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Published on: June 20, 2012
Altered Gray Matter Myelin in Type IIb Focal Cortical Dysplasia
Laura Rossini1, Emanuela Maderna1, Dalia De Santis1
1From the Epilepsy Unit (L.R., D.D.S., C.P., R.G., M.d.C.), Division of Neurology V and Neuropathology (E.M.), and Neurosurgery Unit (M.R.), Fondazione IRCCS Istituto Neurologico Carlo Besta; and Claudio Munari Epilepsy Surgery Centre (L.T.), Niguarda Hospital, Milano, Italy.
Background And Objectives:
Myelin is altered in several neurologic disorders. Published data demonstrate reduced white matter myelin content and lower oligodendrocyte cell number in postsurgical brain specimens obtained from patients with focal cortical dysplasia (FCD) and temporal lobe epilepsy; a pathogenic role of dysfunctional myelin in focal epilepsies has been proposed. Based on this evidence, our study aims to investigate the myelination status in the gray matter in postsurgical brain specimens from patients with FCDIIb.
Methods:
We collected specimens from patients with a histopathologic diagnosis of FCDIIb who underwent surgery between 1995 and 2022 in 2 epilepsy surgery centers in Milano; we used nonlesional samples and perilesional tissue within the same FCDIIb specimen as controls. Immunohistochemistry for myelin basic protein (MBP) and electron microscopy were used to quantify myelin alterations in the lesional core of FCDIIb specimens compared with nonlesional and perilesional control areas. Olig2 and breast carcinoma amplified sequence 1 immunohistochemistry, markers of oligodendrocytes, were also evaluated.
Results:
Sixteen patients with FCDIIb (24 ± 14 mean years at surgery, 44% female) and 4 controls (3 histopathology-negative epileptic patients and 1 patient with nonepileptic tumor; 32 ± 11 mean years at surgery, 50% female) were included. The cortical myeloarchitecture was disorganized in the FCD core lesion. MBP immunostained fiber density from 11 paired samples that included both the FCD lesional core and adjacent perilesional cortex in the same tissue section did not reveal a significant difference. Ultrastructural examination performed in the gray matter of 6 specimens from FCDIIb patients (both in the core and in the adjacent perilesional areas) and 2 controls revealed that exclusively in the FCDIIb core, myelinated fiber density was reduced and axons featured thin or no myelin coating and pathologic vacuoles. These changes were associated with a reduction of Olig2-immunostained cells in the FCDIIb cortex core.
Discussion:
Our findings demonstrate that the gray matter at the core of postsurgical FCDIIb specimens contains a high number of poorly myelinated axons and less oligodendrocytes; these findings suggest a potential contribution of altered myelination in the pathogenesis of FCDIIb.
Insights
Myelin is altered in focal cortical dysplasia type IIb (FCDIIb) gray matter, with reduced myelination and fewer oligodendrocytes found in surgical specimens, suggesting a role in epilepsy pathogenesis.
Area of Science:
- Neuroscience
- Neuropathology
- Epileptology
Background:
- Myelin alterations are implicated in various neurological disorders.
- Previous studies show reduced white matter myelin and oligodendrocytes in FCD and temporal lobe epilepsy.
- Dysfunctional myelin is hypothesized to contribute to focal epilepsies.
Purpose of the Study:
- To investigate the myelination status within the gray matter of postsurgical FCDIIb specimens.
- To compare myelination in the FCDIIb core lesion with surrounding nonlesional and perilesional tissues.
Main Methods:
- Analysis of postsurgical brain specimens from FCDIIb patients and controls.
- Immunohistochemistry for myelin basic protein (MBP) and Olig2.
- Electron microscopy to assess myelin and axon integrity.
- Comparison of lesional core with nonlesional and perilesional control areas.
Main Results:
- Cortical myeloarchitecture was disorganized in the FCDIIb core.
- No significant difference in MBP-stained fiber density between FCDIIb core and perilesional cortex.
- Ultrastructural analysis revealed reduced myelinated fiber density and poorly myelinated axons in the FCDIIb core.
- Fewer Olig2-positive cells were observed in the FCDIIb core.
Conclusions:
- FCDIIb gray matter core exhibits poorly myelinated axons and reduced oligodendrocyte numbers.
- These findings suggest that altered myelination may play a role in the pathogenesis of FCDIIb.
- The study highlights potential myelin defects in the gray matter of FCDIIb epilepsy.
