Today, we're going to talk about radiculopathy. Our objectives for today are to describe the anatomical basis for evaluation of a patient with a radiculopathy. We're going to talk about how to perform a focused clinical evaluation of a patient with a suspected radiculopathy, and how to design and interpret an electrodiagnostic evaluation of a patient with a suspected radiculopathy. Before we talk about EMG, it's important to have an understanding of the anatomy of the nerve roots. Typically, we evaluate the C5 to T1 nerve roots in the upper limb, and the L2 to S1 nerve roots in the lower limb. These are the areas where there's a lot of mobility in the spine, so they tend to be more prone to pathology. A couple definitions are dermatome, which is an area of cutaneous skin innervated by a single nerve root, and a myotome, which is a group of muscles innervated by a single nerve root. A clinical pearl is that extremely well-defined sensory deficits, such as splitting of the fourth digit where one side is numb and the other side is normal, these tend to be more consistent with a mononeuropathy than a radiculopathy. And this has to do with the fact that the dermatomes tend to overlap a lot, whereas the cutaneous innervation of individual nerves tend to be more distinct. By the same token, profound weakness, greater than three out of five weakness, is unlikely in a single-level radiculopathy. Every muscle has more than one nerve root that innervates it, and so it's unlikely that knocking out a single nerve root will cause profound weakness in a given muscle. Here you can see the upper limb root-level innervations, and it can sometimes be hard to assign pathology to a single nerve root. You can see that there's a lot of overlap, and so in some cases it can be challenging to just pin it down on a single root level. Here's the lower limb root-level innervation, and you can see here a lot of overlap between L5 and S1. Again, it can be very challenging to distinguish between these two levels when you're seeing patients clinically. One way that you can try and get at this is by using paired muscles. So the fibularis longus and gluteus medius are really good muscles for assessing L5, and the medial gastroc and the gluteus maximus tend to have a little bit more S1 innervation. So sometimes you can leverage this to localize the lesion. One other important thing to keep in mind is that if you ever end up going to mommy or daddy go to school day to talk about your job, every single elementary school child knows the gluteus maximus muscle, and they will find it absolutely hilarious when you talk about it. Etiologies for radiculopathies include disc herniation and spondylosis. Spondylosis is just arthritis of the spine, as you can see there on the left, and those are the two most common etiologies for radiculopathy. Other less common etiologies include mass lesions, infection, infiltration, demyelination, and infarction. Here you can see some of the nerve root level anatomy. It's important to keep in mind that cervical nerve roots are named for the vertebral body below the root. If you have a lateral herniation at C6, C7, that's going to tend to affect the C6 nerve root, and a posterior lateral herniation will tend to affect the C7 nerve root. On the other hand, thoracic and lumbar nerve roots are named for the vertebral body above the nerve root. If you have an L5-S1 lateral herniation, that tends to affect the L5 nerve root more, whereas a posterior lateral herniation tends to affect the S1 nerve root a little bit more. One of the things that can be challenging is a lot of times surgeons will talk about vertebral levels, whereas electromyographers, we tend to think more in terms of the individual nerve roots. So it's important to be able to translate between the two. Differential diagnosis. Differential diagnosis for radiculopathy includes a plexopathy, entrapment neuropathy, such as carpal tunnel, polyneuropathy, disorders of the motor unit, degenerative motor neuron diseases, neuromuscular junction disorders, and myopathy. The first one, degenerative motor neuron disease, can be rather challenging if you're early on in the course of a disease such as ALS. It can present in a very focal way. Musculoskeletal pathology. Here you can see an example of an ultrasound of a rotator cuff tear. And then imaging negative or idiopathic radiculopathy. Sometimes a patient presents with a radiculopathy and it's not completely clear what the cause of it is. Medical presentation. So the levels most affected by disc herniation and spondylosis are the L5 and S1 nerve roots of the lumbosacral level, and C7 at the cervical level, followed by C5 and C6. When you have patients who are referred to you for radiculopathy outside of these levels, that certainly can be the etiology, but you want to just kind of think a little bit more about your differential. For example, when patients come in with proximal leg weakness, you would want to think about something like diabetic amyotrophy, a plexopathy affecting the upper lumbar roots. And both neurologic amyotrophy and diabetic amyotrophy are characterized by excruciating pain followed by weakness and muscle wasting on examination. So when you hear this history, you want to just put your antenna up and just think a little bit more about the other things in your differential. Here you can see the physical exam for the upper limbs with the muscles and the nerve roots that are innervated. The special test that you would consider would be a Sperling's test, where you extend, rotate, and laterally deviate the neck to the affected level. And also for your mononeuropathies, you want to consider a Tenel's at the cubital tunnel and a Tenel's at the wrist. Carpal compression tests and Phalen's are also important to exclude carpal tunnel. Notice how the examiner here is isolating the individual joints when he's doing the physical exam. With a radiculopathy, it's very important to be very specific in how you do it. C5, C6, C7, C8, T1. For the lower limbs, here you can see the muscles that you would test. For the special tests, a straight leg raise would be suggestive of radiculopathy. And you can also do a tennels at the fibular neck and the medial malleolus to rule out entrapment neuropathies there. Notice he's testing long-toe flexion. That can sometimes be easier than plantar flexion. L3, L4, L5, and S1 at the lateral malleolus. If you really want to test ankle plantar flexors, this is one way to do it. Now let's move on to electrodiagnostic testing. A couple things to keep in mind about EMGs or electrodiagnostic evaluations. An electrodiagnostic study is the primary test to diagnose lower motor neuron conditions. It includes a nerve conduction study and a needle EMG. And most importantly, it's an extension of the physical examination that you just saw. Nerve conduction studies may be a little less helpful in a radiculopathy and are primarily used to rule out other differential diagnoses. You want to consider performing a sensory nerve conduction study in the distribution of the sensory complaint, especially when there's a suspicion for a mononeuropathy or a plexopathy. For example, if you're considering a C5 radiculopathy, you might consider a lateral antebrachial cutaneous sensory study. Motor nerve conduction CMAP and the F-response in H-reflex may have a little lower sensitivity and specificity, although an H-reflex may be helpful in diagnosing an S1 radiculopathy. One clinical pearl is that a reason why upper limb Fs are a little bit limited in their utility is that they're assessing the wrong levels. The median and ulnar F waves assess the C8T1 levels, and radicular pathology is commonly not in this area. So here we can see how nerve conduction studies give us insight into the anatomy of a lesion. You can see here the dorsal or the posterior root ganglia and the anterior or the ventral root. Here's the cell body of the motor neuron, which resides inside the spinal cord and the posterior dorsal root ganglia. If there's a lesion proximal to the posterior ganglia and you stimulate the sensory nerve distal to that area, you'll see a nice normal potential. That doesn't mean that sensation is not interrupted from the patient's perspective, because the circuit is interrupted. It just means that the electrical study would be normal when the lesion is proximal to the dorsal root ganglia, as it is in a radiculopathy. On the other hand, if you have a distal lesion, such as a plexopathy or a mononeuropathy, the Wallerian degeneration will proceed distally, and in that case when you stimulate, you will not get a response according to this paradigm. So the bottom line is that if a sensory response is abnormal, that argues against a radicular process or a process proximal to the posterior or dorsal root ganglia. Now let's talk a little bit about needle EMG and radiculopathy. Radiculopathies will show increased spontaneous activity, such as positive sharp waves, fibrillations, and complex repetitive discharge. The motor units will generally show high amplitude, long duration potentials with increased polyphasia and decreased recruitment. So let's take a look at a couple examples of increased spontaneous activity. Here you can see a fibrillation potential. Note how short duration and regular it is. Here you can see a classic positive sharp wave. Again, notice how regular it is. It gets a little bit trickier when you see both at once. Here's what both a positive sharp wave and a fibrillation looks like. Some people compare the sound to rain on a roof. And here we can see neuropathic motor units, long duration and polyphasic. So when you're looking for needle EMG abnormalities, the paraspinals can be very helpful in terms of localizing the lesion. In a radiculopathy, you generally have a lesion proximal to the dorsal rami. And so in that case, both the limb muscle and the paraspinal muscle will be abnormal. In the case of a plexopathy or a mononeuropathy, the lesion is distal to that branch point, and so the paraspinals are normal and the limb needle EMGs will be abnormal. So when you're approaching the needle EMG, the key is to understand that a radicular process is likely when two muscles, which are innervated by the same nerve root but different peripheral nerves, are abnormal in the EMG exam. The way I sometimes think about this is it's a little bit like playing battleship where you're trying to figure out where the lesion is. You want to make sure that you test proximal and distal muscles innervated by the same myotome to exclude a distal to proximal pattern as in a polyneuropathy. The example that I used before of the fibularis longus and gluteus medius would be an example of this principle. Muscles above and below the suspected lesion would need to be sampled to exclude a more diffuse process. You want to examine the paraspinals and remember Willie Sutton. You want to go where the money is. Willie Sutton was a bank robber. It was attributed to him that you want to go where the money is, and that would be the principle underlying this. Sometimes I like to start with the muscles that are weak when I do the needle EMG and go from there. The protocol that's been found to be most sensitive is paraspinals plus six additional muscles, or if you're not testing the paraspinals, eight muscles. If one of the muscles shows neuropathic abnormalities, then study additional muscles, ideally targeting weak muscles to improve diagnostic yield. And polyphasia in the paraspinals is thought to be nonspecific after spine surgery. A couple other pearls, there's no difference between radiculopathy and focal motor neuron disease in EMG, so you want to correlate with clinical findings. The following situations can result in normal needle EMG despite pathology. If a lesion affects only the sensory nerve root or results only in demyelination, or if there's acute pathology, those can result in normal needle EMG examination. And you may not get the textbook presentation of radiculopathy when different fascicles are preferentially affected or spinal stenosis is present. These are from Dr. Preston's textbook on EMG. So finally, some take-home points. Needle EMG tends to be specific for radiculopathy, whereas MRI tends to be sensitive. In this sense, they're very complementary evaluations of the nerve root. MRI tends to pick up structural evaluations while EMG assesses function. And the diagnosis hangs on the needle electrode examination and the weak muscles. Remember Willie Sutton, go where the money is. You always want to make sure that you correlate your EMG and nerve conduction findings with history, physical exam, and imaging. And finally, know this table because this comes up all the time. In a radiculopathy, sensory nerve conduction studies are normal, whereas the paraspinals tend to be abnormal. Whereas in a plexopathy or a mononeuropathy, the sensory nerve conduction studies are abnormal, whereas the paraspinal needle examination is normal. I'd like to thank the following individuals for their help with preparing this presentation. Thank you very much for listening.

radiculopathy

evaluation

anatomy

nerve roots

electrodiagnostic testing