Review: delusions in dementia

Age and Ageing,  Sept, 1996  by Richard J. Harvey

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Introduction

The definition of a delusion is `a false, unshakeable idea or belief ... held with extraordinary conviction and subjective certainty' [1]. Delusions are a common symptom of a range of psychiatric illnesses including schizophrenia, depression, bipolar disorder and dementia. The inclusion of dementia in this list is sometimes surprising to both doctors and carers, who restrict the symptoms of dementia to the cognitive domain; yet Alzheimer's first description was of a 51-year-old woman with focal cognitive deficits, delusions of jealousy and auditory hallucinations [2]. Considerable research has focused on the neuropathological findings, neuropsychological deficits and genetics of these diseases. It is only more recently that we have begun to untangle the non-cognitive or psychiatric features of the dementias.

More recently several factors have resulted in growing interest in this aspect of dementia. First has been the emergence of old age psychiatry as a discipline in its own right. In the UK every district now has psychiatrists with special responsibility for the care of older people with psychiatric illness, and clear guidelines exist for sharing the care of demented patients between them and geriatricians. The second factor has been social policy change. The focus of care for demented patients has shifted from hospital-based institutions to the community, with demented persons remaining in their own home supported by their families and community-based care. The presence of non-cognitive symptoms is very much less acceptable to family carers than memory or other deficits, and may significantly increase their burden. Finally, careful psychiatric assessment of patients with dementia may provide four-fold benefits: explanation and reassurance for the care-giver; the introduction of appropriate treatment for the patient; psychiatric symptoms may help to identify subtypes of dementia and estimate prognosis; and, scientifically, we may increase our understanding of the underlying functional, neuro-chemical and neuro-anatomical substrates of psychotic symptoms, with potential application to other psychiatric disorders.

Epidemiology

Delusional symptoms in dementia are common, with a prevalence of between 10% and 70% [3] and an annual incidence rate of between 1% and 5% [4]. The prevalence varies with the methodology of the study and the population being studied, with the highest rates being found when structured assessment instruments are used. Using data from ten studies involving 2787 patients with Alzheimer's disease defined by NINCDS/ADRDA [5] criteria, Allen and Burns [3] have calculated a weighted mean prevalence of delusions of 29.6% Some studies have shown that delusions are more common in patients with moderate cognitive impairment [6], while other studies have found no association with cognitive impairment [7]. It is possible that as the dementia progresses, either increasing language impairment prevents the person expressing their delusions or that the cognitive impairments may restrict the development of complex delusional ideas. There are limited data on length and resolution of symptoms; however a few small studies have demonstrated a resolution rate of 2% per year, with duration of symptoms between 2 and 4 years [4].

Categories of delusions

An understanding of the types and frequencies of the delusional ideas experienced by patients with dementia is useful both in recognizing symptoms reported by care-givers, and as an aide-memoire during history-taking and mental state examination. The Table gives a summary and brief description of the delusions most commonly found in dementia, with the approximate percentage of patients who experience each type of delusional idea. No formal classification of these symptoms exists, with a wide selection of categories being used by different studies. Classification is likely to be an important step in advancing research into the psychiatry of dementia.

Table. Common delusions in dementia

Type of delusion     Examples                            Approximate
                                                         prevalence
Theft                Complaints of people breaking          (%)
                     into the house to steal or
                     hide things                            22
Phantom boarder      Other people living in the house:
                     examples include the patient
                     laying extra places at the
                     table, or making extra cups of
                     tea                                    20
Persecution and      Beliefs that people are `out to
endangerment         get me', or that food is being
                     poisoned                               17
Spouse infidelity    `You are seeing someone else
                     behind my back'                         5
One's house is not   The person may ask `When are we
one's home           going home?' when they are in
                     their own home, or' if more
                     strongly held, may leave their
                     home in search of `home', which
                     may sometimes be a previous
                     address                                 5
Delusions of         The person believes that they or
infestation          their home is infested by small
                     organisms, e.g. spiders, worms,
                     lice or ants                            5
Picture sign         Believing their mirror image is
(A form of           someone else either in the
delusional           room or in a picture
misidentification)   The patient loses contact with
Delusions relating   the boundary between reality
to the television    and TV, believing that events
                     in the TV programme are
                     happening to the patient in
                     real life                               5
Abandonment          `You want to put me in a nursing
                     home'                                   4
Delusional           `You are not my husband, what
mix-identification   have you done with him?'--the
(Capgras and         belief that a familiar person
Fregoli              has been replaced by an imposter
syndromes)           who looks like the person               3
Delusions of love    The belief that a prominent,
(De Clerambault's    famous or otherwise unreachable
syndrome)            person is secretly in love with
                     them                                    1