Atonic Seizure: Symptoms, Types, Causes and Treatment

Atonic seizures, sometimes known as "drop attacks," are a unique and often misunderstood seizure type. They are characterized by a sudden loss of muscle tone, which can lead to unexpected falls or head drops. While these seizures can be brief, their impact is significant due to the risk of injury and the challenges they pose for management. In this article, we’ll explore the key symptoms, the different types, underlying causes, and current treatment options for atonic seizures—making sense of the latest research to inform and empower patients, families, and caregivers.

Symptoms of Atonic Seizure

Atonic seizures present with symptoms that can be subtle or dramatic, but all share a sudden and profound loss of muscle strength. Recognizing these symptoms is crucial for timely diagnosis and effective management.

Main Symptom	Description	Common Effects	Source(s)
Sudden Limpness	Abrupt loss of muscle tone	Falls, head drops, trunk sway	1 3 8
Brief Duration	Lasts only seconds	Rapid recovery, but risk of injury	1 8
Focal Onset	May affect specific body parts	E.g., right leg, trunk	1 8
Cognitive Signs	May include impaired awareness	Confusion or loss of equilibrium	1 3 8

Table 1: Key Symptoms of Atonic Seizure

Recognizing Atonic Seizures

Atonic seizures most often manifest as a sudden loss of muscle strength, causing the person to collapse or experience a head nod. This is due to a brief interruption in the brain’s ability to maintain muscle tone. The seizure itself tends to last only a few seconds, but the aftermath—a fall or injury—can be significant.

• In some cases, the atonia may be localized, affecting only one limb or the trunk, as seen in rare partial atonic seizures 1.
• Head drops and trunk sways are particularly characteristic in children with atonic variants of certain epilepsy syndromes 8.
• The suddenness of these attacks makes them particularly dangerous, as there is no warning and little time to react.

Additional Features

Not all atonic seizures are generalized. Some can start focally, affecting just one limb or one side of the body, sometimes accompanied by impaired balance or equilibrium 1. In children, atonic seizures may be mistaken for clumsiness or attention problems, especially if the episodes are subtle or occur frequently 8.

Other possible symptoms include:

• Mild confusion immediately after the event.
• Temporary loss of awareness.
• In rare cases, atonic seizures may be part of a more complex seizure pattern (e.g., myoclonic-atonic seizures) with additional features like eyelid or facial twitching 3.

Types of Atonic Seizure

Not all atonic seizures are the same—variability in their presentation and underlying causes creates distinct subtypes. Understanding these differences can help tailor diagnosis and treatment.

Type	Description	Key Features	Source(s)
Generalized Atonic	Sudden loss of tone in whole body	Falls, "drop attacks"	4 5 6
Focal Atonic	Loss of tone in specific body part	E.g., right leg, trunk	1 8
Myoclonic-Atonic	Brief jerk (myoclonus) followed by atonia	Seen in EMAtS/MAE	2 3 7
Syndrome-Specific	Linked to epilepsy syndromes	BECTS, Lennox-Gastaut, etc.	3 8

Table 2: Main Types of Atonic Seizure

Generalized Atonic Seizures

These are the classic "drop attacks"—a sudden, bilateral loss of muscle tone resulting in collapse. They are often seen in severe epilepsy syndromes and are a major cause of injury 4 5 6.

Focal (Partial) Atonic Seizures

Focal atonic seizures are less common and involve loss of tone in a localized area, such as just one limb. These can be mistaken for weakness or clumsiness but are actually the result of localized brain dysfunction 1 8.

Myoclonic-Atonic Seizures

Sometimes called "myoclonic-astatic" seizures, these involve a brief muscle jerk (myoclonus) immediately followed by atonia. This pattern is especially characteristic of epilepsy with myoclonic-atonic seizures (EMAtS), also known as myoclonic-atonic epilepsy (MAE) or Doose syndrome 2 3 7.

Syndrome-Specific Variants

Atonic seizures can be a feature of specific epilepsy syndromes:

• Lennox-Gastaut Syndrome (LGS): Notorious for frequent atonic seizures, often resistant to medication 5 6.
• Benign Childhood Epilepsy with Centrotemporal Spikes (BECTS): Atonic variant (atonic-BECTS) may present with frequent head drops and trunk sways in young children 8.
• Sturge-Weber Syndrome (SWS): May present with atonic and myoclonic-atonic seizures 7.

Causes of Atonic Seizure

The underlying causes of atonic seizures are diverse, encompassing genetic, structural, and sometimes unknown factors. Understanding these roots is key to advancing treatment and management.

Cause Type	Example/Details	Impact on Seizure Type	Source(s)
Genetic	SLC6A1 mutations (GABA transporter dysfunction)	Myoclonic-atonic seizures	2 3
Structural	Brain malformations, chromosomal translocations	Focal or generalized atonia	3 8
Syndromic	LGS, BECTS, SWS	Multiple seizure types	3 7 8
Unknown/Idiopathic	No clear cause identified	Isolated atonic seizures	1 8

Table 3: Major Causes of Atonic Seizure

Genetic Causes

A growing body of evidence points to specific genetic mutations as culprits in atonic seizures, particularly in myoclonic-atonic epilepsy (MAE/EMAtS). Mutations in the SLC6A1 gene, which affects GABA neurotransmitter transport, have been identified in several patients with this seizure type 2 3. This insight is helping to refine diagnoses and may open doors to targeted therapies.

Structural and Chromosomal Abnormalities

Structural brain abnormalities or chromosomal translocations can disrupt neural networks, leading to atonic seizures. For example, a balanced chromosomal translocation disrupting the SLC6A1 gene has been documented to trigger atonic and myoclonic-atonic seizures in children 3. Brain imaging may sometimes reveal subtle malformations, particularly in children with early-onset or treatment-resistant atonic seizures 8.

Syndromic Associations

Atonic seizures frequently occur as part of broader epilepsy syndromes:

• Lennox-Gastaut Syndrome (LGS): Characterized by multiple seizure types, including frequent atonic seizures, often with cognitive and behavioral challenges 5 6.
• BECTS (Atonic Variant): Some children with atonic-BECTS develop atonic seizures early in life, often alongside language or cognitive delays 8.
• Sturge-Weber Syndrome: This neurocutaneous disorder can also feature myoclonic-atonic seizures 7.

Unidentified or Idiopathic Causes

In some cases, no specific cause can be found. These cases are termed "idiopathic" and may still respond to treatment, but ongoing research aims to uncover hidden genetic or structural contributors 1 8.

Treatment of Atonic Seizure

Managing atonic seizures is a challenge, particularly because they often resist standard anticonvulsant therapies. Fortunately, a range of medical and surgical options are available, with ongoing research improving outcomes.

Treatment	Approach/Method	Effectiveness/Considerations	Source(s)
Antiepileptic Drugs	Valproic acid, lamotrigine, others	Often first-line, variable results	1 3 8
Cannabidiol (CBD)	Add-on therapy	>50% reduction in many children	7
Immunotherapy	Steroids, IVIG	Effective in atonic-BECTS variant	8
Corpus Callosotomy	Surgical disconnection	Highly effective, surgical risks	4 5 6
Vagus Nerve Stimulation (VNS)	Implanted device	Moderate benefit, fewer complications	5 6

Table 4: Main Treatment Approaches for Atonic Seizure

Antiepileptic Drugs (AEDs)

First-line therapy for atonic seizures typically involves AEDs:

• Valproic acid is frequently used and can be highly effective in some patients, especially those with EMAtS/MAE 3 8.
• Lamotrigine and other AEDs may be added if seizures persist 3.
• Carbamazepine and certain benzodiazepines may actually worsen atonic seizures in some cases (e.g., atonic-BECTS), so medication choice is critical 8.

Cannabidiol (CBD)

Recent studies have shown that cannabidiol, a non-psychoactive compound derived from cannabis, can significantly reduce atonic and myoclonic-atonic seizures in children with refractory epilepsy. In one multicenter study, over half of the children experienced a greater than 50% reduction in seizure frequency, with a few achieving complete seizure freedom. Side effects were generally mild 7.

Immunotherapy

For specific subtypes, such as atonic-BECTS, immunomodulatory therapy (steroids, IVIG) has shown promise, sometimes leading to complete remission. This approach is particularly beneficial when atonic seizures are associated with cognitive or behavioral decline 8.

Surgical Treatments

When medications fail, surgery is considered:

• Corpus Callosotomy (CC): This procedure severs the corpus callosum (the main connection between brain hemispheres) to prevent the spread of seizure activity. It is particularly effective for atonic and tonic seizures that cause falls, with 70–85% of patients experiencing significant reduction in seizure frequency. However, it carries a risk of “disconnection syndrome” and, less commonly, other complications 4 5 6.
• Vagus Nerve Stimulation (VNS): This involves implanting a device that sends electrical impulses to the vagus nerve. It is less effective than CC for atonic seizures but is associated with fewer surgical risks and milder side effects, such as hoarseness 5 6.

Individualized Treatment Plans

The choice of treatment depends on many factors:

• Age, seizure frequency, and injury risk.
• Underlying syndrome or genetic findings.
• Previous response to medications.
• Family and patient preferences.

In some cases, a combination of therapies may be used to achieve the best outcome.

Conclusion

Atonic seizures are a complex and challenging seizure type that require careful diagnosis and individualized management. While ongoing research continues to refine our understanding and treatment options, many patients can achieve substantial improvement in seizure control and quality of life.

Key Points:

• Atonic seizures cause sudden loss of muscle tone, often resulting in falls or head drops 1 3 8.
• Types include generalized, focal, myoclonic-atonic, and syndrome-specific variants 1 2 3 8.
• Causes range from genetic mutations (e.g., SLC6A1), to structural brain abnormalities, to idiopathic origins 2 3 8.
• Treatment options include antiepileptic drugs (notably valproic acid), cannabidiol, immunotherapy, corpus callosotomy, and vagus nerve stimulation 3 4 5 6 7 8.
• Individualized care and ongoing research are critical to improving outcomes and minimizing risks for those living with atonic seizures.

By staying informed and working closely with healthcare providers, families and patients can navigate the challenges of atonic seizures and find the most effective, safest treatments for their unique needs.