What is the difference between dementia and Alzheimer’s disease?

Find out the difference in the symptoms of Alzheimer's disease and dementia.

There is often confusion regarding the difference between dementia and Alzheimer's disease. Alzheimer's disease has some distinctive symptoms that are different from those of dementia.

For one, we often think of forgetfulness in elderly as a normal sign of ageing. And when the forgetfulness progresses to advanced stages, we tend to call it dementia. But dementia as such is not an illness, it is actually a group of symptoms. So the main difference between dementia and Alzheimer's disease is that dementia is a group of symptoms caused by a disease, and Alzheimer's is a disease.

What is dementia?

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According to the Diagnostic and Statistical Manual for Mental Disorders (DSM-IV), dementia is defined as a 'decline in memory with impairment of at least one other cognitive function, such as skilled movements, language or executive function such as planning, attention and abstract reasoning'. The manual also adds that this decline cannot be because of other psychiatric conditions such as depression, mood disorders, or psychosis. [1]

Symptoms of dementia

Common symptoms of dementia include

- Memory loss

- Noticeable decline in communication skills

- Disorientation to time and place

- Difficulty with abstract thinking

- Faulty reasoning and confusion

- Impaired judgement

- Gait and balance problems

Typical ageing also involves memory loss but it is different from that of dementia, in the sense, people with dementia will not be able to recall specific instances; they will be more confused; they will be frequently pausing while speaking to find the right word; they might even get lost in familiar places.

Certain types of dementia can be slowed down or reversed if identified in time. But therein lies the problem. It is difficult to identify the signs of early dementia, and especially so in India.

In one study, researchers from West Bengal reported that recognising early dementia cases in India is problematic as forgetfulness is seen as natural part of ageing, and as the responsibility of household activities, money transactions, and high-pressure work is shouldered by the younger generation in the family, early dementia in the elderly goes undetected. [2]

Risk factors for dementia

In general, the risk factors for dementia are

- Age

- Trauma

- Family history

- Illiteracy

- Lifestyle diseases such as hypertension and diabetes

- Stroke

- Poor nutrition, drugs and alcohol

- Poor socioeconomic status

However, one of the main causes of dementia are medical conditions, such as Alzheimer's, Parkinson's disease, and Huntington's disease, which attack brain cells. These diseases also constitute the types of dementia.

Types of dementia

  1. Alzheimer's disease: This is the most common type of dementia. Here, chemistry and structure of the brain changes, causing the death of brain cells.
  1. Vascular dementia: When the oxygen supply to the brain fails, for example, following a stroke, the brain cells die leading to vascular dementia.
  1. Lewy body dementia: In this type of dementia, tiny spherical structures called Lewy bodies develop inside nerve cells causing degeneration of brain tissue.
  1. Fronto-temporal dementia: Also known as Pick's disease, this type of dementia damages the front part of the brain affecting the personality and behaviour of the person.

Rarer causes of dementia include Parkinson's disease, Huntington's disease, multiple sclerosis, central nervous system infections, mild cognitive impairment, HIV-related cognitive impairment, and Korsakoff's syndrome associated with heavy drinking for a long time.

How does Alzheimer's disease develop?

Although scientists are not sure what exactly causes Alzheimer's disease, they believe plaques and tangles are in some way associated with the loss of brain tissues. Abnormal clusters of 'sticky' proteins called plaques start building up between nerve cells in the brain much before the onset of the Alzheimer's disease. These plaques block the cell-to-cell signalling in the brain and cause cell death. The plaques also activate the immune system cells that trigger inflammation.

Tangles are abnormal twisted fibres of protein, called tau, found inside nerve cells. In healthy cells, tau helps transport nutrients and other cellular components in the nerve cells. Scientists have found that the tangles are formed when very high amounts of phosphate molecules attach to tau, causing the tau threads to enmesh with each other, collapsing the transport system inside parts of the brain.

Many people develop plaques and tangles when they age, but in people with Alzheimer's disease, the concentration of these proteins is abnormally high. Plaques and tangles begin in the areas of the brain associated with learning and memory, and gradually spread to other regions of the brain.

Symptoms of Alzheimer's disease (AD)

  1. The earliest symptoms of AD is memory loss. The person with AD may have difficulty

- recalling recent events

- forgetting familiar routes or names

- lose items, such as keys or glasses, around the house

- learning new information

However, people with AD may recall life events that happened long time ago.

  1. As the disease progresses, memory loss starts interfering with the daily activities. Moreover, problems with other aspects of thinking, communication, and orientation start to develop. People with AD forget where they are or how they got there. They find it difficult to find the right word. Vocabulary becomes hard.
  1. Vision changes occur. For example, judging distances becomes harder, telling the colours apart becomes harder, or reading small prints is harder.

These are all dementia symptoms. However, AD has additional symptoms apart from the above-mentioned symptoms. Although AD is considered to be a cognitive disorder, people with AD show neuropsychiatric symptoms during later stages of the disease.

Almost 80 to 90 percent of people with AD exhibit mild to severe neuropsychiatric symptoms or non-cognitive symptoms. Mild symptoms include depression, apathy, anxiety, and irritability; whereas, severe symptoms include aggression, agitation, hallucination and disinhibition. These symptoms persist or recur over time, causing much distress to the caregiver, so much so, the patient may require institutionalisation. [3]

Of all the neuropsychiatric symptoms, depression and apathy are the most frequently observed symptoms in people with AD. Verbal and physical agitation is also common.

People with late-onset AD may also develop psychosis in the form of delusions and hallucinations, as the disease progresses. Studies have shown that delusions could be of persecution, infidelity, abandonment, and the belief that deceased individuals are still alive. Sometimes, it could be misidentification delusions, for example, believing there are phantom boarders in the house, or believing that their spouse is a stranger and not their husband /wife. Hallucinations in AD are typically visual, for example, where the person may see bugs crawling up the leg, or have visions of the past. [4]

Another symptoms specific to AD is the disturbance in sleep /wake cycle. And sleep disturbances often increase as the disease progresses. A person with AD may have daytime drowsiness and sleepless nights, which may further cause depression and agitation, or they may have round-the-clock naps instead of proper night time sleep. According to a study, 25 50 percent of people with AD have major sleep problems, and almost 75 percent sleep for extended periods during the day. [5]

Maybe, the dementia in Alzheimer's disease is irreversible, but with proper care and management, people with Alzheimer's disease can have a better quality of life.

"While no one can change the outcome of dementia or Alzheimer's, with the right support you can change the journey." - Tara Reed, in her book 'What to Do between the Tears'


  1. Scott KR, Barrett AM. Dementia syndromes: evaluation and treatment. Expert review of neurotherapeutics. 2007;7(4):407-422. doi:10.1586/14737175.7.4.407.
  1. Das SK, Pal S, Ghosal MK. Dementia: Indian scenario. Neurol India 2012;60:618-24.
  1. Nowrangi M, Lyketsos C, Rosenberg P. Principles and management of neuropsychiatric symptoms in Alzheimer's dementia. Alzheimers Res Ther. 2015;7(1):12. doi:10.1186/s13195-015-0096-3.
  1. DeMichele-Sweet MA, Sweet RA. Genetics of Psychosis in Alzheimer Disease: A Review. Journal of Alzheimer's disease : JAD. 2010;19(3):761-780. doi:10.3233/JAD-2010-1274.
  1. Lyketsos CG, Carrillo MC, Ryan JM, et al. Neuropsychiatric symptoms in Alzheimer's disease. Alzheimer's & dementia : the journal of the Alzheimer's Association. 2011;7(5):532-539. doi:10.1016/j.jalz.2011.05.2410.

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