Hippocampal sclerosis

Hippocampal sclerosis is often associated with temporal lobe epilepsy. Ammon's horn sclerosis (AHS) is the type of hippocampal sclerosis associated with mesial temporal lobe epilepsy. The terms are often used interchangeably but Ammon's horn sclerosis does not involve the dentate gyrus.[9][10][11]

The type of neuronal loss in temporal lobe epilepsy (TLE), is primarily found in the hippocampus, and can be seen in approximately 65% of TLE cases. Sclerotic hippocampus is pointed to as the most likely origin of chronic seizures in temporal lobe epilepsy, rather than the amygdala or other temporal lobe regions.[12] Although hippocampal sclerosis has been identified as a distinctive feature of the pathology associated with temporal lobe epilepsy, this disorder is not merely a consequence of prolonged seizures as argued.[12] A long and ongoing debate addresses the issue of whether hippocampal sclerosis is the cause or the consequence of chronic and pharmaceutically resistant seizure activity. Temporal lobectomy is a common treatment for TLE, surgically removing the seizure focal area, though complications can be severe.[13]

Mesial temporal lobe epilepsy (MTLE), may be due to hippocampal sclerosis,[14][11] or due to thalamic changes in temporal lobe epilepsy with and without hippocampal sclerosis,[15][11]

Although hippocampal sclerosis is relatively commonly found among elderly people (≈10% of individuals over the age of 85 years), association between this disease and aging remains unknown.[16]

There were also observations that hippocampal sclerosis was associated with vascular risk factors. Hippocampal sclerosis cases were more likely than Alzheimer's disease to have had a history of stroke (56% vs. 25%) or hypertension (56% vs. 40%), evidence of small vessel disease (25% vs. 6%), but less likely to have had diabetes mellitus (0% vs. 22%).[8]

Socioeconomic correlates of health have been well established in the study of heart disease, lung cancer, and diabetes. Many of the explanations for the increased incidence of these conditions in people with lower socioeconomic status (SES) suggest they are the result of poor diet, low levels of exercise, dangerous jobs (exposure to toxins etc.) and increased levels of smoking and alcohol intake in socially deprived populations. Hesdorffer et al. found that low SES, indexed by poor education and lack of home ownership, was a risk factor for epilepsy in adults, but not in children in a population study.[17] Low socioeconomic status may have a cumulative effect for the risk of developing epilepsy over a lifetime.[18]

Mesial temporal sclerosis is a specific pattern of hippocampal neuron cell loss.[19][20] There are three specific patterns of cell loss. Cell loss might involve sectors CA1 and CA4, CA4 alone, or CA1 to CA4.[20] Associated hippocampal atrophy and gliosis is common.[19] MRI scan commonly displays increased T2 signal and hippocampal atrophy.[19] Mesial temporal sclerosis might occur with other temporal lobe abnormalities (dual pathology).[19] Mesial temporal sclerosis is the most common pathological abnormality in temporal lobe epilepsy.[19][20] It has been linked to abnormalities in TDP-43.[21]