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The 3 Ds of Cognitive Impairment

The 3 Ds of Cognitive Impairment

When considering cognitive impairment in older adults, there are 3 Ds that are important to understand: dementia, delirium, and depression. These 3 Ds are all individual conditions, each with its own symptoms and features. However, they share a complex and interconnected relationship that can complicate diagnosis and treatment. [1] Understanding how the three relate to each other is essential to providing comprehensive care to individuals affected by them.

  1. Dementia: Dementia is an umbrella term used to describe a decline in cognition; symptoms can include changes in memory, attention, judgment, and language, and these changes must be severe enough to interfere with a person’s ability to carry out their daily tasks. [2] Dementia symptoms are caused by progressive, neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, or Frontotemporal Degeneration. With treatment, the progression of symptoms may be slowed, but they cannot be reversed or stopped. While dementia is not directly caused by depression or delirium, the presence of these conditions can worsen cognitive decline in dementia patients. Depression and delirium can often be misdiagnosed as dementia due to overlapping symptoms. 1 [3] [4] [5]
  2. Delirium: Delirium is a sudden and temporary state of severe confusion and cognitive impairment, often caused by underlying medical issues, medications, or surgery. With treatment, symptoms of delirium will typically be resolved. Delirium can mimic the symptoms of dementia, making it challenging to differentiate between the two. It can also trigger or worsen depression in vulnerable individuals. 2 3
  3. Depression: Depression is a common mood disorder characterized by persistent feelings of sadness, hopelessness, and a loss of interest or pleasure in activities. While it is a separate diagnosis from dementia and delirium, it often coexists with these conditions. Individuals with depression may be at higher risk of developing dementia in later life. 4 [6]

The Complex Relationship

Dementia, delirium, and depression are interconnected in various ways:

  1. Shared Risk Factors: All three conditions share some common risk factors, including age, genetics, and certain lifestyle choices. These factors can make it challenging to determine whether a person’s symptoms are primarily due to one condition, or a combination of them.
  2. Compounded Symptoms: Depression and delirium can manifest as cognitive impairment and memory problems, resembling the symptoms of dementia. 2 3 5 This overlap can lead to misdiagnoses and inappropriate treatment. Often, once a diagnosis of dementia, even an incorrect one, is given, it can be difficult to remove.  
  3. Interaction Effects: The presence of depression or delirium in individuals already diagnosed with dementia can worsen cognitive decline and functional impairment. It can also complicate the management of these conditions. 2 5
  4. Vicious Cycle: Depression can lead to social isolation and reduced physical activity, both of which are risk factors for dementia. Additionally, individuals with dementia are more susceptible to depression due to their cognitive decline and loss of independence. 


The relationship between delirium, depression, and dementia is complex. These conditions often coexist, creating challenges for diagnosis and treatment. Clinicians must consider the potential interplay of these conditions when evaluating and caring for individuals who present with cognitive and mood-related symptoms. Early diagnosis, appropriate interventions, and a holistic approach to care can help to improve the quality of life for those affected by these conditions. As research in this field continues, understanding the connections between these health issues will be imperative to determining strategies for prevention and treatment. 


[1] Downing, L.J., Caprio, T.V. & Lyness, J.M. Geriatric Psychiatry Review: Differential Diagnosis and Treatment of the 3 D’s - Delirium, Dementia, and Depression. Curr Psychiatry Rep 15, 365 (2013).\




[5] Tetsuka, S. (2021). Depression and Dementia in Older Adults: A Neuropsychological Review. Aging and Disease12(8), 1920-1934.



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