What is a key differentiator between Bipolar I and Bipolar II disorder in terms of symptoms?

The presence of hypomania is indeed a key differentiator between Bipolar I and Bipolar II disorder. In Bipolar I disorder, an individual experiences at least one manic episode, which is characterized by a distinctly elevated or irritable mood, increased energy, and activity levels that can lead to significant impairment in functioning or require hospitalization. In contrast, Bipolar II disorder is marked by the occurrence of at least one major depressive episode and at least one hypomanic episode, but does not include full manic episodes.

Hypomania is a milder form of mania and does not typically cause the same level of impairment as a manic episode. Therefore, the distinction lies in the presence of hypomania in Bipolar II disorder compared to the manic episodes seen in Bipolar I disorder. This understanding is crucial as it influences treatment approaches and understanding the potential for mood fluctuations in individuals living with these disorders.

The other options do not effectively serve to differentiate between the two types of bipolar disorder. Severe depression can be present in both types, grandiosity can occur during manic or hypomanic episodes, and the duration of depression varies among individuals with either disorder without being a defining feature.