The cause is usually as follows: In adults: A structural lesion (eg, stroke) In children: A focal cerebral cortical inflammatory process (eg, Rasmussen encephalitis), possibly caused by a chronic viral infection or by autoimmune processes Pearls & Pitfalls Consider focal-onset seizures in patients with transient, unexplained, recurrent abnormalities that appear psychiatric (eg, hallucinations, complex behavioral automatisms, speech arrest, reduced responsiveness while staring).