Connections between epilepsy and bipolar disorder continue to be established. As yet, there isn’t enough information to say that one condition causes the other, but there are some similarities worth noting and suggestions in the medical literature that greater understanding of these two diseases might 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 effectively treat them, 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 mainly used to treat bipolar disorder and it was investigated for use in the treatment of seizure disorders in the mid-19th century. Large doses were found effective, but the development of anti-seizure drugs and others were soon considered far better replacements. In the 20th century, the matter was studied in the reverse, and it was found that several anti-seizure drugs commonly used for epilepsy proved effective to treat bipolar disorder. Though many of these are still “off-label” drugs for bipolar, the medications lamotrigine (Lamictal®), carbamazepine (Tegretol®) and valproic acid (Depakote®) have all been found truly useful replacements for lithium, with proven action in the bipolar patient.
The question about epilepsy and bipolar disorder as they relate to anti-convulsants is whether the two diseases are related because some of the same drugs can treat both illnesses. It’s true that when epilepsy and bipolar are comorbid, doctors may be able to treat both conditions with one medication. It’s unclear how far the connection goes, however.
Some suggest that these specific anti-seizure drugs work because of the way they operate on brain neurotransmitter levels. These drugs target the neurotransmitters GABA and glutamate (from which GABA is made), and glutamate in high amounts is associated with expression of bipolar and epilepsy. If the drugs that treat them don’t relate the two conditions, they may be related because both illnesses express dysfunction of GABA and glutamate levels.
Another way of looking at this issue is by examining how epilepsy and bipolar are expressed. Both diseases have a feature called kindling, whereby a higher number of episodes at earlier onset tends to predict how severe the disease will be throughout the lifetime. Also, both illnesses tend to occur in episodes, with periods where they aren’t occurring, and it’s not clear how this episodic nature is relevant, except that it happens in both conditions.
There are certainly a significant number of people with seizures who also have bipolar disorder. 10-12% crossover cannot be coincidence. On the other hand, there are high incidences of most mental health disorders in people with epilepsy. Anxiety and depressive illnesses are extremely common too. Perhaps, in the end, the main link is these disorders happen in brain areas that are intricately related and what affects the functions causing one illness may also impact the functions that create the other.