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An atonic seizure involves sudden loss or diminution of muscle tone without apparent preceding myoclonic or tonic features. Atonic seizures are very brief (<2 seconds) and may involve the head, trunk or limbs. Atonic seizures often occur in individuals with intellectual impairment.

NOTE Atonic seizures are one type of seizure that can result in a "drop attack", other causes of drop attacks include myoclonic (especially in younger children), tonic and myoclonic-atonic seizures.

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