Atonic Seizures

Atonic seizures are associated with a sudden loss or decrease of muscle tone and frequently cause patients to fall. This type of drop attack may be observed in individuals suffering from distinct forms of epilepsy.

The disease is related to the following processes:  endocrine 

Presentation

In general, AS are considered a form of generalized seizure. This concept has recently been challenged and it has been pointed out that focal seizures with atonic features may indeed imply epilepsy [7]. In this context, the following may be stated:

  • AS as a manifestation of generalized epilepsy most commonly affect the muscles of the trunk and cause patients to fall slowly. Patients who sustained such drop attacks frequently present with traumatic lesions of head, neck, or other regions of their body. Of note, drop attacks may also be reported by those suffering from clonic seizures.
  • Focal loss or diminution of the muscle tone may result in head dropping, paresis or paralysis of the extremities [8]. Focal AS are not to be confounded with Todd's paresis, a post-ictal phenomenon that may be observed in epilepsy patients.

According to a recent study regarding the circadian patterns of AS, such seizures only occur in wakefulness [9]. Consciousness is generally maintained. AS typically last seconds to minutes.

Additional cognitive and motor deficits are frequently reported and may comprise learning disability, impaired coordination, spasticity and hemiparesis as well as consequent gait disorders [1].

Workup

Video-electroencephalography (EEG) with concomitant electromyography should be carried out to confirm central nervous system involvement and muscular hypotonia [3]. With regards to the former, high-amplitude spike-and-slow-wave discharges have been reported to immediately precede AS [8]. These signals may be followed by diffuse background suppression. AS may originate from single brain regions, e.g., the frontal, temporal, parietal, or occipital lobes, or result from multifocal anomalies [1].

Furthermore, neuroimaging may be helpful. In this context, magnetic resonance imaging is more sensitive technique and is thus preferred over computed tomography scans [10]. The absence of anomalies does not permit to rule out AS, though. In general, organic abnormalities are more likely to be detected in patients presenting with focal seizures than in those suffering from generalized seizures.

If neither study yields convincing results but differential diagnoses like transient ischemic attack or a migraine have been ruled out, the observance of accompanying symptoms may support a tentative diagnosis of AS. These are not characteristic of AS but merely imply epilepsy [7]:

  • Symptoms are preceded by an aura.
  • Concomitant or subsequent convulsive activity.
  • Evolution of symptoms.

Treatment

Prognosis

Etiology

Epidemiology

Sex distribution
Age distribution

Pathophysiology

Prevention

Summary

Atonic seizures (AS) are a rare type of epileptic seizures characterized by a sudden reduction of a patient's muscle tone. Because affected individuals frequently fall during such epileptic attack, AS are also considered a type of drop attack [1]. Injuries sustained during falls significantly contribute to AS-related morbidity.

AS may occur in patients suffering from different types of epilepsy, mainly severe forms of childhood epilepsy (e.g., Lennox-Gastaut syndrome, myoclonic-astatic epilepsy) and epilepsy due to brain lesions endured at any point in life [2]. Accordingly, AS patients may also sustain tonic, clonic and absence seizures [3]. AS have also been related to nodding syndrome, a childhood disorder endemic to South Sudan, Uganda, and Tanzania, whose etiology remains poorly understood [4] [5].

Both anti-epileptic medication and surgery may be considered to treat AS [6].

Patient Information

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References

  1. Baraldi S, Farrell F, Benson J, Diehl B, Wehner T, Kovac S. Drop attacks, falls and atonic seizures in the Video-EEG monitoring unit. Seizure. 2015; 32:4-8.
  2. Khan RB, Marshman KC, Mulhern RK. Atonic seizures in survivors of childhood cancer. J Child Neurol. 2003; 18(6):397-400.
  3. Vining EP. Tonic and atonic seizures: medical therapy and ketogenic diet. Epilepsia. 2009; 50 Suppl 8:21-24.
  4. Sejvar JJ, Kakooza AM, Foltz JL, et al. Clinical, neurological, and electrophysiological features of nodding syndrome in Kitgum, Uganda: an observational case series. Lancet Neurol. 2013; 12(2):166-174.
  5. Dowell SF, Sejvar JJ, Riek L, et al. Nodding syndrome. Emerg Infect Dis. 2013; 19(9):1374-1384.
  6. Cukiert A, Cukiert CM, Burattini JA, et al. Long-term outcome after callosotomy or vagus nerve stimulation in consecutive prospective cohorts of children with Lennox-Gastaut or Lennox-like syndrome and non-specific MRI findings. Seizure. 2013; 22(5):396-400.
  7. Kovac S, Diehl B. Atonic phenomena in focal seizures: nomenclature, clinical findings and pathophysiological concepts. Seizure. 2012; 21(8):561-567.
  8. Zhao J, Afra P, Adamolekun B. Partial epilepsy presenting as focal atonic seizure: a case report. Seizure. 2010; 19(6):326-329.
  9. Gurkas E, Serdaroglu A, Hirfanoglu T, Kartal A, Yilmaz U, Bilir E. Sleep-wake distribution and circadian patterns of epileptic seizures in children. Eur J Paediatr Neurol. 2016; 20(4):549-554.
  10. Kuzniecky RI. Neuroimaging of epilepsy: therapeutic implications. NeuroRx. 2005; 2(2):384-393.

  • Are some idiopathic epilepsies disorders of ion channels?: A working hypothesis - S Hirose, M Okada, S Kaneko, A Mitsudome - Epilepsy research, 2000 - Elsevier


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