Connections continue to be made between epilepsy and bipolar disorder. As of yet, there is not enough information to say that one condition causes the other, but there are some similarities that are worth noting and suggestions in the medical literature that a greater understanding of these two diseases could help in the treatment of one or both. . Some of the known links between epilepsy and bipolar include the fact that the same medications often treat them effectively, both have similar disease expression patterns, and according to some studies, 10-12% of people with epilepsy have bipolar disorder.
Lithium is a drug used primarily to treat bipolar disorder and was investigated for use in treating seizure disorders in the mid-19th century. Large doses were found to be effective, but the development of anti-seizure drugs and others were soon seen as much better replacements. In the 20th century, the matter was studied in reverse, and it was discovered that several commonly used anti-seizure medications for epilepsy proved effective in treating bipolar disorder. Although many of these are still "not indicated" medications for bipolar treatment, the medications lamotrigine (Lamictal®), carbamazepine (Tegretol®), and valproic acid (Depakote®) have been found to be really useful replacements for lithium, with proven action in the bipolar patient.
The question about epilepsy and bipolar disorder as it relates to anticonvulsants is whether the two illnesses are related because some of the same medications can treat both illnesses. It's true that when epilepsy and bipolar are comorbid, doctors can treat both conditions with just one drug. It is not clear how far the connection goes.
Some suggest that these specific anti-seizure medications work because of the way they operate on neurotransmitter levels in the brain. These drugs target the neurotransmitters GABA and glutamate (from which GABA is made), and glutamate in large amounts is associated with the expression of bipolar and epilepsy. If the drugs that treat them do not link the two conditions, they may be related because both diseases express dysfunction of GABA and glutamate levels.
Another way to look at this problem is by examining how epilepsy and bipolar express themselves. Both diseases have a characteristic called on , whereby a greater number of episodes in an earlier onset tends to predict how severe the disease will be throughout life. Furthermore, both diseases tend to occur in episodes, with periods when they are not occurring, and it is unclear how this episodic nature is relevant, except that it occurs in both conditions.
Certainly, there are a significant number of people with seizures who also have bipolar disorder. The 10-12% crossover cannot be a coincidence. On the other hand, there is a high incidence of most mental health disorders in people with epilepsy. Anxiety and depressive illnesses are also extremely common. Perhaps, in the end, the main link is that these disorders occur in areas of the brain that are closely related, and what affects the functions that cause one disease may also affect the functions that create the other.