Atonic Seizures

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Infographic created by Aliana Gordon

By: Aliana Gordon

Atonic seizures occur when there is a loss of electromyographic activity, which controls the muscle movements in the body. This can occur in one part of the brain that correlates to the loss of a specific region of the body, known as a focal motor atonic seizure. Typically, it affects both sides resulting in a generalized onset atonic seizure. It is also referred to as akinetic seizures, drop attacks, or drop seizures because of the sudden loss of muscle tone that tends to lead someone to fall. Atonic means to be without tone but is often confused with astatic which is the loss of erect posture (1).

What Happens

Atonic seizures, or drop attacks, last approximately 1-2 seconds in which the muscles in the neck, trunk, and limbs lose their tone (1). The person’s body will become limp and typically fall towards the floor. During the fall, the person could remain conscious or experience a brief loss of consciousness but may regain it upon striking the floor, associated with myoclonic-astatic seizures (1,2). The person’s eyelids may droop and be nodding their head continuously. The attack could be fragmentary, where only one limb falls, or it could be a complete attack involving the complete loss of tone.

A series of myoclonic jerks can occur before muscle tone is lost and are indicative that an atonic seizure could shortly follow. Myoclonic jerks can be related to sudden spasming and are often experienced by people as they are falling asleep. Atonic seizures are also present with tonic seizures when the body stiffens during an electrical disturbance in the brain.

Seizures may last up to one minute in duration but are typically less than 10 seconds. Symptoms of seizures can vary in terms of consciousness and ability to return to activity following the event. However patient care and well-being are always of the utmost priority. First aid may be necessary for the event of an injury and hospitalization may be imperative depending on the severity of the seizure.

“Patient care and well-being are always of the utmost priority.”

The occurrence of an atonic seizure may be confused with other health concerns. An atonic seizure can be mistaken for breath-holding spells when one’s heart rate slows causing them to faint. Syncope can also cause someone to suddenly fall as a result of their blood settling below their diaphragm causing their blood pressure to drop. Additionally, cataplexy can be mistaken for an atonic seizure with a sudden decrease in muscle weakness.

Causes

The exact cause is typically unknown for what could instigate this type of seizure. Preliminary theories have pointed towards genetic changes or traumatic brain injuries. It is more common within children who grow out of it by adulthood but could still occur to anyone.

How does it relate to epilepsy?

It is commonly occurring in children with symptomatic generalized epilepsy syndromes. This type of seizure may be associated with syndromes such as the Doose, Dravet, or Lennox-Gastaut (1,4). Lennox-Gastaut syndrome is a rare childhood epilepsy syndrome and could induce clusters of seizures in a day. In addition, certain characteristics that have been observed with the Lennox-Gastaut and atonic seizures are the slow spike-and-wave activity on electroencephalogram (EEG) (5). The spike-and-wave activity indicates the action potential of a neuron which allows muscles to contract. An atonic seizure can display varying spike-and-wave complexes from 1 Hz to more rapid activity. In comparison, Lennox-Gastaut spike-and-wave activity occurs between 1.5 Hz to 2.5 Hz. These frequencies in comparison to a normal EEG analysis can be seen in the following image. A healthy 22-year-old EEG is indicated by a black arrow in the image (A) and displays a usual 6 Hz to 7 Hz theta frequency. The other image (B) displays a gray arrow pointing at the constant lower frequency of theta in a 35-year-old who has right temporal lobe epilepsy (6).

Treatments

To counteract atonic seizures, the most common treatment is the use of medication.

Common anti-seizures medication is (2):

  • Ethosuximide (Zarontin)
    •  most commonly used for the first drug
  • Valproic acid (Depakene)
    • not recommended for those who are pregnant or who may want to become pregnant
  • Lamotrigine (Lamictal)
    • fewer side effects but may be less helpful
  • Clobazam (Onfi)
    • Commonly used for Lennox-Gastaut syndrome

Implants such as the vagus nerve stimulator (VNS) can be used to stimulate the left vagus nerve with electrical charges to your brainstem (7). The VNS is typically used along with medication.

Certain diets have also been seen to help control seizures, especially ketogenic, low glycemic, and modified Atkins. Early theories suggest the ketogenic diet requires the brain to gather various sources of energy rather than glucose. The diet is characterized by having 70% – 80% of your diet being fats, 20% protein, and 5% – 10% of it is carbohydrates. Carbohydrates, commonly referred to as carbs, are the main energy source of our bodies; by reducing the number of carbs, our bodies have to search for other means of energy. Carbohydrate reduction forces the body to utilize fats as an energy replacement. The success of these treatments is poorly understood yet continue to yield statistically significant results (8).

  • 40%-50% of children on the keto diet have 50% fewer seizures
  • 10%-20% of children receive more than 90% reduction in seizures

This figure compares the ketogenic diet (KD), medium-chain triglyceride (MCT), low glycemic index treatment (LGIT), modified Atkins diet (MAD) and the modified ketogenic diet (MKT) (9).

Summary

Atonic seizures occur when the electricity of the muscle cells have a loss of activity resulting in the loss of muscle tone in the body for typically 1 to 2 seconds with no clear explanation for why it occurs. The person may have a fragmentary attack only losing tone in one region or a complete attack losing all tone. The typical characteristics include droopy eyelids, head nodding, and myoclonic jerks. Seizures can often get confused with other health concerns such as breath-holding spells, syncope, and cataplexy.

This type of seizure is typically occurrent in symptomatic generalized epilepsy syndromes such as Doose, Dravet, or Lennox-Gastaut. The use of medication and a change of diet has yielded a beneficial reduction in the occurrence of seizures, with some seeing a reduction greater than 90%.

Resources

(1) “Atonic Seizure – an Overview | ScienceDirect Topics.” Sciencedirect.com, 2017, www.sciencedirect.com/topics/medicine-and-dentistry/atonic-seizure. Accessed 11 Nov. 2020.

(2) “Atonic Seizures | Cedars-Sinai.” Cedars-Sinai.org, 2020, www.cedars-sinai.org/health-library/diseases-and-conditions/a/atonic-seizures.html. Accessed 11 Nov. 2020.

(3) “Seizures – Symptoms and Causes.” Mayo Clinic,  , 2020, www.mayoclinic.org/diseases-conditions/seizure/symptoms-causes/syc-20365711. Accessed 11 Nov. 2020.

(4) “Atonic Seizures.” Epilepsy Foundation, 2017, www.epilepsy.com/learn/types-seizures/atonic-seizures. Accessed 11 Nov. 2020.

(5) MARKAND, O. N. “Slow Spike-Wave Activity in EEG and Associated Clinical Features: Often Called ‘Lennox’ or ‘Lennox-Gastaut’ Syndrome.” Neurology, vol. 27, no. 8, 1 Aug. 1977, pp. 746–746, pubmed.ncbi.nlm.nih.gov/407485/, 10.1212/wnl.27.8.746. Accessed 15 Nov. 2020.

(6) UFO Themes. “Normal Adult EEG.” Thoracic Key, 26 July 2016, thoracickey.com/normal-adult-eeg/. Accessed 15 Nov. 2020.

(7) “Vagus Nerve Stimulation – Mayo Clinic.” Mayoclinic.org,  , 2018, www.mayoclinic.org/tests-procedures/vagus-nerve-stimulation/about/pac-20384565. Accessed 15 Nov. 2020.

(8) “Ketogenic Diet For Epilepsy / Seizures.” Cleveland Clinic, 2020, my.clevelandclinic.org/health/treatments/7156-ketogenic-diet-keto-diet-for-epilepsy. Accessed 15 Nov. 2020.

(9) Schoeler, Natasha E, and J Helen Cross. “Ketogenic Dietary Therapies in Adults with Epilepsy: A Practical Guide.” Practical Neurology, vol. 16, no. 3, 23 Feb. 2016, pp. 208–214, pn.bmj.com/content/16/3/208, 10.1136/practneurol-2015-001288. Accessed 16 Nov. 2020.

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