Why are legs so often affected by MS?

Here is My Question:
I have that often with MS, one side of your body is impacted but mostly the legs. My question is why does the leg most of the time start to effect with people with MS? Would a medication for MS like Avonex now be better or Neurotin for pain relief in my leg?  I'm confused why the one side leg plays up in many people with MS.

Answer:
Pain of any kind is rarely a sign of new MS activity. The exceptions include the pain of optic neuritis worsening with movement of the eye and the rare patient with transverse myelitis and a swollen spinal cord In these cases, the pain seems to be caused by inflammation involving the lining of the nervous system in the area of involvement (called the meninges).

The more common chronic painful sensations in MS are referred to as neuropathic pain. This pain pain is attributed to old areas of scaring and remodeling in the nervous system.  Neuropathic pain from MS is often described as burning or burning alternating with freezing. An alternative type of neuropathic pain involves perceiving cold stimuli and pressure  applied to the leg as painful. Often these painful sensations are associated with constant or intermittent pins and needles (paresthesia), electrical shocks or jolts, jabbing sensations, itching or formications (creepy crawley sensations or sensation that water is dripping down the leg). 

Some people just describe a vague severe aching sensation deep in the leg that doesn’t appear to be coming from the bones or joints. A specific type of paroxysmal neuropathic pain is called neuralgia. This is a sudden stabbing or slashing sensation in the distribution of a nerve that occurs repeatedly during the day.

Pain with a palpable location or mechanical in nature (e.g. only with external rotation of the hip), particularly when involving a joint or a tendon, is not directly related to MS. Neuropathic pain may worsen with certain activities but will be present all the time and not directly attributable to a joint, tendon or muscle injury.

Now to answer your specific questions:

1. Why are legs involved by MS before other parts of the body? This is explained by the organization of your nervous system. All information going to the legs from the nervous system must pass down the entire length of the spinal cord whereas information going to the arms only needs to reach the upper spinal cord (the cervical region). There is simply more cumulative opportunity for pathways to be involved that will affect the legs.

2. Why does one side tend to act up more often in any individual person with MS? The most common areas for symptomatic reactivation of MS (relapses) are previous areas of involvement. Therefore, if you experience a relapse involving the right leg, future relapses are more likely to affect the right leg than the left leg.

3. Would Neurontin (gabapentin) or Avonex help? Gabapentin may be helpful if this is neuropathic pain from MS. Avonex will not be helpful for this pain.

Revere (Rip) Kinkel MD
Director of the Multiple Sclerosis Program
Professor of Clinical Neurosciences
University of California San Diego