Substance use linked to diagnostic instability in psychosis

By Laura Cowen, medwireNews Reporter

Comorbid substance use increases diagnostic uncertainty in patients admitted to hospital with psychosis, Australian research shows.

The effect is dependent on the type of substance abuse, with cannabis use increasing the likelihood of progression from an initial diagnosis of affective, brief, atypical or drug-induced psychosis to schizophrenia, and stimulant use reducing this likelihood, Grant Sara (Macquarie Hospital, North Ryde) and colleagues report.

Of 24,306 individuals admitted to a New South Wales public hospital between 2000 and 2011 with psychosis, 11,228 (46%) were initially diagnosed with schizophrenia, 5923 (24%) with affective psychoses or bipolar disorder and 7155 (29%) with other (brief, atypical or drug-induced) psychoses.

Between 2 and 5 years later, 82% of patients initially diagnosed with schizophrenia retained that diagnosis. By contrast, only 18% of patients with an index diagnosis of brief, atypical, or drug-induced psychosis retained their initial diagnosis. Nearly half (46%) of these patients had their diagnosis later revised to schizophrenia.

Approximately one-third of patients had at least one substance use disorder diagnosed during the study period and the researchers found that this was associated with reduced diagnostic stability. Indeed, index and final diagnoses agreed in 60% of patients without substance use disorders compared with 47% of those with substance use disorders.

Furthermore, diagnostic stability was lower for patients with stimulant use disorders than for those with cannabis use disorders, with 40% and 47% agreement between index and final diagnoses in these two groups, respectively.

When the researchers looked at predictors of diagnostic change to or from schizophrenia, they found that substance use disorders overall were not associated with a change to schizophrenia from affective or other psychoses, but were associated with a 55% increased likelihood of a change from schizophrenia to other diagnoses.

When substance use disorders were examined separately, cannabis use disorder increased the likelihood of a diagnostic change to schizophrenia by 12%, whereas stimulant use disorder decreased the likelihood by 19%.

Corresponding with this finding, Sara and team found that stimulant use disorder had the greatest effect on the change from schizophrenia to other diagnoses, more than doubling the likelihood (odds ratio 2.21), whereas cannabis use disorder had the least effect (odds ratio 1.30).

“While many people with initial diagnoses of brief and affective psychoses may progress to a diagnosis of schizophrenia, it is important to avoid premature closure on a diagnosis of schizophrenia, particularly when stimulant disorders are present”, the researchers conclude in TheJournal of Clinical Psychiatry.

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