Which of the following is not a cause of absent ankle jerks and up-going plantars?

**Core Concept**
Absent ankle jerks and up-going plantars are indicative of an upper motor neuron lesion affecting the S1 nerve root, which is responsible for ankle reflexes. This clinical presentation is often associated with conditions like spinal cord injury, stroke, or multiple sclerosis.

**Why the Correct Answer is Right**
The correct answer is likely to be a condition that does not involve an upper motor neuron lesion or affect the S1 nerve root. The mechanism behind absent ankle jerks and up-going plantars involves damage to the descending motor tracts, which inhibits the reflex arc and leads to a decrease in the reflex response. The up-going plantars are a sign of a positive Babinski sign, indicating a disruption in the corticospinal tract.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might be a condition like Guillain-Barré syndrome, which affects the peripheral nerves and can lead to absent ankle jerks. However, it would typically present with areflexia (absence of reflexes) rather than up-going plantars.

**Option B:** This option might be a condition like peripheral neuropathy, which can also lead to absent ankle jerks due to damage to the peripheral nerves. However, it would not typically cause up-going plantars.

**Option C:** This option is likely to be a condition like spinal stenosis or a herniated disc, which can cause compression of the cauda equina and lead to absent ankle jerks. However, it would not typically cause up-going plantars.

**Clinical Pearl / High-Yield Fact**
Remember that absent ankle jerks and up-going plantars are a classic sign of an upper motor neuron lesion, and this clinical presentation should prompt further investigation for conditions like spinal cord injury or stroke.

**Correct Answer: C.** Spinal stenosis or a herniated disc