A generalized tonic seizure involves bilaterally increased tone of the limbs typically lasting 3 seconds to 2 minutes. They often occur out of sleep and in runs of varying intensity of tonic stiffening. The individual is unaware during these events. At the beginning of tonic seizures with more intense stiffening, individuals may make an expiratory sound. More severe and prolonged tonic seizures may have a vibratory component which may be confused with clonic jerking. Tonic seizures often occur in individuals with intellectual impairment.
CAUTION Although asymmetry, such as head and eye deviation, can occur in a generalized tonic seizure, if consistent focal features are seen from seizure to seizure consider a focal to bilateral tonic-clonic seizure or a focal bilateral motor seizure.
NOTE Tonic seizures are one type of seizure that can result in a "drop attack", other causes of drop attacks include myoclonic (especially in younger children), atonic and myoclonic-atonic seizures.