Seasonal patterns of recurrence in schizophreniform psychosis

Patterns of recurrence were studied in 54 patients with a diagnosis other than affective illness, who had had 4 or more episodes, each lasting less than 6 months. Their diagnoses for the last hospitalization were: schizophrenia in 46 cases, 'catatonia' in 3 cases and atypical psychosis in 5 cases. Six patients (11%) fulfilled criteria nearly comparable to the DSM-IIIR diagnostic criteria for seasonal patterns. This prevalence is significantly higher than expected by chance and suggests that seasonal recurrence is not confined to affective illness. Four others showed an apparent periodicity shorter than 12 months, a finding which suggests that an endogenous circannual rhythm was at work in these cases and possibly also in some of the cases with an apparent seasonality of recurrence.