Cognitive deficits and levels of IQ in adolescent onset schizophrenia and other psychotic disorders

Abstract

Cognitive deficits have been found to be prevalent in early onset schizophrenia. Whether these deficits also characterise other early onset psychotic disorders to a similar degree is unclear, as very few comparative studies have been done. The primary purpose of this study was to compare the profile and severity of cognitive impairments in first-episode early onset psychotic patients who received the schizophrenia diagnosis to those diagnosed with other non-organic, non-affective psychotic disorders. The secondary purpose was to examine whether the profile of cognitive deficits, in terms of intelligence, executive functions, memory, attention and processing speed was global or specific. First-episode psychotic adolescents (N = 39) between the ages 11 and 17 years were included, 18 of whom were diagnosed with schizophrenia, and 21 with other non-organic, non-affective psychoses, using ICD-10 criteria. A healthy control group (N = 40) was included, matched on gender and age. Cognitive functions were assessed using WISC-III/R, the CANTAB battery, WCST, Trail Making B, fluency tasks, and Buschke's selective reminding task. A similar profile and level of impairment was found on measures of attention, executive functions, reaction time, and memory in the schizophrenic and psychotic adolescent groups. However, analyses of WISC-III factor profiles suggested that early onset schizophrenia patients may have more global IQ deficits than non-organic, non-affective psychoses when examined recently after illness onset. Compared to the deficits of adult schizophrenia described in the literature, the results suggest relatively spared simple reaction times in early onset patients.

Introduction

Early onset schizophrenia (EOS), defined as illness onset before age 18, is characterised by more severe clinical symptoms, neurobiological and premorbid vulnerability indicators, developmental delays, and a higher incidence of familial schizophrenia spectrum incidence than adult onset schizophrenia (Eggers and Bunk, 1997, Remschmidt, 2002, Werry et al., 1994). Numerous studies have found comprehensive cognitive deficits in adult schizophrenic patients (AOS), encompassing global deficits from early sensory and perceptual information processing to attention, verbal and spatial learning and memory, executive functions, and social cognition (Braff, 1993, Gur et al., 2001, Heinrichs and Zakzanis, 1998). While some studies have found specific deficits beyond the global level of impairment, particularly in the areas of verbal learning and memory (Saykin et al., 1991, Tamlyn et al., 1992), or executive functions (Elliott et al., 1998), others do not support differentially impaired cognitive domains (Blanchard and Neale, 1994).

The studies that have been done in EOS support the presence of a global profile of cognitive deficits, similar to that seen in AOS (Hollis, 2000a). However, some studies including either EOS or more broadly defined schizophrenia spectrum disorders have found relatively impaired or spared domains of function. Some have found aspects of attention, such as selective attention (Oie et al., 1998) and sustained attention (Oie and Rund, 1999, Ueland et al., 2004, Kravariti et al., 2003) to be relatively intact, while others have found large deficits on attentional measures (Brickman et al., 2004, Kenny et al., 1997, McClellan et al., 2004). Some have found simple reaction time and speed of cognitive processing to be relatively spared (Kravariti et al., 2003); while others have found large deficits in these domains (Kenny et al., 1997, Ueland et al., 2004). The different findings may be due to the heterogeneity of patient samples in terms of time since illness onset, chronicity, and medication status. In terms of intelligence, most studies have found average IQ levels in EOS patients ranging from 80 to 90 (approximately 1–1½ S.D. below the normative mean), which is lower than the average IQ found in adult onset patients (Asarnow et al., 1994, Banaschewski et al., 2000, Hollis, 2003, Jacobsen and Rapoport, 1998). Approximately 1/3 of EOS patients have IQ levels lower than 70, which lies in the range of mild retardation (Hollis, 2000a). Some studies have found differential profiles of intelligence in adolescent psychotic patients, with impaired performance IQ but not verbal IQ (Aylward et al., 1984, Kravariti et al., 2003, Goldberg et al., 1988), while others have found particular deficits in the Freedom from distractibility factor with relative sparing of the factor of Perceptual organisation from WISC-R (Asarnow et al., 1994). Hence, findings have not been consistent, and the profile of IQ and cognitive deficits in EOS has not been determined.

It is unclear whether cognitive deficits are more prevalent in EOS compared to early onset patients with other non-organic psychotic disorders (McClellan et al., 2004, Kumra et al., 2000). Patients with EOS have a more severe course of illness than other psychotic disorders with onset in adolescence and most of the evidence points towards a worse functional outcome (Eggers and Bunk, 1997, Werry et al., 1994), although findings are not unanimous (Eggers, 1999). In adult patients, some studies support the presence of more extensive cognitive deficits in schizophrenia compared to other schizophrenia spectrum disorders (Johnson-Selfridge and Zalewski, 2001, Salisbury et al., 1998), while others do not (Addington et al., 2003). Most studies have included affective psychotic patients, mostly bipolar patients (Seidman et al., 2002, Goldberg, 1999). In early onset patients, few comparative studies have been done, some of which have compared very early onset schizophrenia (VEOS), i.e. onset before age 13, to psychotic disorders not otherwise specified (PNOS) and found no differences in cognitive deficits (Goldberg et al., 1988, Kumra et al., 2000). McClellan et al. (2004) found no differences between VEOS, PNOS and bipolar patients, but suggested that schizophrenic patients may have more severe global and social cognitive deficits than the other groups. It is important to note that some of these patient samples included chronic and treatment-refractory patients. Whether prevalent cognitive deficits are specific to early onset schizophrenia or exist to the same extent in early onset psychosis is unclear (Kumra et al., 2000, Werry et al., 1991). The primary purpose of the present study was to compare the profile and severity of cognitive deficits recently after illness onset in EOS to early onset non-organic, non-affective psychotic disorders (NOP). The secondary purpose was to examine whether certain cognitive domains were relatively spared or particularly impaired beyond the level of global deficits.