What is the cause of pain radiating down the limbs?

Q: I underwent a NCV/EMG test and the reports are as follows - MNCV: CMAP could not be elicited from left peroneal nerve. Relative decrease in amplitude of left tibial nerve. Other latencies, amplitudes and conduction velocity normal. Abnormal study suggestive of chronic regenerative changes in left L3-L4 and L3-4 region (Radiculopathy). There is no evidence of neuropathy. Please explain the significance of the above test report.

A:It is often difficult for a doctor to differentiate between the two common causes of pain radiating down the lower limbs - pressure upon the nerve roots in the spinal canal or abnormality in the peripheral nerves in the lower limbs. At such times an electrical test, such as is reported above, is requested.The electrical test reported above shows that there is no abnormality in the peripheral nerves - the nerves in the lower limbs. However, there is evidence of radiculopathy. This term refers to abnormality of function in the nerve roots in the spinal canal that eventually form the nerves that travel down the lower limbs. A common cause of such radiculopathy is compression of the nerve roots in the spinal canal by bulging, degenerated intervertebral discs or, as is commonly termed, slipped discs.