Spinal cord damage and pain

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Today I want to spend some time talking about spinal cord.  Can the spinal cord be a pain generator?  The spinal cord is part of the central nervous system and very important.  The spinal cord has a covering surrounding it.  This is often described as similar to a foot with a sock on.  The foot would be the spinal cord and the sock is the thecal sac.  The thecal sac is made up of 3 layers.  The outermost layer is the dura mater.  The middle layer is the arachnoid and the inner layer is the pia mater. 

When we order an MRI, we can see the thecal sac to an extent.  We can see the spinal cord with CSF surrounding it.  On the outside of the CSF we can see a dark layer that is the dura.  Often it is easier to visualize dural sac abutment with indentation than the actual dura mater. 

When disc damage is suspected, an MRI is often ordered to assess the disc damage.  The seriousness of disc damage is often seen with nervous tissue abutment or compression.  The most serious would be compression of the spinal cord and then nerve roots.  Compression would be smashing of the spinal cord or nerve root by the disc.  Abutment would be touching but not smashing the spinal cord or nerve root.  Both abutment and compression can cause neurological symptoms and pain. 

As I covered in prior podcasts any disc herniation will have nerve involvement even without nerve root or spinal cord abutment or compression.  Damage to a disc will cause recurrent meningeal nerve damage and will lead to potential disc pain.  As seen on podcast 10, disc herniations will lead to an increase of the recurrent meningeal nerve in the disc in places nerves should not be.  This can lead to discogenic pain even with normal activities.

I have talked a lot about disc herniations leading to radiculopathy or myelopathy.  When a disc abuts or compresses a nerve root or the spinal cord we can have serious implications.  Most nerve root or spinal cord compression would be an urgent surgical referral.  Most nerve root or spinal cord abutments can be managed conservatively. 

Today I want to cover disc herniations that do not abut or compress nerve roots or the spinal cord, but do abut the dura mater.  Does this have the ability to show symptoms?  Today’s study is the Innervation of the Spinal Dura Mater by M A Edgar and S Nundy in the Journal of neurosurgery and psychiatry.  This study was published in 1966.  I know this is a very old study, but I do believe there are some really useful findings in this study. 

This study covers the history of nerve supply to the spinal dura mater.  They go back to 1845 when Von Luschka saw that branches of the ramus remained entirely outside the spinal dura mater, but were seen close to the surface.  In 1857 another researcher saw that nerves ran along the ventral or front surface of the dura mater and then entered the dura.  Another study in 1904 showed that the nerves went to the ventral surface of the dura mater and then entered.  Then in 1940 it was seen that the nerves went to the surface of the dura, but did not enter the dura.  Clarification was needed and that is the reason for this study.

This study showed that the recurrent meningeal nerve does go to the dura in 3 courses.  The first is around the base of the pedicle.  The second is a direct pass to the ventral dura in the spinal canal. The 3^rd is longitudinally within the epidural tissue.  This study showed that the front or ventral aspect of the dura mater has numerous nerves and even free nerve endings.  This study showed that the back or dorsal aspect of the dura did not have any nerve innervation.   They reported that nerves going to the ventral aspect of the dura correlates with disc herniations that abut the dura and cause pain.  They reported that with no nerves found on the dorsal or back of the dura this correlates with no pain with lumbar punctures.

They reported that these nerves have a pain function in the dura.  So, to answer my question at the beginning of the podcast, can the spinal cord be a pain generator the answer is yes.  The answer is also no.  It appears that the front or ventral aspect of the cord can be a pain generator and the posterior or dorsal aspect is less likely to be a pain generator.

Real World

I had a young patient with persistent cervical and upper thoracic pain after a MVC.  There were no radicular or myelopathic findings on the initial exam and treatment was started.  After 1 month of care she was not making the progress I would expect.  Her cervical and upper thoracic spine were still in a lot of pain.  I ordered a cervical MRI. 

Her MRI showed a small central protrusion type disc herniation with no neural canal stenosis and no nerve root abutment.  This herniation was abutting and indenting the thecal sac.  This abutment was minor and only slightly indented the thecal sac. 

The patient was wondering how  such a small disc herniation could cause so much pain.  First I told her that the disc herniation may not be the cause of pain or the largest contributor to her pain.  There are a lot of pain generators in her spine that could cause the pain.  Second I t her that this  disc herniaiton  does correlate with persistent pain in the cervical and thoracic spine. 

This disc herniation is abutting the ventral or front aspect of the dura.  As seen in today’s study there are nerves in the dura that have pain function.  This correlates with some of her pain.  This would not be radicular or arm pain, but more diffuse pain.  This type of pain is felt in the cervical spine and upper thoracic spine.

It is also important to think about the disc herniation as another pain generator.  The herniation is tearing of the disc with the inside of the disc coming out.  This will also cause pain mediated through the recurrent meningeal nerve.  This disc damage will also be felt as diffuse and often cervical and upper thoracic spine. 

Over time this type of herniation typically resorbs and will no longer have dura abutment.  Unfortunately, this will not typically resolve the pain.  As I talked about in prior podcasts the disc herniation will cause the ingrowth of the recurrent meningeal nerve.  This ingrowth will be in parts of the disc that were never meant to have pain.  Once the nerve grows inside the disc pain can be felt with normal activities. 

This is the type of patient that typically does well with active care, but once released the symptoms come back.  This is the type of patient that proper explanation of their injuries and future problems is crucial for the attorney and insurance adjuster to understand the case and come to a fair settlement.  This will be a permanent injury with prolonger symptoms that will never fully resolve, but are often managed well.