Alexandra Voce1, Richard Burns2, David Castle3, Bianca Calabria4, Rebecca McKetin5. 1. Centre for Research on Ageing, Health and Wellbeing, Australian National University, Building 54, Mills Road, Acton, ACT 2601, Australia. Electronic address: alexandra.voce@anu.edu.au. 2. Centre for Research on Ageing, Health and Wellbeing, Australian National University, Building 54, Mills Road, Acton, ACT 2601, Australia. Electronic address: richard.burns@anu.edu.au. 3. St Vincent's Hospital, 41 Victoria Parade, Fitzroy, VIC 3065, Australia; Department of Psychiatry, University of Melbourne, Grattan St, Melbourne, VIC 3010, Australia. Electronic address: David.CASTLE@svha.org.au. 4. National Centre for Epidemiology and Population Health, Australian National University, Building 62, Mills Road, Acton, ACT, 2601, Australia; National Drug and Alcohol Research Centre, University of New South Wales, 22-32 King Street, Randwick, NSW 2031, Australia. Electronic address: bianca.calabria@anu.edu.au. 5. National Drug Research Institute, Curtin University, GPO Box 1987, Perth, WA 6845, Australia; National Drug and Alcohol Research Centre, University of New South Wales, 22-32 King Street, Randwick, NSW 2031, Australia. Electronic address: rebecca.mcketin@curtin.edu.au.
Abstract
BACKGROUND: Positive psychotic symptoms have consistently been associated with methamphetamine use but the presence of a negative symptom cluster remains unclear. We used exploratory factor analysis to examine whether a discrete negative syndrome could be delineated among methamphetamine users, and to examine the clinical correlates of this syndrome. METHOD: Participants (N = 154) were people who used methamphetamine at least monthly and did not meet DSM-IV diagnostic criteria for lifetime schizophrenia. Scores on the Brief Psychiatric Rating Scale for the past month were subject to exploratory factor analysis. Latent class analysis was applied to resultant factor scores to determine whether negative and positive factors were experienced by the same participants. Past-month substance use measures were days of use for each drug type and methamphetamine dependence assessed using the Severity of Dependence Scale. RESULTS: We articulated a three-factor model including 'positive/activation symptoms' (e.g. suspiciousness, hallucinations, conceptual disorganisation, tension), 'affective symptoms' (e.g. depression, anxiety) and 'negative symptoms' (e.g. blunted affect, motor retardation). Positive-activation and affective symptoms (but not negative symptoms) were positively correlated with past month days of methamphetamine use (r = 0.16; r = 0.25) and severity of dependence (r = 0.24; r = 0.41). Negative symptoms were correlated with heroin (r = 0.24) and benzodiazepine use (r = 0.21). Latent class analysis revealed a three-class model comprising a positive-symptom class (44%, high positive-activation, low negative symptoms), a negative-symptom class (31%, low positive-activation, high negative symptoms), and a low-symptom class (38%, low on all factors). CONCLUSIONS: A negative symptom syndrome exists among people who use methamphetamine, but this appears related to polysubstance use rather than forming a part of the psychotic syndrome associated with methamphetamine use. Overlooking the role of polysubstance use on negative symptoms may conflate the profiles of methamphetamine-associated psychosis and schizophrenia.
BACKGROUND: Positive psychotic symptoms have consistently been associated with methamphetamine use but the presence of a negative symptom cluster remains unclear. We used exploratory factor analysis to examine whether a discrete negative syndrome could be delineated among methamphetamine users, and to examine the clinical correlates of this syndrome. METHOD:Participants (N = 154) were people who used methamphetamine at least monthly and did not meet DSM-IV diagnostic criteria for lifetime schizophrenia. Scores on the Brief Psychiatric Rating Scale for the past month were subject to exploratory factor analysis. Latent class analysis was applied to resultant factor scores to determine whether negative and positive factors were experienced by the same participants. Past-month substance use measures were days of use for each drug type and methamphetamine dependence assessed using the Severity of Dependence Scale. RESULTS: We articulated a three-factor model including 'positive/activation symptoms' (e.g. suspiciousness, hallucinations, conceptual disorganisation, tension), 'affective symptoms' (e.g. depression, anxiety) and 'negative symptoms' (e.g. blunted affect, motor retardation). Positive-activation and affective symptoms (but not negative symptoms) were positively correlated with past month days of methamphetamine use (r = 0.16; r = 0.25) and severity of dependence (r = 0.24; r = 0.41). Negative symptoms were correlated with heroin (r = 0.24) and benzodiazepine use (r = 0.21). Latent class analysis revealed a three-class model comprising a positive-symptom class (44%, high positive-activation, low negative symptoms), a negative-symptom class (31%, low positive-activation, high negative symptoms), and a low-symptom class (38%, low on all factors). CONCLUSIONS: A negative symptom syndrome exists among people who use methamphetamine, but this appears related to polysubstance use rather than forming a part of the psychotic syndrome associated with methamphetamine use. Overlooking the role of polysubstance use on negative symptoms may conflate the profiles of methamphetamine-associated psychosis and schizophrenia.