55% of the examined patients with a clinical diagnosis within the schizophrenia spectrum qualified for one or more diagnoses of personality disorder according to the SCID-5-PD, most frequently BPD. Interestingly, SPD was not found in 7 of 10 patients clinically diagnosed with schizotypal disorder. These findings are in line with the study by Zandersen and Parnas cited in the background section(8). Additionally, Moore, Green and Carr(13) studied a large sample of patients diagnosed with schizophrenia (n=549). The participants were screened with the International Personality Disorder Examination Questionnaire (IPDEQ)(14) and outcomes were compared to those of healthy controls. The study found that patients suffering from schizophrenia were 8 times more likely to screen positive for a personality disorder than a healthy control. Patients with schizophrenia were also more likely to screen positive for personality disorders across clusters than healthy controls. While these results are similar to ours, they are interpreted as co-morbidity and linked to specific prognostic outcomes. There is little discussion regarding the possible connection between the altered personality and the underlying condition of schizophrenia. Our findings too could be understood as a reflection of co-morbidity, i.e. the personality disorders are co-morbid to schizophrenia. However, co-morbidity in ICD-10 is only relevant for disorders that are not aspects of the same clinical entity. SSD patients often exhibit disturbances that superficially mimic personality disorders but are, in fact, expressions of a more profound psychopathology(15,16).
It is not always clear what kind of phenomena the diagnostic criteria for a personality disorder cover. An example of this is the BPD criteria of “identity disturbance” and “chronic feelings of emptiness” that can be interpreted at different levels. At a personal or narrative level, identity disturbance can reflect confusion regarding career choices, social and romantic relationships etc., whereas identity disturbance at the level of the minimal or core self reflects “[…] distortions of first-person perspective, incomplete sense of substantiality-embodiment, and an ephemeral sense of self-presence”(17). These are psychopathological phenomena often seen in patients with SSD. Similarly, feelings of emptiness at the narrative level can refer to a lack of values or direction in life. At the level of the minimal self, these feelings reflect different kinds of depersonalization linked to SSD(17). As the SCID-5-PD contains no instructions or tools for differentiating psychopathology at a structural level, it is possible for patients with SSD to be misdiagnosed with a personality disorder. This may result in a patient not getting indispensable antipsychotic medication.
The potential mistake of overlooking a condition of schizophrenia may not be a weakness inherent to the design of the SCID-5-PD. This interview is not meant to differentiate between broad categories of psychiatric illnesses, but only to assess personality disorders as described in the DSM-5. However, in clinical work the SCID-5-PD is often used as sole diagnostic instrument when a diagnosis of personality disorder is suspected. It is difficult to find quantitative data of the extent of such sub-optimal clinical practices. The user guide of the SCID-5-PD itself presents an example. This is a clinical case, meant to serve as a tutorial of how the interview should be conducted. In this scenario, a young man is referred to the psychiatric department by his general practitioner, after he unexpectedly bursts into tears during a routine check. Upon entering the psychiatrist’s office, he exhibits unusual behaviour, including displaying a copy of a dollar bill with the patient’s face glued on instead of George Washington’s (2).
If any sort of general psychiatric assessment is performed, mention of it is omitted in the user guide. The patient is assessed with the SCID-5-PD and given multiple diagnoses of personality disorder.
A different problem may arise when a psychotic condition is established prior to the administration of the SCID-5-PD. In this case, answers are considered invalid if they exclusively relate to events occurring during psychotic or affective episodes. According to the SCID-PD guidelines the interviewer is supposed to ask directly if the answers provided occur outside these episodes(11). This question presupposes that the patient knows what is meant by the term “psychosis” and can delimit psychotic states temporally. This distinction, if at all possible, requires a high level of insight into illness(18). Although there is no consensus on the definition of the concept of insight into illness, it is generally recognized that schizophrenic patients frequently suffer from a lack thereof(19).
The diagnostic criteria in DSM-5 and ICD-10 are meant to delimit the different mental conditions, not to be comprehensive descriptions of the psychopathology inherent to specific disorders(5,20). As the SCID-5-PD treats the criteria for personality disorders as discrete entities of equal diagnostic importance, it can be challenging for the clinician to grasp the overall clinical picture in the absence of a more comprehensive psychiatric assessment(3,7,21). Most diagnostic criteria are, in themselves, not specific for any disorder(22): The diagnostic specificity emerges from the interaction between the symptoms and signs of the disorder. The meaningful unit of parts that emerges is called the Gestalt. Multiple interwoven sources add to the Gestalt such as the patient’s history, the context, the relation to other experiences, the form and content of the experience(23,24). In the diagnostic process there are reciprocal dependencies between the whole and its single features. When the unifying Gestalt is not engaged, these single features may appear as a conglomerate of different disease entities, creating the co-morbidity that characterizes a structured, polythetic diagnostic approach(25). According to Jaspers, the specificity of mental disorders is not graspable at the level of singular symptoms and signs, but only at the level of the Gestalt(6). Grasping the Gestalt may be particularly challenging when differentiating personality disorder from SSD, an endeavour for which a fully structured interview may not suffice.