Insulin-like growth factor 1 receptor correlates with verbal memory in ILAE type 2 hippocampal sclerosis

Long-term memory deficits are often seen in patients with temporal lobe epilepsy (TLE). Recently, studies showed that patients with hippocampal sclerosis (HS) type 2, which presents with severe neuron loss in CA1 only, performed within the normal range. However, up to 30% of HS type 2 cases have memory deficits. As insulin-like growth factor 1 (IGF-1) is related to neurogenesis and memory performance, we sought to investigate a possible link between the expression of IGF-1 receptor (IGF-1R) and verbal memory performance among patients with HS type 2.

We selected 21 patients with left-side TLE and HS type 2. Based on presurgical neuropsychological assessment, we divided the patients into a group with normal long-term verbal memory (Preserved group, n = 15) and another with memory deficit (Deficit group, n = 6). To classify the patients, we used performance on the late recall subitems in the Logical Memory test of the Wechsler Memory Scale and late recall in Rey Auditory Verbal Learning Test (RAVLT). Coronal hippocampal sections at the body level were submitted to immunohistochemistry for NeuN and IGF-1R to evaluate neuron density and IGF-1R expression, respectively.

Patients with preserved memory had the same clinical characteristics as those with memory deficit. The groups had no difference on the short-term subitem of Logical Memory or on RAVLT learning. The Deficit group had lower scores on both long-term memory subitems. Neuron density was also similar among patients in the Preserved and Deficit groups. IGF-1R expression was significantly higher in the granule cell layer and in CA2 in the Preserved group compared to the Deficit group, and IGF-1 expression had strong positive correlation with both the learning and long-term subitems of RAVLT.

Lower IGF-1 pathway activity is associated with long-term memory deficit in patients with HS type 2.