What is the most common acquired paralysis in a previously healthy child?

The most common acquired paralysis in a previously healthy child is Guillain-Barré syndrome. This condition is an autoimmune disorder where the body's immune system mistakenly attacks the peripheral nervous system, often following an infection. In children, it typically presents with rapid-onset weakness that can progress to paralysis. The hallmark of Guillain-Barré syndrome is ascending paralysis, which begins in the legs and may move upward, potentially affecting respiratory muscles and necessitating medical intervention.

In contrast, other options listed are distinct conditions. Myasthenia Gravis, while also an autoimmune disorder, is more chronic and usually presents with fluctuating muscle weakness rather than the acute paralysis characteristic of Guillain-Barré. Spinal Muscular Atrophy is a genetic disorder that leads to muscle weakness and atrophy due to motor neuron degeneration rather than an acquired condition. Neuromyelitis Optica is a condition that affects the spinal cord and optic nerves, often leading to vision and mobility issues, but it is less common than Guillain-Barré syndrome in terms of acute paralysis in children. Thus, Guillain-Barré syndrome stands out as the most prevalent acquired paralysis observed in previously healthy children.