If mri doesn't show cause of foot drop (l5s1 protusion)and emg doesn't show nerve issue and you have back and sciatica pain, could ms be a possibility?

Unlikely: Lumbar radiculopathy and peroneal neuropathy are much more likely, and sometimes the MRI findings are there but poorly understood. Further evaluation, emg/ncv of the lower extremities, and additional MRI eval for lateral recess l5s1.

Possibly: Emg would identify a peripheral nerve source for foot drop. If EMG is neg, other central nerve diseases should be considered. These would include MS and a host of other central problems. You probably want to see a neurologist for a complete examination and consideration of additional diagnostic testing

Could be: but you would need to se neurologist for that diagnosis. You mention L5/S1 protrusion, do you have that? If so, that can be a cause for your foot drop. Also there could be some sort of mononeuropathy going on, surprised EMG did not show anything. Foot drop is definitely a nerve issue and the EMG should have shown some issue. Suggest maybe getting repeat EMG with AANEM board certified doctor.