What condition is characterized by a sudden loss of muscle tone in children?

The condition characterized by a sudden loss of muscle tone in children is cataplexy, which is often associated with narcolepsy. Cataplexy involves brief episodes where the person experiences a loss of voluntary muscle tone, often triggered by strong emotions such as laughter, surprise, or anger. This sudden loss of muscle control can lead to weakness or collapse while remaining fully conscious, making it distinct from other conditions.

In contrast, myopathy generally refers to a disease of the muscle itself that can cause weakness but not typically a sudden loss of muscle tone in specific episodes. Epileptic seizures involve uncontrolled electrical activity in the brain, resulting in convulsions or loss of consciousness but not specifically linked to a sudden loss of muscle tone as a solo symptom. Myasthenia gravis is an autoimmune disorder characterized by weakness and fatigability of muscles, rather than a sudden drop in tone, and symptoms typically worsen with activity rather than appearing in sudden episodes.