Dramatic Onset of Focal Seizures: Differentiating Structural Focal Epilepsy from Ring Chromosome 20

Background/Purpose: A sudden onset of epilepsy with a high number of focal seizures and deteriorating cognitive function can be caused by a focal cortical dysplasia (FCD). A diagnostic and therapeutic dilemma results if MRI does not reveal an epileptogenic lesion.

Methods: We describe the clinical course in three patients with ring chromosome 20, who presented with an epilepsy onset with a dramatic situation of focal seizures and cognitive decline after an uneventful early development. We contrast these cases with three other patients with ring chromosome 20 and with patients with a FCD in the frontal lobe.

Results: The time to diagnosis of ring chromosome 20 was longer and the number of unrevealing studies was higher in the three patients with initial focal seizures compared with those patients, who presented with nonconvulsive status epilepticus. Patients with frontal lobe epilepsy due to a FCD could be clearly identified by video EEG in association with MRI, if this was done with the high sensitivity for epilepsy-associated lesions in an epilepsy surgery program. Ring chromosome 20 was confirmed in all three patients by chromosome analysis, whereas other etiologic studies had shown normal or—in retrospect—unspecific results.

Conclusion: A group of patients with ring chromosome 20 does not present initially with the typical clinical situation of nonconvulsive status epilepticus. A comprehensive description of the spectrum of the early clinical presentations in patients with ring 20 is still lacking. The diagnosis of a ring 20 is rapid and inexpensive and should be considered early.