Duration of untreated illness in psychosis: conceptualising duration of the psychosis prodrome and duration of untreated psychosis in predicting outcome and refining early intervention

Within duration of untreated illness (DUI), longer duration of untreated psychosis (DUP) is reliably associated with greater impairment. Though influential in early intervention models, conceptual challenges endure: (i) Is longer duration of the psychosis prodrome (DPP), to include its early component preceding clinical high risk for psychosis (CHR-P), also associated with greater impairment? (ii) Do DPP and DUP constitute two independent processes or successive moieties of a common process within DUI (= DPP + DUP)? This review first describes the origins of these concepts, outlines the challenges and evaluates lead-time bias as a potentially fatal artefact in the association between DUP and outcome. Then, with DPP and DUP showing similar numerical characteristics across psychotic diagnoses, it describes studies indicating that longer DPP, like longer DUP, predicts greater severity of negative symptoms across these diagnoses. Thus, DPP and DUP appear to be not only successive moieties in quantifying DUI; they also share, at least in part, an association with the severity of this fundamental determinant of impairment, functional outcome and quality of life. On this basis, the processes underlying these associations appear to include, at least in part, dichotomisation of DUI at an imprecise threshold defined by a point of transition from DPP to DUP. While the greater non-specificity of early prodromal symptoms (i.e. pre-CHR-P) has been interpreted as favouring population-based public health measures rather than targeted interventions, recent findings relating to DPP suggest that its utility as a target for early intervention may require re-evaluation. • Untreated illness summates the psychosis prodrome and untreated psychosis • Durations of each moiety and their summation predict extent of impairment • Prodrome and psychosis are, in part, successive moieties in a common process • Early prodromal features may be under-appreciated targets for early intervention • Both targeted interventions and population-based measures are indicated