Focal seizures are usually the initial seizure type, with features referable to the hemimegalencephalic hemisphere. If these do not have motor features, they may be difficult to detect in infants.
Focal to bilateral tonic-clonic seizures can occur, these may have focal features referable to the hemimegalencephalic hemisphere if this information is carefully sought.
Epileptic spasms are seen, these may have focal features that are referable to the hemimegalencephalic hemisphere.
Status epilepticus, including focal status epilepticus, can occur.
CAUTION patients with hemimegalencephaly may have a change in their seizure types over time with the emergence of epileptic spasms or generalized seizure types, such as atypical absence, atonic and tonic seizures. Developmental and cognitive impairments are more common in this group. If these seizure types are seen, achieving full seizure control is important, if this is not achieved with medication, epilepsy surgery should be considered.