ABSTRACT
For much of the century since Kraepelin divided psychotic illness into dementia praecox and manic depressive insanity (later to become known as schizophrenia and bipolar disorder), there has been controversy over whether these two disorders are really distinct from each other. Although the illnesses appear clinically distinguishable in their pure forms, there are no pathognomic symptoms on which clinicians can rely to differentiate them and discriminant function analysis of clinical data has failed to find a ‘point of rarity’ between the two disorders. Many patients with schizophrenia have symptoms of depression and mania; patients with bipolar disorder can have Schneiderian ‘first rank’ symptoms of schizophrenia during illness exacerbation; and the diagnosis of ‘schizoaffective disorder’ is necessary to categorize the significant fraction (around 8%) of psychotic patients who cannot be classified into either of the major psychotic branches.
