  • a significant decline from previous levels of performance in one or more cognitive domains, including complex attention, executive function, learning and memory, language, perceptual motor, or social cognition (preferably documented by standardized testing or clinical assessment);
  • cognitive deficits interfere with independence in everyday activities;
  • cognitive deficits do not occur exclusively in the context of delirium; and
  • cognitive deficits are not better explained by other mental disorders, such as major depressive disorder or schizophrenia (APA, 2013).

Behavioral problems (e.g., paranoia, hallucinations, and repetitiousness) may also develop as a result of the neuropathology and may interfere with communication.

Cognitive and behavioral symptoms of dementia are differentiated from those of temporary or treatable conditions, including the following: 

  • 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, including
    • infections (e.g., urinary tract infection [UTI], meningitis, syphilis);
    • toxicity (e.g., drug-induced dementia, toxic metal exposure);
    • vitamin B-12 deficiency;
    • metabolic disorders (e.g., kidney failure);
    • hormonal dysfunction (e.g., thyroid problems); and
    • pseudodementia due to psychiatric disorders (e.g., depression, generalized anxiety disorder, schizophrenia, mania, conversion disorders).

Unlike these conditions, the symptoms associated with dementia continue to progress in severity until death (see, e.g., Bourgeois & Hickey, 2009). The following are common neurodegenerative diseases that cause dementia. This list is not exhaustive.

  • Alzheimer’s disease (leading cause of dementia) 
  • Lewy body disease
  • Vascular pathology (e.g., multi-infarct dementia)
  • Frontotemporal dementia (FTD)—Pick’s disease (behavioral variant) and primary progressive aphasia (language variant)  
  • Huntington’s disease
  • Parkinson’s disease

See ASHA’s resource on common dementias.

Other conditions that may 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);
  • multiple sclerosis; and
  • human immunodeficiency virus (HIV). 

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).

Some older adults report a decline in cognitive abilities that may not be evident upon objective cognitive testing (Jessen et al., 2014). This subjective cognitive decline is associated with an increased risk of progression to mild cognitive impairment (MCI) and dementia (Jessen et al., 2014). 

MCI is described as an “intermediate stage of cognitive impairment that is often, but not always, a transitional phase from cognitive changes in normal ageing to those typically found in dementia” (Petersen et al., 2014, p. 214). Early identification of MCI might enable the use of cognitive interventions to slow the progression of decline (Qualls, 2005). See section in this Portal page on modifiable risk factors.

Unlike dementia, the cognitive decline associated with MCI does not interfere with independence in everyday activities (see, e.g., McKhann et al., 2011). This definition of MCI is consistent with the diagnostic category, mild neurocognitive disorder (mild NCD), as defined in the DSM-5 (APA, 2013). The clinical criteria for diagnosing mild NCD are

  • a modest decline from previous levels of performance in one or more cognitive domains, including complex attention, executive function, learning and memory, language, perceptual motor, or social cognition (preferably documented by standardized testing or clinical assessment);
  • cognitive deficits do not interfere with the ability to independently perform everyday activities (although some may require greater effort or use of compensatory strategies),
  • cognitive deficits do not occur exclusively in the context of delirium, and
  • cognitive deficits are not better explained by other mental disorders, such as major depressive disorder or schizophrenia (APA, 2013).

See ASHA’s Mild Cognitive Impairment Evidence Map for summaries of the available evidence on this topic.

Early Onset Dementia

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), lack of awareness about the condition—even among health care professionals (Jefferies & Agrawal, 2009), and misdiagnosis (van Vliet et al., 2011). In addition, some causes of EOD are curable (e.g., infection, metabolic toxins), which makes the need for timely and accurate diagnosis even more crucial (Fadil et al., 2009). 

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