A range of scientific studies, most conducted in the past few decades, suggest that there is a strong connection between epilepsy and depression. The bulk of evidence for this connection concerns the empirical correlation between the two conditions. People with depression are much more likely to develop epilepsy, and people with epilepsy are much more likely to become depressed.
Evidence of a correlation between these conditions is fairly conclusive. A 2004 study published in Neurology found that the depression rate in epileptics appears to be about three times higher than the rate for people with other chronic diseases. It also found that depression often goes untreated in epileptics, partly because it presents differently than in typical cases. For example, it seems that depressed epileptics often experience irritability and anxiety. The suicide rate for people with epilepsy is—according to some estimates—ten times higher than the rate for the normal population.
The existence of a biological connection between epilepsy and depression is theorized but not well understood. Some scientists have suggested broadly that deficiencies in the neurotransmitters dopamine, serotonin, norepinephrine, and GABA can be responsible for both these diseases. Genetic connections have also been hypothesized. There is little experimental evidence, however, to support or describe more precisely a linkage of this kind.
Awareness of the connection between epilepsy and depression has grown slowly. Contemporary observers say that depression in epileptics has been ignored for a long time. They suggest that this oversight was due to a belief that the symptoms of depression were a reasonable, predictable, and non-pathological response to the suffering associated with epilepsy. Attempts to counteract this belief include a 2003 study published in Epilepsy Currents finding that the connection between epilepsy and depression does not intensify with increasingly severe or frequent seizures.
The existence of depression in people with epilepsy has implications for treatment and quality of life. Several studies have suggested that, in the case of intractable epilepsy, that which cannot be completely controlled, reducing depression should be a more important goal than reducing seizure frequency. That is, if some number of seizures are inevitable, quality of life improves more when caretakers focus on treating depression. The use of antidepressants for people with epilepsy is not well studied. Some scientists believe that antidepressants, and especially selective serotonin re-uptake inhibitors (SSRIs), increase the likelihood of seizures, but this claim is controversial.