WHEN BRIAN BLACKWELL was convicted of the manslaughter of both his elderly parents, it was on the basis of diminished responsibility because of narcissistic personality disorder. Blackwell, 19, been an exemplary student at school and was on the brink of starting as a medical student at Nottingham University when he stabbed his parents, then stole their credit cards, moved in with his girlfriend and went on a spending spree.

Personality disorders are often apparent in adolescence or even childhood and likely to become less pronounced in old age. People with a diagnosable personality disorder suffer psychological traits that lead to a persistent pattern of abnormal behaviour (without its being psychotic, or their having definable psychiatric disease). It interferes with the person’s reaction to his or her environment. People with some personality disorders are maladjusted but, even so, their symptoms may occasionally even help them to be outwardly successful in their work. Conversely, other personality disorders are incompatible with a satisfactory career. Almost invariably, personality disorders militate against good relationships; a sufferer’s personal life is likely to be not only unsuccessful but often disastrous.

Eleven types of personality disorders are recognised in the Diagnostic and Statistical Manual of Mental Disorders (DSM), an internationally recognised manual of psychiatric diseases and psychological problems. The disorders are grouped into three clusters. Blackwell’s personality disorder, the narcissistic personality, is in the second group. This includes psychopathy (the antisocial personality disorder), the borderline personality disorder (total instability of mood with impulsiveness and inappropriate emotional response coupled with an inability to make stable relationships), the histrionic personality disorder (an excessively self-centred approach to life that demands attention and praise, its many other symptoms include contrived and exaggerated emotions), and Blackwell’s narcissistic personality.

People are not described as having a personality disorder if their symptoms are so minor that they don’t impinge on their emotional relationships or professional life — or if they are so transitory that the person is able to adapt well to society (even if they are a bit too pleased with themselves).

The narcissistic personality disorder is one that is not diagnosed in children or young adolescents; there is an assumption that some of its traits are common in these age groups, and that most people at that time of their lives are to a greater or lesser extent self-centred. Many other people have some degree of narcissism, but don’t have the necessary accumulation of symptoms that leads to a diagnosis of this disorder. The DSM lists giveaway symptoms: in the case of the narcissistic personality disorder there are nine telltale symptoms. To have one or two of these is not unusual, but those who have more than five are not only difficult to have around house or office, but might justifiably be described as having a personality disorder.

Look out for:

1 A grandiose sense of self-importance. The person exaggerates his or her own abilities and accomplishments, and expects to be recognised as rather “special”.

2 The belief that only he (it is usually he) has unique problems and that these could be understood only by other people as elevated as he thinks he is.

3 A need for excessive admiration: they are for ever waiting to hear the compliments they think they deserve.

4 A sense of entitlement not justified either by their attainments or situation. For example, they expect the best table in the restaurant as of right, the best room in the hotel, quick and deferential service, and can think of no reason that they should queue even if everyone else is having to.

5 The belief that if only their hitherto unhonoured achievements and ability were noted, their success and power would be limitless.

6 Reacting to criticism with inappropriate rage or unnecessary humiliation. The person has feelings that either they are hopeless and a criticism was more than justified, or that it was unjustified and displayed a lack of understanding of the circumstances.

7 A lack of empathy (or they may fake it if their job and promotion requires it). This means that the person with a narcissistic personality disorder either doesn’t understand someone else’s needs, or if they do, are indifferent to them.

8 Arrogance and haughtiness.

9 Willingness to exploit other people to achieve their own goals. They are therefore prepared to sacrifice others for the greater good of somebody who matters — they themselves.

It is easy to understand that some of the symptoms of narcissism are very like those that appear in the description of the other personality disorders in the same cluster. There is a considerable crossover of symptoms and this leads to some doctors dismissing the whole concept of separate personality disorders. Likewise, many of the symptoms of personality disorders are also present in psychotic patients, and may be the only obviious symptons of an underlying psychiatric disease.

The judge ordered that Blackwell should serve at least six years and admitted to having doubts as to whether he would ever be well enough to be released. Treatment of all personality disorders is often a failure. Blackwell’s best hope of ever having a free life would be for a treatable psychiatric condition to be uncovered.