What is bizarre in bizarre delusions? A critical review

Diagnostic and Statistical Manual of Mental Disorder,Fourth Edition (DSM-IV) treats the presence of bizarredelusions (BD) as the heaviest-weighted clinical criterionof schizophrenia. Although BD play a major role in contemporarydiagnostic systems, only a few empirical studies explorethis issue. These studies provide highly heterogenousresults because they are based on different experimentalparadigms, in terms of definition, clinical sample, and numberof raters. Here, we first discuss the psychopathologicalsources of the concept of BD, which were initially describedas either nonsensical or incomprehensible. Then, we providea critical review of contemporary studies on the reliabilityof BD and their methodological and conceptual limitations.Current approaches have focused intensely on BD's reliabilityand have defined BD strictly in terms of delusionalcontent-mainly in terms of the physical impossibility orthe cultural or historical incomprehensibility of the delusionalclaims. These approaches have neglected formal featuresof experience that underlie BD and the crucial issue ofthe nature and validity of BD. In the discussion, we arguethat clinical diagnosis of BD cannot be limited to delusionalcontents alone and requires taking into account the subjectiveside of BD (how altered experience manifests itself) aswell as the conditions of intersubjective encounter (how BDare expressed to and experienced by the clinician). Thenotion of "bizarreness" in schizophrenia is not purely theoretical;it has practical relevance for the therapeutic encounterand implications on further empirical researchand on diagnostic approaches.