A prospective study was carried out in order to provide an answer to the following questions. (1) Is
lithium effective as a prophylactic agent in broadly defined
schizoaffective disorders? (2) Taking for granted that
schizoaffective disorders represent a heterogeneous group of conditions, in which schizoaffective patients is
lithium effective? (3) Are there any clinical, historical or
biological predictors of response to
lithium prophylaxis in schizoaffective patients? (4) What are the minimum plasma
lithium levels required for effective prophylaxis in
schizoaffective disorders? The study confirmed the efficacy of
lithium prophylaxis in broadly defined
schizoaffective disorders, but showed that this treatment is relatively ineffective in schizoaffective patients with a prominent schizophrenic-like component in their clinical picture and in those diagnosed cross-sectionally as schizodepressive. The only successful predictor of response was a previous bipolar course of the illness (which was associated with a positive outcome of prophylaxis). Plasma
lithium levels in the range of 0.45-0.60 mEq/l did not prove to be useful for prophylactic purposes in
schizoaffective disorders.