Estimates of the point-prevalence of paranoia and other psychotic symptoms among persons age ≥65 years have ranged from approximately 4 per cent to 6 per cent,^(1,2,3) and may be as high as 10 per cent among those age ≥85 years.⁽⁴⁾ Although the majority of these symptoms occur as secondary psychoses in the context of Alzheimer’s disease or related dementias,⁽⁵⁾ the population of people with schizophrenia is ageing along with the general ‘greying’ of the industrialized world, and mental health care for older adults with schizophrenia is expected to be an increasingly important public health concern.⁽⁶⁾

Schizophrenia is typified by the presence of two or more of the following categories of core symptoms: delusions, hallucinations, disorganized or catatonic behaviour, disorganized speech (or formal thought disorder), and negative symptoms (such as affective flattening, avolition, or social withdrawal).⁽⁷⁾ Older patients tend to have less severe positive symptoms (hallucinations, delusions, disorganized behaviour) than their younger counterparts, but there are few age-related differences in presence or severity of negative symptoms.^(8,9)

Most patients with schizophrenia and related primary psychotic disorders also have mild to moderate neurocognitive deficits.⁽¹⁰⁾ There is considerable interpatient heterogeneity in terms of the severity of neuropsychological deficits, but the level of these deficits is a consistent and strong determinant of impairments in everyday functioning⁽¹¹⁾ and competence or decisional capacity.⁽¹²⁾

In terms of late-life schizophrenia, one common division is between those with earlier onset in adolescence or early adulthood (prior to age 40 or 45 years) versus later-onset (onset ≥age 40 or 45 years). The latter group may comprise as many as 24 per cent of people with late-life schizophrenia.⁽¹³⁾ Relative to similarly aged patients who had earlier onset, those with later-onset schizophrenia tend to have a higher prevalence of paranoid subtype and persecutory delusions, but better premorbid social-occupational functioning, fewer current disorganized symptoms, less severe (although not an absence of) negative symptoms, and less severe neuropsychological impairment. They are also more likely to be women, and tend to respond to lower doses of antipsychotic medication.^(3,14,15) The two groups are similar in terms of severity of thought disorder,⁽¹⁶⁾ although patients with very late onset schizophrenia-like psychosis (age of onset ≥60 years) tend to have less severe formal thought disorder.⁽¹⁷⁾

The term ‘schizophrenia’ was coined by Eugen Bleuler in the early 20th century, but he wrote of ‘the schizophrenias’ (plural)⁽¹⁸⁾ as an
explicit acknowledgement of the substantial heterogeneity that characterizes this condition. Efforts to group ‘the schizophrenias’ into meaningful subtypes have been a key part of efforts to define the syndrome itself.⁽¹⁹⁾ Most of the terms describing different subtypes of schizophrenia in the current Diagnostic and Statistical Manual (DSM-IV-TR)⁽⁷⁾ and in the International Classification of Diseases (ICD-10)⁽²⁰⁾ [such as paranoid, catatonic, hebephrenic (disorganized), and undifferentiated (simple) subtypes] overlap with the subtypes identified by Kraepelin and or E. Bleuler a century ago. Other subtyping efforts have focused on a variety of dimensions such as positive and negative symptoms, cognitive functioning and/or course, but as true of the clinical subtypes in the DSM-IV-TR and ICD-10, there is invariably substantial intrasubtype heterogeneity.⁽²¹⁾

In regard to late-life schizophrenia, one of the key nosological controversies over the past century has been whether or not the late onset form is actually schizophrenia. Kraepelin’s conception of dementia praecox in 1896 was that the disorder was defined by onset in adolescence or early adulthood. By 1913, Kraepelin came to acknowledge that early onset was not a universal feature, but the emphasis on early onset remained a potent belief in the field throughout most of the 20th century.⁽²²⁾ On the other hand, interest in late-onset schizophrenia has a long history, including seminal work by Manfred Bleuler, begun in the early 1940s with patients whose symptoms emerged at or after age 40 years.⁽²³⁾

The term ‘late-onset schizophrenia’ has occasionally been used interchangeably with the term late paraphrenia, although the latter was originally conceptualized as a more circumscribed psychosis with onset at age 60 or 65.^(24,25) Unfortunately, the terms ‘late-onset schizophrenia,’ and paraphrenia (with or without the epithet ‘late’), and a variety of age cut-offs have been used interchangeably and inconsistently over the years, resulting in considerable confusion in the literature.^(22,25) In a 1998 international consensus meeting on this topic, the group consensus suggestion was that the term ‘late onset schizophrenia’ be reserved for those with onset between ages 40 and 59 years, whereas the term ‘very late onset schizophrenia-like psychosis’ be used with those whose symptoms first manifest at age 60 or later.⁽³⁾

None of the above schizophrenia onset-related categories is represented in the contemporary formal diagnostic systems. The 1980 version of the American Psychiatric Association’s Diagnostic and Statistical Manual (DSM-III)⁽²⁶⁾ arbitrarily excluded the diagnosis of schizophrenia if symptoms did not emerge prior to age 45. This exclusion was dropped from the subsequent revision (DSM-III-R),⁽²⁷⁾ although the DSM-III-R required the specification of ‘late onset’ if the prodromal phase of illness developed after 45. The latter is the only instance of ‘late-onset schizophrenia’ appearing as a named condition in one of the major nosological systems. Based on mounting empirical evidence that ‘real’ schizophrenia could manifest after age 45,⁽¹³⁾ the age of onset restrictions as well as the ‘late onset’ specifier were dropped in the DSM-IV ⁽²⁸⁾ and DSM-IV-TR.⁽⁷⁾ Similarly, there is no age-of-onset related restriction or specification under the ICD-10.⁽²⁰⁾

The diagnostic criteria for schizophrenia in the DSM-IV-TR and ICD-10 mention neither current age nor age of onset.^(7,20) A key differential diagnosis with older adults is to rule out presence of a secondary psychosis.⁽²⁹⁾ For instance, among elderly patients, psychotic symptoms most commonly present in the context of dementia, such as Alzheimer’s disease, Parkinson’s disease, or dementia with Lewy Bodies.⁽⁵⁾ The pattern in any one patient may of course vary from normative trends, but in general among those with dementia-related psychotic symptoms, there is a greater propensity for visual over auditory hallucinations, and bizarre content is less common in the delusions than in those of patients with primary psychotic disorders such as schizophrenia.⁽³⁰⁾

Delirium may also present as acute psychosis;⁽³¹⁾ as with dementia, visual hallucinations and delusions tend to be more common than auditory hallucinations, but the psychotic symptoms associated with delirium can be of any form.⁽³²⁾ Given the high rates of polypharmacy among the elderly as well as age-related changes in pharmacokinetics, it is also important to consider potential acute mental effects of the medications in isolation and in combination.⁽³³⁾ Other differential diagnoses to consider among elderly patients are non-psychotic hallucinations related to bereavement or sensory deprivation.^(34,35)