He hypothesised that patients were distributed along a spectrum and that the person could be on a different point on the spectrum at different times. The individual was characterised as either being predominantly schizophrenic or predominantly bipolar. Originally both bipolar and unipolar concepts were used to describe patients with an illness course of recurrent episodes characterised by clear functional impairment. Confusingly, unipolar disorder has also been used to describe depressed patients without a history of mania or hypomania. Generally Bipolar-I patients are characterised with a history of mania severe enough to warrant treatment.
Psychosis is frequently evident in manic episodes.
Bipolar II patients experience episodes of hypomania, behaviours that are aberrant from normal behaviour but not acute enough to require hospitalisation. Evidence has also found an overlap in family history between both forms of the disorder that further supports the belief that both are part of the same continuum. The classifications of the milder forms of bipolar-II disorder have been inconsistent. Other studies have used alternative taxonomy in classifying different subtypes of bipolar-II patients that only confuses matters further. The 'dm' group illustrated in diagram 1 characterises patients who alternate between mild forms of depression and mild forms of mania.