Although one's core personality is thought to remain stable over the adult years, modest variation may arise in terms of its expression with advancing age. For instance, an increase in obsessive–compulsive traits is common among older people and may reflect not so much a change in intrinsic personality as an adaptation of the person to failing powers or altered relationships and environments (Engels et al, 2003). The neurological substrate of reduced adaptability has also been variously investigated in the context of cerebrovascular pathology (Stone et al, 2004) and falling levels of central neurotransmitters (e.g. dopamine; Volkow et al, 1998).

Personality disorder (Box 5.1) is a controversial concept, but the diagnosis remains pertinent in older people, provided that a suitable account of long-standing dysfunction can be established that pre-dates presentation. In simple terms, personality disorder may be construed as a long-standing pattern of maladaptive interpersonal behaviour (Kroessler, 1990). So, although it might be considered very late for the condition to present in old age (perhaps marking the culmination of many unhappy events for the individual), there might at least be the advantage of a considerable longitudinal history and pattern of behaviour for the examiner to investigate at the time of assessment.

Diagnosing personality disorders in older people is confounded by factors that are less likely to be present in younger age groups (Box 5.2).