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  • Michele Curatolo

Is "sciatica" a thing?


Sciatica is pain referred to the back, buttock and leg. It is a potentially misleading term that should be replaced by radicular pain or referred somatic pain.

 

Have you or anyone you know ever experienced pain radiating from your back into your leg? This pain is often referred to as “sciatica” by both the general public and healthcare professionals. However, this term can be misleading and create confusion. The confusion arises because "sciatica" implies an issue with the sciatic nerve, but this nerve is very rarely involved in what is commonly referred to as "sciatica". Furthermore, this term encompasses conditions that may not be related with "nerve" pain at all.


Let's try to make some order, with the help of the Neuropathic Pain Special Interest Group (NeuPSIG) of the International Association for the Study of Pain (IASP). Their work is published here. The recommendation is that the term “sciatica” should be abandoned. Appropriate terms are "radicular pain" and "referred pain".


Radicular pain

Radicular pain is typically perceived at the low back, buttock, leg and foot. It arises from nerves in the spine that become overly sensitive, mostly because of inflammation or compression from an herniated disc (see figure below) or a narrow spinal canal. The patient feels pain down the leg because those nerves supply the leg, but there is obviously nothing wrong with the leg, the origin being at the nerve of the spine. Along with the pain, patients may feel tingling, numbness, or even muscle weakness.



Referred somatic pain

In this case, the pain signal may start from joints, muscles, or discs of the low back, and not primarily from nerves. It is again perceived at the buttocks, the leg, and sometimes the foot, but unlike radicular pain the spinal nerves are not primarily involved.

Why would a spinal issue manifest as leg pain? Because mechanisms within the spinal cord and the brain convert a pain signal originating from the spine into pain perceived in remote areas, such as the leg. One widely accepted theory suggests that nerves from both the spine and the leg converge at the same regions within the spinal cord. From there, the signal is transmitted to the brain. The brain is then unable to discern whether the source of discomfort is the back or the leg.


While both radicular and referred somatic pain can present with very similar symptoms, differentiating the two is essential for the treatment plan.


Frequent misconceptions

  • Leg pain is "nerve pain".

    • This is not necessarily the case. Referred leg pain may have nothing to do with problems at nerves.

  • An herniated disc or narrow spinal canal ("stenosis") implies radicular pain.

    • This is wrong. An image finding is not pain. Both herniated discs and spinal stenosis may or may not cause pain, and there are many individuals with these findings who have no pain. Unfortunately, many patients with image findings of herniation or stenosis receive epidural steroid injections or even surgery that will not help if the pain is not radicular in nature.


Why does it matter?

For treatment purposes, these two conditions are fundamentally different, and have to be addressed in very different ways. The above mentioned working group has proposed criteria to differentiate the two conditions that are based on a combination of history, diagnostic tests, sensory signs such as numbness, and location of pain consistent or not with the areas supplied by spine nerves. Details can be found here.

The diagram below, taken from that publication, assists in determining the following diagnoses: 1) no radicular (neuropathic) pain, therefore likely referred somatic pain; 2) possible, 3) probable or 4) definite radicular (neuropathic) pain.




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