Background: Whereas a growing body of evidence suggests that cycloid psychoses have to be separated from schizophrenic psychoses, their relations to bipolar affective disorder are less clear.
Patients and methods: In a controlled family study, we recruited 46 patients with cycloid psychosis (CP), 33 with manic-depressive illness (MDI), and 27 controls. Three hundred fifty-six of 389 living first-degree relatives were personally examined by experienced psychiatrists blinded to the diagnosis of the index proband.
Results: The relatives of CP patients showed significantly lower morbidity risk of functional psychoses than relatives of patients with MDI in Kaplan-Meier life table calculation. The morbidity risk for functional psychoses in relatives of patients with CP did not differ significantly from that in relatives of controls.
Conclusion: These results suggest that CP are etiologically different from bipolar affective psychoses and cannot be integrated into the spectrum of bipolar affective disorders. The findings provide further evidence for a nosological independence of CP.