Atonic seizures are a specific type of seizure characterized by an abrupt and brief loss of muscle tone. This particular seizure type affects an individual’s ability to maintain posture and can impact physical function.
Understanding Atonic Seizures
Atonic seizures are defined by a sudden and complete, or partial, loss of muscle tone. This abrupt loss of muscle strength often causes individuals to go limp and fall, which is why they are frequently called “drop attacks” or “drop seizures.” The manifestation can vary from a subtle head drop, where only the neck muscles relax, to a full body collapse where the person slumps or falls to the ground. If an individual is holding something during an atonic seizure, they may drop it due to the sudden loss of muscle control.
These seizures are remarkably brief, typically lasting less than 15 seconds, and often less than two seconds. Despite the sudden collapse, consciousness is usually maintained, or at most, briefly impaired, and individuals often return to full awareness immediately after the seizure ends. This quick recovery means that if a fall occurs, the person can often get back up straight away once muscle tone returns. Atonic seizures differ from other seizure types, such as tonic-clonic seizures, where there is initial stiffening followed by rhythmic jerking, or absence seizures, which involve brief staring spells without a loss of muscle tone.
Causes of Atonic Seizures
Atonic seizures frequently occur not as isolated events but as a component of broader epilepsy syndromes. One of the most recognized associations is with Lennox-Gastaut Syndrome (LGS), a severe form of childhood epilepsy characterized by multiple seizure types and often intellectual disability. In LGS, atonic seizures are common alongside tonic and atypical absence seizures, contributing to the challenges faced by affected individuals. Other epilepsy syndromes, such as Doose syndrome, also known as Epilepsy with Myoclonic-Atonic Seizures (EMAS), similarly feature atonic seizures as a prominent symptom, typically emerging in early childhood.
The underlying reasons for atonic seizures can stem from various neurological factors. Structural brain abnormalities, including malformations, past brain injuries, strokes, or tumors, can disrupt normal brain electrical activity and lead to these seizures. Additionally, central nervous system infections can contribute to their development. Genetic factors also play a role, with some individuals inheriting a predisposition to epilepsy. In many instances, particularly in syndromes like LGS, the exact cause of atonic seizures remains unknown.
Diagnosing Atonic Seizures
Diagnosing atonic seizures begins with a detailed medical history. Eyewitness accounts are particularly valuable due to the seizure’s brevity. Descriptions of what happened before, during, and immediately after the sudden loss of muscle tone, including any falls or injuries, provide essential clues. Video recordings of the events can also offer precise information.
Electroencephalogram (EEG) is a primary diagnostic tool. During an atonic seizure, the EEG may show specific patterns, such as generalized polyspike-wave discharges, confirming the diagnosis and distinguishing it from other seizure types. Neuroimaging techniques, including Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) scans, are often employed to identify any underlying structural brain abnormalities like tumors, lesions, or previous injuries. These imaging studies also serve to rule out other conditions that might mimic atonic seizures, such as transient ischemic attacks or other causes of sudden falls like cardiac issues or syncope.
Treatment Approaches for Atonic Seizures
Treatment for atonic seizures aims to reduce their frequency and minimize the risk of injury from falls. The primary approach often involves anticonvulsant medications. Common medications used include valproic acid, lamotrigine, topiramate, levetiracetam, zonisamide, rufinamide, and benzodiazepines like clobazam. Atonic seizures can be particularly challenging to control with medication alone, and finding the most effective drug or combination may require careful adjustment and monitoring.
When medications are not sufficiently effective, non-pharmacological interventions are considered. The ketogenic diet, a high-fat, low-carbohydrate, and controlled-protein regimen, has shown promise, particularly in children with difficult-to-control seizures. Another option is Vagus Nerve Stimulation (VNS), which involves surgically implanting a device that sends electrical impulses to the brain via the vagus nerve. Epilepsy surgery may be considered, such as a corpus callosotomy, which involves surgically severing nerve fibers connecting the two hemispheres of the brain to prevent generalized seizures from spreading and reduce fall severity. Protective headgear, such as helmets, may be recommended due to the high risk of injury.