EEG for Landau-Kleffner / language loss age 4+

My nearly 5 year old autistic son has experienced regression in his language over the last year. As such our paediatrician has referred him for an eeg to determine whether he may have Landau-Kleffner syndrome. Has anyone else’s child been through an eeg and do you have any advice from your experience? I’m also curious whether anyone else’s child has experienced language loss at age 4+ and whether I should be pushing for any other tests to offer a possible explanation for this in addition to Landau -Kleffner? Thanks in advance!