What is the typical muscle tone below the level of the spinal lesion in spina bifida?

• A. Generally hypotonic
• B. Generally hypertonic
• C. Normal tone
• D. Spastic with clonus

Answer: (A)

In spina bifida, the lesion interrupts the motor pathways to the muscles below it from birth. Because those muscles don’t receive normal innervation or descending facilitation, they typically remain slack and show reduced resistance to movement. This results in hypotonia (flaccid paralysis) below the level of the lesion. The tone above the lesion can be different, often showing signs of upper motor neuron involvement, but the region below the lesion is characteristically hypoactive. Hypertonia or spasticity would not be the typical pattern for the muscles below the lesion in this congenital condition, and normal tone would imply intact pathways, which isn’t the case here.