Diagnostic boundaries between schizophrenia and bipolar disorders: Implications for pharmacologic intervention

Schizophrenia and bipolar disorders share some genetic risk factors and are similar in several epidemiologic features. Some data in family and twin studies suggest hereditary overlap between the two disorders. Despite the availability of official diagnostic criteria, the diagnosis of bipolar disorder is still problematic. Both nosologic entities describe psychotic disorders, have similar ages at onset and are lifelong conditions. A bipolar continuum theory supports the concept of a psychiatric continuum from unipolar to bipolar disorder and scizophrenia. The diagnosis of schizoaffective disorder, which falls between schizophrenia and bipolar disorders provides support for the continuum theory of these illnesses. However, there are clear clinical distinctions between these two nosological categories according to ICD-10 and DSM-IV and lithium therapy is effective in the majority of bipolar patients, whereas few patients with schizophrenia are helped. Regardless of whether bipolar disorders and schizophrenia are heterogenous, the most important clinical need is to find safe and effective treatments for these disorders. The similar abnormalities in neurotransmitter systems between bipolar disorders and schizophrenia may account for the efficacy of some newer atypical antipsychotics, such as olanzapine and risperidone in the treatment of patients with bipolar disorder. The antimanic effect of olanzapine and risperidone is attributed to blockade of dopamine D₂ receptors and antagonism of serotonin5-HT2A receptors. Although these atypical antipsychotics were studied and marketed for the treatment of schizoprenia are now approved for the treatment of bipolar disorder. The biological similarities between the two disorders will help us in the understanding of bipolar disorder and the development of more effective treatment strategies. In clinical practice, the diagnostic separation of bipolar disorder from schizophrenia may be difficult, but it is important because of the availability of specific and effective treatments for each entity. Misdiagnosis can result in inappropriate prolonged use of antipsychotics, ineffective treatment with mood stabilizers, treatment failure and unwanted effects, while antidepressants may be associated with rapid cycling and a switch from depression to mania.