A student asks whether spasticity can develop in a patient with a complete SCI. Which statement is MOST accurate?

A student asks whether spasticity can develop in a patient with a complete SCI. Which statement is MOST accurate?

• A. Spasticity only occurs in incomplete injuries because it requires descending supraspinal input
• B. Spasticity cannot occur in any SCI because the reflex arc is always disrupted
• C. Spasticity occurs only during spinal shock and resolves completely afterward
• D. Spasticity can occur in both complete and incomplete injuries, as it is mediated by spinal reflex circuits below the level of the lesion

Answer: (D)

Spasticity after a spinal cord injury comes from loss of brain-based inhibition, which makes the spinal reflex circuits below the injury hyperexcitable. Even when a lesion is complete and there’s no descending input to the lower segments, the reflex pathways below the level of injury can still fire strongly in response to stretch or movement. As spinal shock passes, these circuits can become unusually responsive, leading to a velocity-dependent increase in muscle tone and brisk reflexes in muscles below the lesion. This can happen in both complete and incomplete injuries, depending on timing and individual factors. The key idea is that spasticity arises from the spinal reflex system below the lesion, not from the presence of supraspinal input, and it is not limited to the period of spinal shock.

Spasticity after a spinal cord injury comes from loss of brain-based inhibition, which makes the spinal reflex circuits below the injury hyperexcitable. Even when a lesion is complete and there’s no descending input to the lower segments, the reflex pathways below the level of injury can still fire strongly in response to stretch or movement. As spinal shock passes, these circuits can become unusually responsive, leading to a velocity-dependent increase in muscle tone and brisk reflexes in muscles below the lesion. This can happen in both complete and incomplete injuries, depending on timing and individual factors. The key idea is that spasticity arises from the spinal reflex system below the lesion, not from the presence of supraspinal input, and it is not limited to the period of spinal shock.