MDD: Major depressive disorder (i.e. depression)
Bipolar disorder (or manic-depressive illness) is often a severe, chronic illness chracterised by periods of depression and elation. Manic and depressed phase are both associated with significant morbidity and mortality. Bipolar disorder is usually divided into two forms, I and II. The diagnosis of bipolar I disorder requires a manic episode.
A manic episode is characterized by seven features, which I remember by the mnemonic "fidgets" -
- Flight of ideas (the subject feeling that thoughts are going too fast),
- Increased goal-related activity,
- Grandiosity (thinking that one is of a great status, etc.)
- Excessive pleasurable activity,
- Sleep disturbance
The individual may also have experienced depressive episode or mixed episodes of manic and depressive symptoms in the past.
The diagnosis of a bipolar II disorder requires at least 2 prior major depressive episode and a hypomanic episode. Once an individual is diagnosed of a bipolar I or bipolar II disorder, the diagnosis during subsequent mood episodes continues to be bipolar disorder, with the most recent episode being described as depressed, hypomanic or manic.
Patients with bipolar disorders common experience several major depressive episode prior to their first manic or hypomanic episode. Early in the illness episodes of depression or mania are separated by relatively long periods of normal behavior, but without treatment subsequent episodes become increasingly frequent.
Untreated manic or depressive episodes typically last several months. Treatment results in shortening in length and decrease in severity.
Rapid cycling form of bipolar disorder affects 10-15% of the patients and is characterized by increased frequency of episodes to 2-4 times per year. This form is associated with a poor prognosis and is less responsive to treatment.
Psychotic symptoms may develop during any manic episode, but once present subsequent manic episodes are more likely to be accompanied by psychotic features. Approximately 20-30% of patients with bipolar disorder, and 15-20% of patients with bipolar II disorder (patients who experience hypomanic episodes with depressive episodes) do not experience total recovery between episodes.
Prevalence and heritability
The prevalence of bipolar disorderis about 1.5% and 3% of the general populaton. The lifetime prevalence is approximately 0.8% for bipolar I disorder, 0.5% for bipolar II disorder. The prevalence of these disorders are the same for male and female.
Bipolar disorders cluster in families. For bipolar I disorder, the risk among first degree relative is 6-7% for bipolar I disorder, 2-5% for bipolar II disorder and 25-35% for MDD. Concordance rate for the monozygotic twins is 75% for bipolar disorder and 50% for major depressive disorder, suggestive of nonheritable as well as heritable factors in disease expression.
In contrast, first degree relatives of patients suffering from bipolar II disorder is at significantly increased risk of developing bipolar II disorder and MDD but not bipolar I disorder.
Twin, adoption and family studies indicate that genetic factors substantially contribute to the liability for developing bipolar disorder and major depressive disorder. The earlier age of onset appears to be associated with increased transmissibility of both bipolar disorder and MDD.
Taken at face value, adult twin and adoption studies indicate that familial transmission of bipolar disorder is largely a result of genetic factors and that genetic factors are more important in the development of bipolar disorder than in depressive disorder.
The heritability of bipolar disorder is estimated to be 60-70% whereas that of adult MDD is about 40%.
Bipolar disorder, like MDD, carries an increased risk of suicide and accidental death. Suicide are more common during depressed or mixed manic/depressive episodes, and while intoxicated.
Accidental injury or death are more common in manic state because of poor judgement and increased risk-taking behavior. In the elderly, mania is associated with increased medical morbidity due to malnutrition and exhaustion states from increased activity and decreased sleep.
Mania, hypomania and cyclothymia are all associated with occupational, scholastic and social impairment. The risks of comorbidities such as alcoholic abuse are markedly increased.
Patients with mixed manic/depressive episode appear to have the highest psychosocial morbidity.