Neck Injury With Arm Pain, Negative MRI! What’s Up?
It is not uncommon to find a person suffering from whiplash injury who complains of some type of symptoms radiating from the shoulder, down to the arm and hand. The obvious first assumption is that there is a radiculopathy being caused by a “pinched” nerve in the neck. However, it is also not uncommon to find a negative MRI: meaning, there is no structural “pinching” of the nerve! So now what?
In his article, L Gifford states that the nerve sheaths can become hypersensitive and generate ectopic impulses as “a direct result of direct mechanical insults, changes in circulatory perfusion or inward diffusion of irritative inflammatory chemicals from damaged or disordered adjacent soft tissues…” Basically, the nerve can become irritated from mechanical issues, vascular problems, or chemical irritants, most of which are not seen on an MRI.
Nerve roots can be physically injured by extreme spinal movements, think the head being whipped backwards or sideways, or less violent motions if there are degenerative conditions present.
Practical Point: in a patient that has pre-existing disc or facet joint degeneration, the opening for the nerve root is already compromised. It is then possible for less extreme motions to momentarily put pressure on the nerve during rapid head movement. This then can initiate an inflammation of the nerve root producing symptoms down the arm.
Nerve roots can become sensitized by changes in the local circulation. Anything that reduces the space where nerve roots exit the spine can result in restricted circulation. This produces a slowdown and back pressure in the blood vessels, which decreases the blood flow to the nerve root itself.
Practical point: Degenerative changes in disc or facet joints, reduce the space around the nerve root and its blood vessels. Insult to the blood vessels can result in decreased blood flow to the nerve and result in an over sensitization of the nerve.
When soft tissue such as joint capsules, muscles, and ligaments are injured, the natural response is inflammation. This process causes a release of an irritating chemical in the area. If they spill on to the nerve root, it is like pouring batter acid on the tissue! This results in an over sensitization of the nerve root.
Practical Point: Inflammation from surrounding injured tissue can irritate the adjacent nerve root and create radicular type symptoms.
Thankfully, with the right questions on a history and a few specific tests, these injuries can be documented.
In summary, direct physical compression of a nerve root is not necessary for it to be injured and alter its sensitivity. This means discs do not have to be directly “pinch” nerve tissue to produce pathological changes.
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Gifford L. Acute low cervical nerve root conditions: symptom presentations and pathobiological reasoning. Manual Therapy. 2001;6(2): 106–115.