Bipolar disorder

BD is a group of affective disorders characterized by depressive and manic or hypomanic episodes. The disorders include BD type I (depressive and manic episodes), BD type II (depressive and hypomanic episodes), cyclothymic disorder (hypomanic and depressive symptoms that do not meet criteria for depressive episodes), and BD not otherwise specified (depressive and hypomanic-like symptoms that do not meet the diagnostic criteria for any of the aforementioned disorders).

The pathophysiology of BD is complex and not fully understood. It is believed to be multifactorial, resulting from the interplay of genetic and environmental factors and leading to disturbances in neuronal-glial plasticity, monoaminergic signaling, inflammatory homeostasis, cellular metabolic pathways, and mitochondrial function.

The lifetime prevalence of BD globally is estimated at 0.6% for bipolar I disorder, 0.4% for bipolar II disorder, 1.4% for subthreshold BD, and 2.4% for the bipolar spectrum disorder. The weighted average prevalence of bipolar spectrum disorders in children and adolescents aged 7-21 years is estimated at 2.06%.

Risk factors for BD include genetic predisposition, with a high heritability of approximately 70%, and a shared genetic risk with other mental and medical disorders. Bipolar I has a closer genetic association with schizophrenia, while bipolar II has a closer genetic association with major depressive disorder. Environmental risk factors such as childhood maltreatment are also associated with a more complex presentation of BD. Additionally, certain single-nucleotide polymorphisms and genetic variants, such as those in the CACNA1C, NCAN, DRD4, ANK3, DAOA, COMT, and MTHFR genes, have been identified as risk factors for BD.

The clinical course of BD is characterized by recurrent episodes of depression and mania or hypomania, often starting in young adulthood. Manic and hypomanic episodes are characterized by a distinct change in mood and behavior during discrete time periods, often presenting with symptoms such as inflated self-esteem or grandiosity, decreased need for sleep, pressured speech, racing thoughts, flight of ideas, distractibility, increased goal-directed activity, and excessive involvement in activities with a high potential for painful consequences. Depressive episodes in BD are similar to major depressive episodes, characterized by symptoms such as depressed mood, markedly diminished interest or pleasure in all, or almost all, activities, significant weight loss or gain, insomnia or hypersomnia, psychomotor agitation or retardation, fatigue or loss of energy, feelings of worthlessness or excessive or inappropriate guilt, diminished ability to think or concentrate, or indecisiveness, and recurrent thoughts of death, recurrent suicidal ideation without a specific plan, or a suicide attempt or a specific plan for committing suicide.

Life expectancy in BD is reduced by approximately 10-20 potential years of life, mainly due to excess deaths from CVD and suicide.