In an earlier post, Jim went over how to differentiate between cervical myelopathy and radiculopathy, or an upper motor lesion and lower motor lesion. Once you have made that differentiation, you have to determine where that lesion is: peripheral nerve, plexus, or spinal nerve. In this post, we're going to go over specifically how to differentiate between peripheral neuropathy and radiculopathy. I am going to focus on the upper quarter region, but the same concept will apply to the lower quarter as well. Below are a couple pictures of the peripheral nerve layouts and dermatomal patterns that I will reference throughout this post
For starters, remember that both peripheral nerve lesions and radiculopathy are lower motor neuron lesions, so they can both present with corresponding weakness and hyporeflexia. Additionally, they can sometimes present with pain (or numbness/tingling) in similar regions. Think of the ulnar nerve and C8. This is especially true due to the anatomical variation that occurs in the population. Just because a patient has radiculopathy doesn't mean they have to have symptoms centrally/proximally as well. They both can present with symptoms along the ulnar border of the hand. Other regions have more distinct differences, for example, C7 tends to refer down the middle finger and no peripheral nerve typically presents in just that region.
How Do We Differentiate Peripheral Nerve from Nerve Root?
There are several things to consider. An extremely useful assessment style is assessing muscle strength in muscles that have similar segmental input but different peripheral nerves. We'll go back to our C8 vs ulnar nerve example. Both are heavily innervated by the same segment and can present with symptoms in the same location. A key assessment feature is looking at the strength of Extensor Pollicis Longus. It is innervated by the radial nerve, but it's primary segmental input is C8. Should a patient have weakness here, we would be leaning more towards C8 radiculopathy. If it is strong, we would lean more towards ulnar neuropathy. The same concept can be applied to other areas. When trying to differentiate between L5-S1 radiculopathy and peroneal neuropathy, we look at strength of the gluteus medius and peroneals. While they share similar spinal nerve input, they have different peripheral nerve innervation (gluteus medius: superior gluteal nerve; peroneal longus/brevis: superficial peroneal nerve). Another useful assessment is neural tensioning. Should the patient's exact symptom be reproduced with it, we likely would consider the nerve involvement; however, often radiculopathy does have a neural tension component to it, so it is not as helpful as we would like. One of the best assessment techniques is using the cervical radiculopathy cluster developed by Wainner, et al:
This cluster has been shown to have high diagnostic accuracy for identifying those with cervical radiculopathy and is probably our best tool (3 positive: +LR = 6.1, 4 positive: +LR = 30.3). While one would think that pain with segmental mobility testing of the spine would be useful if pain is recreated, people can have symptoms in two locations as a result of Double Crush Syndrome or altered neurodynamics. Regardless, the most important thing is that we treat all impairments we are presented with. If the neck is stiff in someone with ulnar neuropathy, I'm still going to work on improving neck mobility. They key is that if there is research for a specific treatment for a specific diagnosis, it is important we try and identify these cases. Also, remember that there are other sources for symptoms other than peripheral nerves and radiculopathy. Patients can also present with symptoms in the exact same region due to trigger point referral patterns, local strains/sprains, a plexus, and more. Hopefully this will at least help with differentiating between two similar presentations. For a more in-depth review of examining patient's with neck pain with radiating pain, check out the lecture below: