Bipolar Disorder and Schizophrenia: Distinct Illnesses or a Continuum?

Bipolar disorder continues to present complex diagnostic and therapeutic challenges. Originallyconsidered 2 separate diseases (mania and depression), bipolar disorder is now recognized to be asingle disorder characterized by different subtypes and degrees of severity. Despite the availabilityof official guidelines, such as the DSM-IV and ICD-10, diagnosis is still problematic. Traditionally,bipolar disorder has been considered a clinical entity distinct from schizophrenia, although that assumptionis being increasingly challenged. Proponents of a bipolar continuum theory support the conceptof an expanded psychiatric continuum ranging from unipolar to bipolar disorders all the way toschizophrenia. This notion is supported by various independent findings. Both bipolar disorder andschizophrenia demonstrate a high degree of genetic transmissibility. Some data reported in family andtwin studies suggest hereditary overlap between the 2 disorders. Gene mapping for both diseases is inits early stages, but certain susceptibility markers appear to be located on the same chromosomes. Bipolardisorder and schizophrenia also demonstrate some similarities in neurotransmitter dysfunction.As further indirect evidence of a possible association, many newer atypical antipsychotic agents approvedfor the treatment of schizophrenia are also proving useful for bipolar disorder. Ongoing researchshould aid in the understanding of bipolar disorder and foster the development of more effectivetreatment.