Bipolar Disorder
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Bipolar disorder is a relatively common and chronic brain condition that causes patients to experience unusual shifts in a persons mood, energy and ability to function. The symptoms are more severe when compared to the normal ups and downs everyone goes through as they go through episodes of mania and depression, usually with intervening periods of relative mood stability. It has a profound negative effect on interpersonal, social, family and vocational outcomes as it can result in damaged relationships, poor job or school performance. As well, it is a risk factor for suicide. However, it can be treated and people with this illness can lead full and productive lives. The exact cause of bipolar disorder has not been elucidated as there are multiple contributors to the pathoetiology of the disorder. The course of bipolar disorder is dependent on a number of factors, including severity of the illness, the age of onset, comorbid conditions, frequency of episodes, cycle pattern and the presence or absense of rapid cycling. Other factors that can influence the course of bipolar disorder include stress, lifestyle, the sleep-wake schedule, the use of substances and alcohol and the long-term use of precription medication. Several areas of the brain have been implicated adn have focused attention towards abnormalities in the intra-cellular processes of brain function, such as cell receptors and neurotransmitter effects. The possibility of neural degeneration has also been explored as a potential common final pathway in the disorder. In addition, there is increasing evidence for a genetic component causing bipolar disorder, provided by a number of twin studies and gene linkage studies.
Approximately sixty percent of people with bipolar disorder have a substance abuse problem. Of those, forty-six percent are dependent on alcohol and the rest exhibit drug abuse or dependency. Substance abuse can make bipolar disorder more severe and worsen the course of the disease by exacerbating symptoms or precipitating episodes. The factors which may increase the risk of comobid substance abuse are family history of substance abuse, an early age of onset of bipolar disorder adn the presence of mixed episodes.
Studies have shown that the lifetime prevalence of bipolar disorder is approximately one percent. The prevalence of bipolar disorder is similar in males and in females and there appears to be no difference in prevalence rates between different racial groups. The time of onset is often in the adolescent years of young adult life, with depressive episodes usually proceeding the onset of the first manic epidode. The classic form of the disorder, Bipolar I, is characterized by manic and depressive episodes. It is equally common in men and women, while Bipolar II, characterized by hypomania and depressive episodes, is more common in women than in men. There is also evidence that women with bipolar disorder may be more prone to depressive episodes than men are.
Suicide is one of the major causes of mortality in patients with bipolar disorder, who are at a higher risk of committing than those patients with other psychiatric disorders. The lifetime prevalence of suicide in bipolar patients in fifteen percent. A study showed that twenty-five to fifty percent of pateints with bipolar disorder attempt suicide at least once in their lifetime, and that the patients often showed detailed planning and a resolute intent to die. Increased risk of suicide is associated with past attempts, alcohol abuse and the length of time elapsed after hospital discharge. Women with the disorder attempt suicide two to three times more often than men, but generally they use less lethal means.
Advanced brain imaging techniques have been done to examine brain functions and structure in people with bipolar disorder using both the functional MRI and positron emission tomography. An important area of neuroimaging research focuses on identifying and characterizing networks of interconnected nerve cells in the brain, interactions among which form the basis for normal and abnormal behaviors. Abnormalties in the structure and function of certain brain circuits could underlie bipolar disorder and studies have found anatomical differences in areas such as the prefrontal cortex and hippocampus. Better understanding of the neural circuits involved in regulating mood states and genetic factors such as the cadherin gene FAT linked to bipolar disorder, may influence the development of new and better treatments and may aid in early diagnosis or even a cure.
The main brain areas involved in bipolar disorder include the frontal and temporal lobes of the forebrain, the prefrontal cortex, the basal ganglia and parts of the limbic system. The hippocampus may also play a role in bipolar disorder, as structural changes to this area of the brain have been associated with the disorder in some individuals. The cerebral cortex is involved in thought processes and it is possible that abnormalties in this part of the forebrain are responsible for the negative thoughts that are associated with the depressive episodes of bipolar disorder.
Structural imaging studies have demonstrated a neuroanatomical basis to bipolar disorder and a reduction in overall brain volume. Specifically, an enlargement of the third and lateral ventricles and a reduction in the volume of grey matter in parts of the medial and orbital prefrontal cortices, ventral striatum and mesoisoetmporal cortex. The metabolic rate and blood flow to these areas are also disrupted in depression. The reduced brain volume is partly due to a reduction in the number of neurons and glial cells in layers II and III in the forebrain of depressed patients. These two layers have been demonstrated to be important in bipolar disorder.
Neurotransmitters are involved in the aetiology of mood disorders, especially the monoamines and acetylcholine. Earlier theories suggested an excess of neurotransmitters occured during depression. Instread, it is the effectiveness of the cell functioning under the modification and control of neurotransmitters that underlies the pathoetiology of mood disorders. Researchers know there is a link between neurotransmitters and mood disorders because drugs which alter these transmitters releive mood disorders as well. Studies suggest that a low or high level of a specific neurotransmitter such as serotonin, norepinephrine or dopamine is the cause. Another study indicates that an imbalance of these substances is the problem and that a specific level of a neurotransmitter is not as important as its amount in relation to the other neurotransmitters. And yet another study has found evidence to support a change in the sensitivity of the receptors on nerve cells that may be the issue. In conclusion, researchers can be sure that neurotransmitters are the cause of bipolar disorder just not sure of its exact role.