According to the DSM-V (American Psychological Association, 2013) bipolar disorder is a mental disorder, classified as a mood disorder, which is characterized by the presence of manic and depressive episodes. There are several subcategories of the disease, each of which has a slightly different set of diagnostic criteria, including varying degrees of mania and depression. Bipolar I disorder, which is representative of the current understanding of what was described in the nineteenth century as manic depressive disorder or affective psychosis, is characterized by one or more manic episodes, which can be, but do not need to be accompanied by one or more major depressive episodes (MDEs). Bipolar II disorder is characterized by the patient having experienced at least one hypomanic episode and one MDE during their lifetime. Cyclothymic disorder is another form of bipolar which is characterized by numerous periods of hypomanic symptoms and depressive symptoms, none of which meet criteria for a hypomanic episode or an MDE. There are also forms of bipolar that can be caused by medications or substance abuse.
Bipolar Disorder as a diagnosable disease has a rather disjointed history, but following one of the oldest known treatments for the disorder is a good way of establishing the recent medical history of the disease. Lithium is the oldest treatment of bipolar disorder, and was first described in this mode (as a treatment for the manic side of bipolar disorder) by John F. J. Cade in 1949 (Cade, 1949).
During an investigation into the toxicity of urea, Cade had injected guinea pigs with 8% urea solutions made using lithium urate, and found that the toxicity of these injections was much lower than he had previously observed with studies using the urine (which contains urea) of patients with various mental disorders (mania, schizophrenia, and melancholia (depression)). He completed case studies on 10 manic patients, all of whom displayed marked improvement in, and in several cases complete recovery from, their symptoms upon treatment with either lithium carbonate or lithium citrate (some patients experienced side effects such as nausea with the lithium citrate treatment and were switched to lithium carbonate). He also did the same tests on several patients with other disorders. Six patients with schizophrenia were treated with lithium and were found to have reduced restlessness, but otherwise these patients did not improve markedly. Cade also tested the lithium treatment on three patients with chronic depression, but there was no change.
For bipolar disorder, like other mental disorders, identification and diagnosis still relies entirely on clinical observation and evaluation of symptoms by trained psychologists and psychiatrists, usually with the use of resources such as the DSM-V mentioned earlier. Symptoms are either self-reported by the patients or observed by clinicians in a psychiatric ward or similar setting. As of yet, there are no biochemical tests to determine if someone has bipolar disorder, since there is no definitive biochemical cause of the disease. However, it is common for medical examinations to be done to rule out detectible issues, such as brain abnormalities, hypo or hyperthyroidism, metabolic dysfunction, chronic disease, or infections such as syphilis or HIV, just to rule out other possibilities (Price and Marzani-Nissen, 2012)