Lateralizing value of asymmetric tonic limb posturing observed in secondarily generalized tonic-clonic seizures

A striking asymmetry of limb posture occurs during secondarily generalized tonic-clonic (GTC) seizures wherein one elbow is extended while the other is flexed during the tonic phase of the GTC seizure. We have named this phenomenon asymmetric tonic limb posturing (ATLP) or the "Figure 4 Sign."

Fifty-nine secondarily GTC seizures from 31 patients with partial epilepsy who underwent successful epilepsy surgery were analyzed, in addition to another group of 64 GTC and generalized clonic seizures from 26 patients collected prospectively over a 7-month period. Three observers reviewed these seizures blinded to the side of ictal EEG onset and other clinical data.

The extended elbow was contralateral to the side of ictal onset in 35 of 39 patients who had ATLP during their seizures. The kappa index, a measure of interobserver agreement, was calculated, and ATLP was found to have very good agreement between observers.

In secondarily generalized tonic-clonic seizures, ATLP (Figure 4 Sign) may sometimes be only available lateralizing sign.