Hjorthøj C, et al. - Researchers aimed at investigating if substance use disorders, in particular, cannabis use disorder, are associated with conversion to schizophrenia in individuals with schizotypal disorder. Findings supported the association of substance use disorders with the conversion from schizotypal disorder to schizophrenia. This was particularly observed with cannabis, amphetamines, and opioids use disorders. However, high conversion rates were evident even in those without substance use disorders, indicating that individuals with schizotypal disorder may require universal and substance-targeted prevention.

Methods

• A population-based sample of all individuals born in Denmark from January 1, 1981, through August 10, 2014, with an incident diagnosis of schizotypal disorder and without a previous diagnosis of schizophrenia was included in this prospective cohort study.
• On August 10, 2014, follow-up was completed.
• Data analysis was performed from March 10, 2017, through February 15, 2018.
• Researchers combined the information on substance use disorders from 5 different registers.
• They used Cox proportional hazards regression using time-varying information on substance use disorders and receipt of antipsychotics and adjusted for parental history of mental disorders, sex, birth year, and calendar year to determine hazard ratios (HRs) and 95% CIs for conversion to schizophrenia.

Results

• Researchers identified a total of 2,539 participants with incident schizotypal disorder (1,448 men [57.0%] and 1,091 women [43.0%]; mean [SD] age, 20.9 [4.4] years).
• Conversion to schizophrenia was noted in 16.3% (95% CI, 14.8%-17.8%) after 2 years.
• They noted conversion rate of 33.1% (95% CI, 29.3%-37.3%) overall and 58.2% (95% CI, 44.8%-72.2%) among those with cannabis use disorders after 20 years.
• Any substance use disorder was noted to be associated with conversion to schizophrenia (HR, 1.34; 95% CI, 1.11-1.63) in fully adjusted models.
• Cannabis use disorders (HR, 1.30; 95% CI, 1.01-1.68), amphetamine use disorders (HR, 1.90; 95% CI, 1.14-3.17), and opioid use disorders (HR, 2.74; 95% CI, 1.38-5.45) were identified to be linked with conversion to schizophrenia when data were stratified by substance.
• Concurrent use of antipsychotics, functional level before incident schizotypal disorder, or parental history of mental disorders did not explained these associations.