What distinguishes bipolar I disorder from bipolar II disorder?

The distinction between bipolar I disorder and bipolar II disorder primarily revolves around the type and severity of episodes experienced. In bipolar I disorder, individuals experience at least one manic episode that is sufficiently severe to cause significant impairment or necessitate hospitalization. These manic episodes are characterized by an elevated, expansive, or irritable mood, combined with increased activity or energy, and can lead to notable dysfunction in social or occupational areas of functioning.

On the other hand, bipolar II disorder involves a pattern of depressive episodes and hypomanic episodes (which are less severe than full manic episodes). Therefore, the presence of manic episodes is what specifically identifies bipolar I disorder and differentiates it from bipolar II disorder.

The other options do not correctly capture the key differences between the two disorders. For example, bipolar II disorder does not consist solely of depressive episodes; hypomanic episodes also characterize it. Additionally, psychotic symptoms are not a requisite feature for diagnosis in either type of bipolar disorder, as they can occur but are not essential criteria. Lastly, the duration of episodes can vary significantly among individuals and is not a definitive factor in distinguishing between the two disorders. Thus, the presence of manic episodes is the critical distinguishing factor for bipolar I disorder.