Diagnosis of the Psychoses

Abstract

The phenomenon of psychosis has inspired and intrigued clinicians and scientists for centuries, from its diagnosis to its treatment and from its molecular basis to its behavioral presentation. This chapter focuses on diagnosis. It begins with an overview of the characteristic signs and symptoms that constitute the syndrome of psychosis, as well as the historical frame in which these features came to be recognized and categorized. This text also addresses the ongoing debate about the appropriate classification of psychosis within a disease category. This deliberation has been ongoing for over a century as, despite the fact that psychosis can be diagnosed with high reliability, there is wide variability in the natural history of patients with psychosis. The major variations discussed in this section include the presence of concurrent affective symptoms, episodicity, and prognosis. Given this variability, the question arises as to whether psychosis should be split into two distinct diagnostic categories according to the degree of prominence of affective symptoms (as in Kraepelin’s dichotomy between dementia praecox and manic-depressive insanity) or whether it constitute its own diagnostic category of “the psychoses” which presents variably with other symptoms across a spectrum (the unitary theory of psychosis)? To address this controversial subject, the next section of the chapter is devoted to a historical review of the major theories on the diagnostic classification or nosology of the psychoses. It also describes and contrasts the most prominently accepted systems of classification: the Diagnostic and Statistical Manual of Mental Disorders (DSM) and the International Classification of Disease (ICD), as well as two research-based systems (the Feighner Criteria and the Research Diagnostic Criteria). The chapter concludes with a description of the frontiers of diagnostic classification which currently include the DSM5 (slated for publication in 2013) as well a novel project by the National Institute of Mental Health, called the Research Domain Criteria (RDoC) that promises to recast our conceptualization of mental illness.