Adult attention deficit hyperactivity symptoms and psychosis: Epidemiological evidence from a population survey in England
Introduction
Attention deficit hyperactivity disorder (ADHD) and schizophrenia have both been conceptualised as neurodevelopmental disorders (Owen et al., 2011). The defining symptoms of ADHD comprise inattention, hyperactivity and impulsivity, and are essentially neurodevelopmental arising in early childhood. There is significant persistence of symptoms from childhood to adulthood, with consequential social impairment (Barkley et al., 2002). In schizophrenia the defining symptoms of delusions, hallucinations and thought disorders commonly emerge in youth and in some patients are associated with neurocognitive and developmental deficits that precede these psychotic symptoms (Howes and Murray 2014). Given that neurocognitive features define the syndrome in ADHD, but are ancillary in psychosis, the question of the association between the two syndromes is empirical rather than definitional, and may have implications for the nature of both conditions and for mechanisms of symptom production.
So far, evidence for such an association has been sparse, inconsistent and tangential. Ross et al. (2006) reported that ADHD was the commonest comorbid condition in children and adolescents with schizophrenia. Young relatives of patients with schizophrenia have an increased rate of impulsivity, hyperactivity, attentional problems and emotional lability (Keshavan et al., 2003). Prospective studies of children with ADHD assessing the appearance of psychosis in adulthood are few in number and have led to mixed results. In a 10 year follow- up of 140 children diagnosed with ADHD, there was a trend level (p=0.057) increase in the hazard of developing psychosis (Biederman et al., 2006). Weiss et al. (1985) found no increased risk of psychosis in adulthood after 15 years in a small group of hyperactive children. Most recently however, analysis of follow-up data from the Danish Psychiatric Register of over 200 children with ADHD suggests an increased relative risk (RR: 4.3) of schizophrenia in adulthood (Dalsgaard et al., 2013).
There is a degree of overlap in the putative neuropsychological deficits in the two disorders. Attention deficits, which are part of the ADHD syndrome, are frequently identified in people with schizophrenia (Keshavan et al., 2003). Whilst neuropsychological deficits are generally associated with negative symptoms of schizophrenia, ability to sustain and select attention have also been strongly associated with positive schizotypal symptoms (Keefe et al., 1997) and positive symptoms in schizophrenia (Berman et al., 1997). Impulsivity in ADHD is thought to manifest at the motor level through hyperactivity (Rubia, 2002). Much less is known about impulsivity in schizophrenia, though it is associated with comorbid substance use and aggression (Hoptman et al., 2010).
It is possible that links between ADHD and psychosis might be drug-related effects, whether through prescription or abuse. Psychostimulant use for ADHD in children can lead to visual or tactile hallucinations (Mosholder et al., 2009). The abuse of methylphenidate is known to cause psychotic-like symptoms in adults (Morton and Stockton, 2000), an affect related to short term or chronic toxicity. Atomoxetine, the noradrenaline reuptake inhibitor prescribed for ADHD has been linked with paranoid delusions and mania-like states (Ross, 2006), albeit rarely. In those with a pre-existing diagnosis of schizophrenia, the use of methylphenidate has been shown to worsen the condition (Ekinci and Sabuncuoglu, 2011). People with ADHD are also more likely to consume illicit drugs known to increase the risk of psychosis, including cannabis (Faraone et al., 2007) and psycho-stimulants (McGough et al., 2005).
An alternative pathway between ADHD symptoms and psychosis might be provided by dysphoric mood. Anxiety and depression are strongly comorbid with ADHD (Kessler et al., 2006) occurring in 40–50% of adults with the condition, and may worsen the symptoms of ADHD (Schatz and Rostain, 2006). Anxiety and depression have also been highlighted as significant factors in cognitive models of psychosis (Garety et al., 2001). They are associated with clinical and non-clinical paranoid thinking, and, alongside mood instability, with the emergence and persistence of psychosis (Freeman et al., 2013, Marwaha et al., 2014). Dysphoric mood may thus provide a mechanism common to both adult ADHD and psychosis. If so, the aetiology of affective disturbance may also be shared by both ADHD and psychosis, and this would include childhood adversities. Alternatively, the dysphoric or social consequences of one condition might drive the emergence of the other.
We used data from the Adult Psychiatric Morbidity Survey (APMS) 2007, a household survey conducted in England, to examine the relationship between ADHD symptoms and psychosis. We tested two hypotheses: (1) adult ADHD symptoms will be associated with psychotic disorder, paranoid ideation and auditory hallucinations; (2) the association between ADHD symptoms and psychosis will be significantly mediated by prescribed ADHD medications, use of illicit drugs, and dysphoric mood.
Section snippets
Setting and design
Full details of the survey methods are available in the survey report (McManus et al., 2009). In brief, the sampling frame was the English Small Area Postcode Address File, and adults living in private households were selected using population-based multi-phase probability sampling. Experienced survey interviewers identified private households containing at least one person. They used the Kish grid method to select at random one person in each household, ensuring that all eligible household
Results
The response rate of the survey was 57%, and the age range of the 7403 respondents 16–95 years. The spread of ADHD symptoms was: 0 (38.43%), 1 (25.83%), 2 (17.46%), 3 (10.06%), 4 (5.36%), 5 (2.30%) and 6 (0.57%). The rates of each individual ADHD symptom are displayed in Table 1. There were 39 cases of people who scored 6 on the ASRS giving a prevalence of 0.53% for adult ADHD in this household survey. Other surveys have found prevalence rates of 2.9% (Faraone and Biederman, 2005) and 4.4% (
Main findings
We tested hypotheses regarding the association between the extent of ADHD symptoms, probable adult ADHD and psychosis, and examined potential underlying mechanisms. The main findings were that higher levels of ADHD symptoms in adults were associated with psychosis, paranoid ideation and auditory hallucinations. Probable ADHD caseness (ASRS=6) is associated with probable psychosis only. This persisted even when we controlled for the confounding effects of IQ, childhood conduct problems, features
Conflict of interest
S.M. has acted as an investigator in research commercially funded by Roche and Janssen-Cilag International. The other authors do not have any conflicts of interest to declare, financial or otherwise.
Financial acknowledgement
A Medical Research Council (Grant number G0902308) Senior Clinical Fellowship supports D.F. P.B. is emeritus; their respective universities or NHS Trusts employ the other authors.
Acknowledgements
We would like to acknowledge the UK Data Archive and the National Centre for Social Research as the data collectors and depositors of the study. The National Centre for Social Research and the University of Leicester were the Principal Investigators of the Adult Psychiatric Morbidity Survey. They bear no responsibility for this further analysis or interpretation of this public dataset.
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