Pathological Networks Involving Dysmorphic Neurons in Type II Focal Cortical Dysplasia

Focal cortical dysplasia (FCD) is one of the most common causes of drug-resistant epilepsy. Dysmorphic neurons are the major histopathological feature of type II FCD, but their role in seizure genesis in FCD is unclear. Here we performed whole-cell patch-clamp recording and morphological reconstruction of cortical principal neurons in postsurgical brain tissue from drug-resistant epilepsy patients. Quantitative analyses revealed distinct morphological and electrophysiological characteristics of the upper layer dysmorphic neurons in type II FCD, including an enlarged soma, aberrant dendritic arbors, increased current injection for rheobase action potential firing, and reduced action potential firing frequency. Intriguingly, the upper layer dysmorphic neurons received decreased glutamatergic and increased GABAergic synaptic inputs that were coupled with upregulation of the Na+-K+-Cl- cotransporter. In addition, we found a depolarizing shift of the GABA reversal potential in the CamKII-cre::PTENflox/flox mouse model of drug-resistant epilepsy, suggesting that enhanced GABAergic inputs might depolarize dysmorphic neurons. Thus, imbalance of synaptic excitation and inhibition of dysmorphic neurons may contribute to seizure genesis in type II FCD.

A case of focal cortical dysplasia type IIa with pathologically suspected bilateral Rasmussen syndrome

BACKGROUND

Rasmussen syndrome (RS) is a rare neurological disorder characterized by unilateral chronic inflammation, drug-resistant epilepsy, and progressive neurological and cognitive deterioration. There has been no detailed pathological evaluation or finding, including focal cortical dysplasia, for bilateral RS.

CASE REPORT

A 13-year-old boy presented with status epilepticus with focal to bilateral tonic clonic seizure starting from the left upper limb. At the age of 15, epilepsia partialis continua of the right face and upper extremities appeared, and MRI showed hemispheric abnormal signal intensities with left frontal lobe predominance. Three months later, MRI showed extensive abnormal signal intensities in the right occipitoparietal and left temporal lobes. Tacrolimus was useful in preventing recurrence. Because the seizures were intractable, a corpus callosotomy was performed at 16 years along with a concurrent brain biopsy from the bilateral lateral frontal cortices. We detected dysmorphic neurons in addition to inflammatory changes suspicious for RS, leading to a diagnosis of focal cortical dysplasia (FCD) type Ⅱa and suspected bilateral RS. Total callosotomy and vagus nerve stimulation were not sufficiently effective.

CONCLUSIONS

In bilateral RS, FCD may be present in both cerebral hemispheres. In the current case, an autoimmune response to dysmorphic neurons may have contributed to the pathogenesis of intense inflammation.