Focal-to-bilateral tonic-clonic seizures, also known as secondary generalized tonic-clonic seizures, are a type of epileptic seizure that begins in a focal or partial area of the brain and then spreads to involve both hemispheres of the brain, leading to a tonic-clonic seizure involving the entire body.

Here's how these seizures typically progress:

Focal Onset: The seizure begins in a specific area of the brain, often referred to as the seizure focus. The initial symptoms and manifestations of the seizure are related to the function of that specific brain region. These symptoms can vary widely depending on the location of the focus and may include unusual sensations, motor movements, autonomic symptoms, or altered consciousness. The person may or may not be aware of these initial symptoms.

Spread: Over time, the abnormal electrical activity can spread from the focal area to involve both hemispheres of the brain. This transition from focal onset to generalized activity is what characterizes focal-to-bilateral tonic-clonic seizures. The person may lose awareness or consciousness during this phase.

Tonic Phase: As the seizure spreads, the tonic phase begins. During this phase, the person experiences stiffening and rigidity of the muscles. They may fall if they are standing or experience other motor manifestations.

Clonic Phase: Following the tonic phase, the seizure enters the clonic phase. In this phase, the person experiences repetitive, rhythmic, and jerking movements. This is the phase that is commonly associated with a generalized tonic-clonic seizure.

Postictal Phase: After the clonic phase, the seizure subsides, and the person enters the postictal phase. During this phase, the individual may be confused, tired, and disoriented. They may not recall the seizure or events leading up to it.

It's important to note that not all focal seizures progress to generalized tonic-clonic seizures. The progression depends on various factors, including the location and extent of the seizure focus and individual characteristics.

The treatment and management of focal-to-bilateral tonic-clonic seizures often involve antiepileptic medications to prevent or reduce the frequency of seizures. In some cases, surgical intervention may be considered to remove or disconnect the seizure focus. Managing these seizures typically requires a personalized approach, and medical professionals work closely with individuals to develop a suitable treatment plan.