Predictive validity of a culturally informed diagnosis of schizophrenia: a 30 month follow-up study with first episode psychosis

Previous research has shown discrepancies between a standard diagnostic interview for schizophrenia (CASH) and a culture sensitive version of this instrument (CASH-CS) in Moroccan patients. More specifically we showed that among Moroccan immigrants the CASH-CS resulted in fewer patients with a diagnosis of schizophrenia compared with diagnoses based on the CASH, whereas for Native Dutch patients there was no difference between the CASH and the CASH-CS. The aim of the current study was to compare the predictive validity of a diagnosis of schizophrenia according to the CASH and CASH-CS.

Method: Thirty months after referral, 26 Moroccan and 26 native Dutch patients with a suspected first psychotic episode were compared with regard to 30-month diagnostic stability, symptom development, psychosocial functioning, medication use and hospitalization using baseline diagnoses based on the two versions of the CASH.

Results: Moroccan patients who were diagnosed with schizophrenia using the standard CASH at baseline had a significantly better 30-month prognosis than native Dutch patients with the same CASH diagnosis. Prognosis of schizophrenia according to the CASH-CS was similar for Moroccans and native Dutch patients. Diagnostic stability according to the CASH was high for native Dutch (92%), but low for Moroccan patients (27%), whereas diagnostic stability according to the CASH-CS was high for both groups (85% and 81%, respectively).

Conclusion: These data raise questions regarding the validity of the standard CASH in Moroccan immigrants in The Netherlands and support the validity of the CASH-CS. As a consequence, there are serious doubts about the validity of previous studies showing an increased incidence of schizophrenia in immigrants using standard diagnostic procedures.