I had a myelogram+nerve ultrasound last June without any problem.
It didn't help to improve my spine diseases, or to fix the spinal fusion between L2-L5, or to improve my foot drop, but it didn't cause any adverse event. It wasn't even painful, but the diagnosis didn't leave me with any hope for less pain, increased mobility or any chance of improvement of my foot drop.
Below is the summary of the 3-page long EMG results.
"Conclusion:
This is an abnormal study. There is electrodiagnostic evidence
of right L5 and S1 radiculopathy with ongoing denervation."