In which areas of CNS do lesions typically produce footdrop?
Foot-drop can occur due to damage of the relevant circuitry in the pyramidal/cortico-spinal tract. This tract starts in the motor cortex and descends through the brainstem where it crosses over in the medulla to the other side. Descending fibers then communicate with the alpha motor neuron which stimulates muscle contraction. Another site for foot drop can occur by a compression neuropathy of the peroneal nerve (typically just below the knee on the lateral aspect of the lower leg involved).
A peroneal compression neuropathy is not caused by MS.
A. Scott Nielsen MD MMSc
Neurologist and MS Specialist at Kaiser Permanente