Epilepsy and bipolar disorder share similarities and medication effectiveness, but it’s unclear if one causes the other. Antiepileptic drugs like lamotrigine, carbamazepine, and valproic acid are useful substitutes for lithium in bipolar treatment. The connection may be due to the drugs’ effects on neurotransmitter levels and the episodic nature of both diseases. The high incidence of mental health disorders in people with epilepsy suggests a link in closely related brain areas.
The connections between epilepsy and bipolar disorder continue to be made. At present, there isn’t enough information to say that one condition causes the other, but there are some notable similarities and suggestions in the medical literature that a greater understanding of these two diseases could aid in the treatment of either or both. Some of the known links between epilepsy and bipolar include that the same medications often treat them effectively, both have similar patterns of disease expression, and according to some studies, 10-12% of people with epilepsy have bipolar disorder.
Lithium is a drug primarily used to treat bipolar disorder and was investigated for use in the treatment of seizure disorders in the mid-19th century. Large doses proved effective, but the development of antiepileptic and other drugs were soon seen as far better substitutes. In the 19th century, the matter was researched in reverse and several commonly used antiepileptic drugs for epilepsy were found to be effective in treating bipolar disorder. While many of these are still off-label medications for bipolar disorder, the drugs lamotrigine (Lamictal®), carbamazepine (Tegretol®), and valproic acid (Depakote®) have proven to be very useful substitutes for lithium, with action demonstrated in the bipolar patient.
The question about epilepsy and bipolar disorder in relation to anticonvulsants is whether the two diseases are related because some of the same drugs can treat both diseases. It’s true that when epilepsy and bipolar disorder are comorbid, doctors may be able to treat both conditions with a single drug. How far the connection goes is unclear, however.
Some suggest that these specific antiepileptic drugs work because of the way they work on neurotransmitter levels in the brain. These drugs target the neurotransmitters GABA and glutamate (from which GABA is made), and glutamate in high amounts is associated with the expression of bipolar disorder and epilepsy. If the drugs that treat them do not relate the two conditions, they may be related because both diseases express dysfunctions of GABA and glutamate levels.
Another way to look at this issue is to examine how epilepsy and bipolar are expressed. Both diseases have a feature called kindling, whereby more early-onset episodes tend to predict how severe the disease will be later in life. Furthermore, both diseases tend to occur in episodes, with periods where they do not occur, and it is unclear how this episodic nature is relevant, except that it occurs in both conditions.
There are certainly 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 are high incidences of most mental health disorders in people with epilepsy. Anxiety and depressive illnesses are also extremely common. Perhaps, ultimately, 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 can also impact the functions that create the other.
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