Problems in the boundaries of bipolar disorders.

Classical concepts of bipolarity (bipolar I and bipolar II) have sometimes been extended into a broader spectrum that includes a wide variety of conditions previously diagnosed as separate forms of psychopathology. Differential diagnosis remains important, particularly in personality disorders characterized by affective instability, and in behavior disorders affecting pre-pubertal children. In the absence of biological markers or other external sources of validity, as well as lack of evidence for response to pharmacological treatment when disorders are defined more broadly, the bipolar spectrum remains an unproven hypothesis.