The DSM-IV diagnostic criteria for schizoid and schizotypal personality disorders are shown in Tables 81-1 and

81-2. Many of the defining terms derive from the descriptors used by Mednick and Schulsinger (1968) in their Copenhagen study of children at high risk for schizophrenia. They drew up a large list of adjectives that could be condensed into two main factors: eccentricity (peculiar, odd, awkward) and introversion/schizoid (dreamy, shy, withdrawn). There are no essential differences between the criteria sets in DSM-III and DSM-IV.

Clinically, it is common for schizotypal patients to show, in addition, schizoid features. Paranoid and obsessive-compulsive traits are common to both groups. In general, schizotypal patients are more prone to peculiarities of thought or even to brief psychotic episodes and are thus closer conceptually to schizophrenia than are schizoid patients. Distinctions of this kind may help justify the compartmentalization into two categories of PD (schizoid and schizotypal), despite their similarities.

Schizotypal patients, from a clinical standpoint, often have comorbid paranoid PD. More than half of the patients in the study by Siever et al. (1991) showed this pattern. In the same series, only a few patients (<20%) diagnosed with paranoid PD did not meet the criteria for schizotypal PD. The regions of overlap within the eccentric cluster of PDs may be illustrated with a Venn diagram, as shown in

Figure 81-1.

In the study by Siever et al. (1991), for example, region VI (schizotypal × paranoid personality) would be more common than the “pure” types II and III. Because schizotypal patients often show schizotypal and paranoid traits simultaneously, region VII (schizotypal × schizoid × paranoid personality) would be well represented in a clinical series.

Epidemiologically, in contrast, there appears to be in the general population a number of paranoid persons with little in the way of schizotypal or schizoid traits. There are also some schizoid persons who, although inward and detached, function well in their occupations and are not inclined to seek therapy. Such patients show too few schizotypal or paranoid traits to be comorbid for those disorders by DSM criteria.