Hallucinations, Illusions, Delusions in Dementia: The Difference and What Might Be Done


People with dementia often experience the world in quite a different way to others  because of how they process what goes on.     This makes sense if we remember:

  • There may be changes in the brain that  affect the way that information received from the senses is processed.
  • The way that the person interprets what they are experiencing may also be compromised at a cognitive level.
  • Impairment to memory affects the context in which people, objects and events are perceived.
  • Changes to the senses caused by illness, prescribed or non prescribed drugs and normal ageing are very common.  Often people have deficits in multiple sensory areas.

Illusions, Delusions and Hallucinations:   What Are the Differences?

  • Illusions:  Illusions occur because of misinterpretation of sensory information.  Someone might hear the radio and think that there is a person in the room with them, view a reflection or shadow as a real object, mistake an inanimate object in the environment for a person or something threatening.  These can also lead to the person misconstruing environment cues such as believing changes in floor surfaces might put them at risk of falling.    I think at some stage that this has happened to us all but may occur more frequently if a person has dementia combined with sensory deficits.  The physical environment including lighting levels can  contribute to this confusion.  A person’s emotional state might also be a factor. For example if someone is anxious they may be much more  likely to interpret the world around them as a hostile place.
  • Hallucinations:  These are sensory experiences that have no external stimuli.   They can occur in all dementias but are a more common feature of   Lewy body disease and those related to Parkinson’s disease.  Seeing things that aren’t there is the most common sort of hallucination experienced by people with dementia.  However a person may experience hallucinations related to other senses, for example, hearing, smell or taste.  Tactile symptoms such as being crawled over by insects, are rarer but not out of the question.
  • Delusions:   A person maintains fixed beliefs that are not based on reality.  This can cause paranoia and present barriers to providing necessary care These can be distressing for all parties concerned.  False accusations about stealing fall into this class as are beliefs that another person is out to do them harm (although do not rule out these claims altogether as they may be couched in reality).  Other examples include  overestimating  self abilities which might lead to excessive risk taking.   Erroneous views about the nature of relationships are common, for example failure to acknowledge  their partner or  believing that their child or a family friend is their spouse.  Confusion around when events took place over a lifespan can cause a person to have distressing thoughts.  For instance they might believe that their children are young and are missing from the home or in danger or that a parent has deserted them.

A person’s skewed perception of the world will seem very real to them.   Occasionally they might accept explanations that their distorted version of reality is ‘their mind playing tricks on them’.  However  if this is not the case, lengthy arguments to try and correct them will not be successful and are likely to lead to upset.

Sometimes these states of mind are benign and even comforting.  For example, I’ve met quite a few people in my career who are not at all concerned that they are hallucinating a fluffy animal or small children.  In many circumstances  however, these altered mind states can cause considerable distress, both to the person and those who support them.

Action to Take

Even if  altered perceptions or beliefs are not causing any upset  I would recommend that professional advice is sought if a person with dementia is hallucinating or misconceiving the physical and social environment in which they live .  Provide information about their nature,  what time of day that symptoms are most likely, where they occur if they seem to be specific to particular places, whether the onset has been sudden or gradual and how the person reacts.

These misperceptions may be attributable to the brain changes in dementia and as such may change over time.  However other causes should be explored for,  in some instances, the situation might be rectified or improved.  Physical illness, particularly infections, dehydration and adverse reactions to medication may bring on the sudden onset of symptoms.  Pre-existing or newly emergent mental health conditions other than dementia might also be the culprit.     Features in the person’s physical environment or sensory deficits also merit exploration.

Whilst medication is sometimes part of the answer  it is not often advocated as the first line of approach for treatment.  There are other things to try including sensory approaches and changes to the environment, activities and care.   Seek advice from a dementia specialist as the issues that are affecting a particular individual may be complex to unpick.

Whilst many strategies can be helpful it should also be acknowledged that there is not always a easy solution.  These circumstance can be particularly stressful for carers who will, in most cases, benefit from additional education and support.

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