Psychiatric diagnosis as prototype categorization

How doctors generate diagnostic hypotheses: a study of radiological diagnosis with functional magnetic resonance imaging

BACKGROUND

In medical practice, diagnostic hypotheses are often made by physicians in the first moments of contact with patients; sometimes even before they report their symptoms. We propose that generation of diagnostic hypotheses in this context is the result of cognitive processes subserved by brain mechanisms that are similar to those involved in naming objects or concepts in everyday life.

METHODOLOGY AND PRINCIPAL FINDINGS

To test this proposal we developed an experimental paradigm with functional magnetic resonance imaging (fMRI) using radiological diagnosis as a model. Twenty-five radiologists diagnosed lesions in chest X-ray images and named non-medical targets (animals) embedded in chest X-ray images while being scanned in a fMRI session. Images were presented for 1.5 seconds; response times (RTs) and the ensuing cortical activations were assessed. The mean response time for diagnosing lesions was 1.33 (SD ±0.14) seconds and 1.23 (SD ±0.13) seconds for naming animals. 72% of the radiologists reported cogitating differential diagnoses during trials (3.5 seconds). The overall pattern of cortical activations was remarkably similar for both types of targets. However, within the neural systems shared by both stimuli, activation was significantly greater in left inferior frontal sulcus and posterior cingulate cortex for lesions relative to animals.

CONCLUSIONS

Generation of diagnostic hypotheses and differential diagnoses made through the immediate visual recognition of clinical signs can be a fast and automatic process. The co-localization of significant brain activation for lesions and animals suggests that generating diagnostic hypotheses for lesions and naming animals are served by the same neuronal systems. Nevertheless, diagnosing lesions was cognitively more demanding and associated with more activation in higher order cortical areas. These results support the hypothesis that medical diagnoses based on prompt visual recognition of clinical signs and naming in everyday life are supported by similar brain systems.

Clinical homogeneity of DSM-IV schizophrenic disorders

We investigated the lifetime fulfillment of five subcriteria of diagnostic criterion A in 94 inpatients with a definite diagnosis of DSM-IV schizophrenic disorder. Among the five diagnostic features captured by criterion A, only delusions were found to be almost universal, whereas of the remaining four, only hallucinations and negative symptoms occurred in more than half of all the cases. Overall, almost 60% of the 28 possible patterns of combination among the five subcriteria were found to be fulfilled although 60% of the cases were accounted for by only 4 patterns, which were also identified by means of a cluster analysis, as accounting for the totality of the cases. The first cluster was characterized by the fulfillment of subcriteria 1,2 and 5, the second by subcriteria 1 and 2, the third by subcriteria 1 and 5 and the fourth by subcriteria 1,2, and 3. The substantial clinical heterogeneity of the DSM-IV category of schizophrenic disorders with respect to their diagnostically characteristic features captured in criterion A is traced to the polythetic character of its five subcriteria.

The MMPI, prototypal typology, and borderline personality disorder

This study demonstrates inherent features in the DSM-III diagnostic criteria for personality disorders (i.e., overlapping diagnoses and heterogeneous symptomatology) that limit efforts to identify a sensitive and specific MMPI profile for the borderline personality disorder. A sample of 71 inpatients was administered an MMPI and a semistructured interview that systematically evaluated each of 81 symptoms for the 11 DSM-III personality disorders. Interrater reliability was substantially higher than has been obtained with unstructured interviews. The effect on the borderline MMPI profile of variation in the number of borderline symptoms and overlap with the schizotypal, histrionic, and antisocial diagnoses was demonstrated. We discuss implications with respect to a prototypal model of classification.