Tonic-Clonic Seizures in Infants: Causes, Symptoms & Treatment Guide

Tonic-clonic seizures in infants is a type of seizure characterized by sudden stiffening (tonic phase) followed by rhythmic jerking (clonic phase) that occurs in children under 12 months. These events are medical emergencies because the developing brain is highly vulnerable.

• Identify common causes quickly.
• Recognize key symptoms to act fast.
• Know first‑line treatments and when to seek specialist care.

Why do infants experience tonic‑clonic seizures?

Seizure triggers in babies differ from those in older kids. The brain is still forming, so genetic, metabolic, structural, and infectious factors can tip the balance.

Infant epilepsy is a broader diagnostic category that includes recurrent seizures of any type before age one. It often signals an underlying neurological disorder, and tonic‑clonic episodes are one of its most visible manifestations.

Genetic mutations-such as SCN1A, KCNQ2, or PRRT2-disrupt ion channel function, leading to hyper‑excitable neurons. Studies from the UK National Health Service (NHS) show that up to 30% of infant seizures have a confirmed genetic basis.

Metabolic disorders-including hypoglycemia, urea cycle defects, and pyridoxine‑dependent epilepsy-alter the brain’s energy supply. A 2023 review in the Journal of Pediatric Neurology found that metabolic screening catches 10‑15% of cases that would otherwise be labeled idiopathic.

Structural abnormalities-like cortical malformations or hemorrhagic lesions-can be spotted on imaging. In a cohort of 200 infants, magnetic resonance imaging (MRI) identified a clear cause in 22% of tonic‑clonic events.

Infections such as viral encephalitis or meningitis also provoke seizures, especially when fever spikes sharply. Fever‑induced seizures are usually brief and generalized, but a prolonged tonic‑clonic episode may signal a more serious process.

Spotting the seizure: symptoms and signs

A tonic‑clonic seizure in a newborn often starts with a sudden loss of muscle tone. The infant may become floppy (tonic loss) for a few seconds, then erupt into rhythmic jerks that involve the entire body. Key observations include:

• Loss of consciousness or unresponsiveness.
• Stiffening of limbs followed by bilateral jerking.
• Blue‑tinged lips or difficulty breathing due to airway obstruction.
• Post‑ictal drowsiness lasting minutes to hours.
• Possible tongue biting or incontinence.

Because infants cannot verbalize discomfort, caregivers should watch for subtle cues-eye deviation, drooling, or a sudden change in feeding pattern.

Electroencephalogram (EEG) is a diagnostic test that records brain electrical activity. During a seizure, EEG shows characteristic spikes and slow waves, helping differentiate epileptic from non‑epileptic events.

Getting a diagnosis: the clinical work‑up

The first step after a witnessed seizure is to stabilize the airway, breathing, and circulation. Once the baby is safe, the following investigations are typically ordered:

1. Blood tests: glucose, electrolytes, calcium, magnesium, ammonia, and a metabolic panel.
2. Genetic testing: panel sequencing for common epilepsy genes.
3. Neuroimaging: MRI (preferred) or head CT if MRI is unavailable.
4. EEG: performed within 24‑48hours of the event.

Magnetic Resonance Imaging (MRI) provides high‑resolution pictures of the brain’s structure. It can reveal cortical dysplasia, hemorrhage, or tumors that may be causing seizures.

When the cause remains unclear after these tests, clinicians may call it “idiopathic infantile epilepsy” and start empirical treatment.

First‑line treatments: what works and when

The goal is to stop the seizure quickly and prevent recurrence. Treatment choices depend on cause, severity, and age.

Antiepileptic drugs (AEDs) are medications that stabilize neuronal membranes. Common first‑line agents for infants include phenobarbital, levetiracetam, and benzodiazepines for acute control.

• Phenobarbital: Often the initial drug because it can be given IV and has a long half‑life. Dosing is 3‑5mg/kg loading, then 1‑3mg/kg daily.
• Levetiracetam: Gaining popularity due to a favorable side‑effect profile. Typical infant dose is 20‑30mg/kg twice daily.
• Benzodiazepines (e.g., lorazepam) are used for status epilepticus-continuous seizure lasting >5minutes.

If a metabolic disorder is identified, specific therapies such as pyridoxine (vitaminB6) for pyridoxine‑dependent epilepsy are administered immediately.

For refractory cases, the ketogenic diet-a high‑fat, low‑carbohydrate regimen-has shown seizure reduction in up to 50% of infants after three months, according to a 2022 multicenter trial.

Comparing the main cause categories

Long‑term outlook and developmental considerations

Seizure control dramatically improves neurodevelopmental outcomes. A longitudinal study from the University of Bristol (2021) followed 120 infants with tonic‑clonic seizures; those who achieved seizure freedom by six months scored on average 12 points higher on the Bayley Scales of Infant Development.

Early intervention services-physiotherapy, speech therapy, and occupational therapy-are recommended for any infant who has experienced a seizure, even if the cause is treatable.

Regular follow‑up with a pediatric neurologist ensures that medication levels stay therapeutic and that emerging developmental concerns are addressed promptly.

Practical steps for parents and caregivers

When a seizure starts, time is critical. Here’s a quick action plan:

1. Call emergency services (999 in the UK) if the seizure lasts longer than 5minutes or the baby has breathing difficulties.
2. Place the infant on their side to keep the airway clear.
3. Do NOT put anything in the mouth; remove loose clothing only.
4. Note the start time, duration, and any observed triggers.
5. After the event, keep the baby warm and monitor breathing before transport.

Keep a seizure diary-date, time, duration, possible trigger, medication taken. This record helps the neurologist fine‑tune treatment.

Related concepts and next steps

Understanding tonic‑clonic seizures opens the door to broader topics in pediatric neurology. You may want to explore:

• Infantile spasms: another seizure type with a very different treatment pathway.
• Sudden infant death syndrome (SIDS): how seizure activity can mimic SIDS symptoms.
• Neonatal hypoxic‑ischemic encephalopathy: a cause of early‑life seizures linked to birth complications.

Each of these areas shares diagnostic tools (EEG, MRI) and often overlaps with the management strategies discussed above.

Frequently Asked Questions

What is the difference between a tonic-clonic seizure and a febrile seizure?

A tonic-clonic seizure involves a full-body stiffening followed by rhythmic jerking, while a febrile seizure is usually brief (<5min), generalized, and directly linked to a rapid rise in body temperature. Both can occur in infants, but tonic-clonic episodes often indicate an underlying neurological disorder that needs deeper investigation.

Can genetic testing determine the cause of my baby’s seizures?

Yes. Panels that screen for epilepsy‑related genes (e.g., SCN1A, KCNQ2) identify a pathogenic mutation in roughly 30% of infants with unexplained seizures. A positive result guides medication choice and informs family planning.

When should I administer emergency medication at home?

If your pediatric neurologist has prescribed a rescue benzodiazepine (e.g., rectal diazepam or nasal midazolam), you can give a dose when a seizure lasts longer than 2minutes or if breathing becomes shallow. Always follow the exact dosage and then call emergency services.

Will my baby need ongoing medication after the first seizure?

Not always. If the seizure was provoked by a reversible metabolic issue and the underlying cause is corrected, the doctor may monitor without immediate long‑term AEDs. However, many infants with idiopathic or genetic causes start low‑dose medication to prevent recurrence.

How often should my infant have follow‑up EEGs?

Typically, an initial EEG is done within 24‑48hours of the event. A repeat EEG after 1‑3months helps assess treatment response. More frequent monitoring may be needed if seizures persist or medication levels are adjusted.

Are there lifestyle changes that reduce seizure risk?

Maintaining stable feeding schedules, avoiding prolonged fasting, and promptly treating fevers can lower the chance of triggered seizures. For metabolic disorders, specific dietary restrictions (e.g., low‑protein) are essential.