The Profile and Structure of Psychotic Symptoms associated with Methamphetamine Use

Abstract

Background: Methamphetamine use can precipitate a transient psychotic state, referred to as methamphetamine-associated psychosis (MAP). It can be challenging to distinguish MAP from schizophrenia (SZ) in clinical settings, as these disorders share a similar psychiatric symptom profile. The overlap between MAP and SZ has led some people to question whether MAP is better conceptualised as a distinct clinical entity, or as a precipitation of SZ. To address these issues, this thesis aimed to examine the profile and underlying structure of psychotic symptoms associated with methamphetamine use.

Methods: Four research approaches were adopted. A systematic review (study one) was conducted to canvas the existing literature for specific psychiatric symptoms, and the duration of symptoms, in MAP (k=94; n=7387). Univariate regression (study two) was used to investigate the association between methamphetamine use and psychiatric symptom prevalence in a cohort of people with primary psychosis (n=636). Exploratory factor analysis (study three) was used to investigate the factor structure of psychiatric symptoms among a cross-sectional survey of people who use methamphetamine (n=153). Latent class analysis (LCA) was used to examine profiles of lifetime psychotic symptoms among people currently using methamphetamine (n=554, study four), and the concordance between these profiles and a diagnosis of SZ was assessed. In study five, LCA was used to investigate profiles of current psychiatric symptoms among people with past-month methamphetamine use (n=160), and the alignment of these profiles with diagnoses of MAP and SZ was examined.

Results: The systematic review (study one) found that most commonly reported symptoms of MAP were persecutory delusions, auditory and visual hallucinations, hostility, and conceptual disorganisation. One-quarter of people with MAP reported persistent psychotic symptoms (>1 month after drug cessation). Methamphetamine use was associated with a higher prevalence of hallucinations and persecutory delusions among people with SZ (study two). A three-factor model of psychiatric symptoms was identified amongst people who use methamphetamine (study three), including a positive/activation factor and an affective factor (both associated with methamphetamine use), and a negative symptoms factor (associated with depressant drug use, but not methamphetamine use). Follow-up LCA showed that negative symptoms were not observed among people with positive/activation symptoms. LCA revealed three profiles of lifetime psychotic symptoms (study four), and three profiles of current psychiatric symptoms (study five) amongst methamphetamine users. In both LCA models, a class of individuals who experienced persecutory delusions and hallucinations were differentiated from a smaller class who experienced a wider range of symptoms (i.e. non persecutory delusions) and who were more likely to meet criteria for SZ.

Conclusions: Persecutory delusions, hallucinations, hostility, and conceptual disorganisation are prominent symptoms of MAP. Negative symptoms do not appear to be a component of MAP, but rather are associated with polysubstance use. Two distinct psychotic syndromes exist among people who use methamphetamine. These empirically-derived syndromes partially aligned with current diagnostic constructs, and are consistent with the need for a MAP diagnostic category separate from SZ. Greater consideration of specific symptoms (e.g., negative symptoms and non-persecutory delusions) may improve diagnostic accuracy by identifying people with a higher risk of SZ.