Cervical radiculopathy is a common diagnosis with a peak onset in the fifth decade. The most commonly affected nerve root is C7, C6, and C8. The etiology is often compressive, but may arise from noncompressive sources. Patients commonly complain of pain, weakness, numbness, and/or tingling. Examination may reveal sensory or motor disturbance in a dermatomal/myotomal distribution. Neural compression and tension signs may be positive. Diagnostic tests include imaging and electrodiagnostic study. Electrodiagnostic study serves as an extension of the neurologic examination. Electrodiagnostic findings can be useful for patients with atypical symptoms, potential pain-mediated weakness, and nonfocal imaging findings.
Key points
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To properly diagnose cervical radiculopathy, a combination of clinical signs/symptoms, imaging, and electrodiagnostic studies should be used.
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Differential diagnosis must consider various causes of neuropathic and musculoskeletal pain, which may be affecting the extremity.
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Needle electromyography is the most useful electrodiagnostic technique and provides moderate sensitivity in the diagnosis of radiculopathies.
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Appropriate sampling of muscles must be done including paraspinals, if possible, to ensure a diagnostically accurate study.
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Electrodiagnostic findings can be particularly useful for patients with atypical symptoms, potential pain-mediated weakness, and nonfocal imaging findings.
Introduction
Cervical radiculopathy is a common disorder effecting people most often in the fourth and fifth decades of life. Symptoms of pain, numbness, and/or tingling may be mild, but in severe cases, cervical radiculopathy will be associated with motor weakness. Efficient diagnosis can minimize pain and disability and also minimize the direct and indirect costs of care. Treatment of cervical radiculopathy is based on a clear understanding of its natural history, clinical evaluation, diagnostic testing, and therapeutic options for this disorder. This article will provide an overview of the pathophysiology, pertinent anatomy, history/examination findings, and imaging options. It will focus on the electrodiagnosis of cervical radiculopathy. Electrodiagnosis is a critical part of the evaluation of patients presenting with signs and symptoms of neuropathic upper extremity dysfunction, especially when coexisting with neck pain. This article will review developing an appropriate differential diagnosis and choosing appropriate electrodiagnostic techniques with a focus on needle electromyography (EMG).
Introduction
Cervical radiculopathy is a common disorder effecting people most often in the fourth and fifth decades of life. Symptoms of pain, numbness, and/or tingling may be mild, but in severe cases, cervical radiculopathy will be associated with motor weakness. Efficient diagnosis can minimize pain and disability and also minimize the direct and indirect costs of care. Treatment of cervical radiculopathy is based on a clear understanding of its natural history, clinical evaluation, diagnostic testing, and therapeutic options for this disorder. This article will provide an overview of the pathophysiology, pertinent anatomy, history/examination findings, and imaging options. It will focus on the electrodiagnosis of cervical radiculopathy. Electrodiagnosis is a critical part of the evaluation of patients presenting with signs and symptoms of neuropathic upper extremity dysfunction, especially when coexisting with neck pain. This article will review developing an appropriate differential diagnosis and choosing appropriate electrodiagnostic techniques with a focus on needle electromyography (EMG).
Epidemiology
An epidemiologic study of cervical radiculopathy was performed at the Mayo Clinic between 1976 and 1990. Five hundred sixty-one cases were included in this study. This research revealed the following:
Age ranged from 13 to 91 years (332 males, mean age 47.6 ± 13.1 years; 229 females, mean age 48.2 ± 13.8 years)
History of trauma or exertion was found in only 14.8% of cases
Previous history of lumbar radiculopathy was found in 41% of cases
Median duration of symptoms before diagnosis was 15 days
Monoradiculopathy involving nerve root C7 was most common, followed by nerve roots C6, C8, and then C5 in decreasing frequency
Etiology included confirmed disc protrusion (21.9%) and spondylosis, disc, or both (68.4%)
Recurrence over 4.9 years = 31.7%
Surgery was performed in 26% of patients
Ninety percent of patients were asymptomatic or only mildly incapacitated at last follow-up
A more recent study looked at the incidence of cervical radiculopathy in the US military from 2000 to 2009. They found that age (40 years old and above) was the greatest risk factor for cervical radiculopathy, and that female sex, white race, senior military position, and service in the Army or Air Force were also risk factors.
Anatomy
The cervical spine is comprised of 7 vertebrae. The first vertebra (C1, also called the atlas) is a ring-shaped bone without a spinous process. It serves as the point of attachment of the skull to the spine via the occipital condyles articulating with the superior aspect of the C1 vertebra. C1 articulates directly with C2 without the presence of an intervertebral disc. C2 has a bony superior process called the dens, which projects into the ring of the atlas and serves as the axis of rotation.
Facet Joints (Zygapophyseal Joints)
Vertebrae C3 through C7 have posteriorly placed facet joints that serve as points of articulation between the vertebrae. These are paired joints that arise at the junction of the pedicle and the lamina. The superior facets project upward to articulate with the inferior facets of the superior adjacent vertebra. The inferior facets project downward to articulate with the superior facets of the inferior adjacent vertebra. These joints are synovial with a surrounding capsule. The joints are innervated by the medial branch of the dorsal primary ramus of the exiting spinal nerve. The joints provide directional stability and prevent relative translation of 1 vertebra upon another. They lie posterior to the exiting spinal nerve root.
Uncovertebral Joints (Joints of Luschka)
Extending off the lateral surface of the cervical vertebral bodies are small bony projections called uncinate processes. The uncinate process makes contact with the disc and vertebral body above. The points of contact are called uncovertebral joints, and they are located anteromedial to the exiting nerve roots.
Intervertebral Disc
Between cervical vertebrae C2 through C7 is a supporting intervertebral disc. The disc is comprised of 2 layers; the outer layer is called the annulus fibrosis, which is made up of approximately 20 concentric lamellae of orthogonally oriented fibers. The inner layer is called the nucleus pulposis, comprised of 90% water, which desiccates with age. The anterior annulus is reinforced by the anterior longitudinal ligament (ALL), and posteriorly by the posterior longitudinal ligament (PLL). The PLL is not very broad, and accordingly there is greater chance of nucleus pulposis herniation laterally as opposed to centrally.
Spinal Canal
The spinal canal is made up of the consecutive vertebral foramen. In the intervertebral spaces, the canal is protected posteriorly by the ligamentum flavum and anteriorly by the PLL. The spinal canal has its greatest Anterior-Posterior (A-P) diameter in the upper cervical spine between C1 and C3. During maximal cervical spine extension, the canal narrows an additional 2 to 3 mm.
Spinal Motion
The specific motions of each cervical segment have been thoroughly described elsewhere. Broadly speaking, most rotational movement of the head occurs in the upper cervical spine, where flexion and extension occur predominantly in the lower cervical spine. Accordingly, spondylotic disease arises most commonly in the lower cervical spine.
Intervertebral Foramina
The foramina are bordered anteriorly by the vertebral body and disc, and posteriorly by the facet joint. The pedicles form the superior and inferior margins of the foramen. Additionally the uncinate processes are located at the anteromedial margin of the foramen.
Neural Elements
The spinal cord is located within the central canal. There is an enlargement of the cord diameter within the cervical spine from C3 through T2, and in the lumbar spine from L1 to S3. The spinal nerve is comprised of sensory fibers traveling through the dorsal root and motor fibers from the ventral root. The dorsal root ganglia (DRG) are located on the dorsal nerve roots, usually in the intervertebral foramen, just outside the spinal dural layer. The DRG of C4 and C5 are located closer to the spinal cord than the lower roots. The dorsal and ventral roots fuse to form the spinal nerve in the intervertebral foramen. The spinal nerve continues for a few millimeters before it separates into the dorsal and ventral rami. The dorsal rami supply the cervical paraspinals (PSPs) and skin of the back of the neck. The ventral rami form the cervical and brachial plexuses.
The cervical nerve roots exit through the intervertebral foramen above the corresponding cervical vertebral body. For example, the C5 nerve root exits through the C4 to C5 intervertebral foramen. The C8 nerve root exits below the C7 vertebral body and above the T1 vertebral body. Subsequent nerve roots exit below the corresponding vertebral body.
Understanding the anatomy of the exiting spinal nerve with regards to both the innervation of the PSP musculature and position of the DRG is critical in understanding the results of the electrodiagnostic evaluation of cervical radiculopathy.
Etiology
Radiculopathy arises from a process that affects the nerve root. These processes can be divided into compressive and noncompressive causes. The compressive causes include cervical spondylosis and disc herniation.
Compressive Causes
Cervical spondylosis
As the nerve root enters the foramen medially, it lies at the level of the superior articular facet of the inferior vertebrae. Hypertrophy of either the uncovertebral joints or the facets joints may impinge mechanically on an exiting nerve root to cause radiculopathy. The process of degenerative change in these joints is called spondylosis. Degenerative change may also result in bone formation in these areas, producing an osteophyte or hard disc.
Disc herniation
The anatomy of the intervertebral disc has been discussed previously. Circumferential tears in the annulus fibrosis begin to be present around the age of 20 and progress to fraying and splitting of collagen fibers. With the progression of degeneration, there is continued loss of the fluid properties of the nucleus pulposis, which undergoes replacement with fibrous tissue. The combination of intervertebral pressure and degenerative change of the disc can lead to tears in the annulus, which allow for disc bulging and/or prolapse of the nucleus pulposis. This often results in deformation of the DRG. The mechanical deformation (either compression or tension) causes release of substance P, phospholipase 2, and vasoactive intestinal peptide from the nucleus pulposis. This produces a chemical inflammation that is an additional insult to the nerve root on top of any mechanical pressure.
Noncompressive causes
Although less common, noncompressive causes should always be considered. These include demyelination, infection, tumor infiltration, root avulsion, and nerve root infarction. The dorsal and ventral roots may be affected (much more so than in compressive etiologies). Deficits of noncompressive radiculopathies may span multiple myotomes and dermatomes, and may be more complete or dense than are commonly seen in compressive etiologies.
Key history findings
The patient’s history is critical in evaluating a suspected radiculopathy, because there is an extensive differential diagnosis to be considered. Symptoms may develop acutely with an initial episode of neck pain followed by radiation in a dermatomal pattern or weakness in the affected extremity. A herniated disk more often causes acute radiculopathy, while spondylitic narrowing results in a more indolent course. Patients may complain of neck pain, arm pain, chest or shoulder pain, pain in the interscapular region, or pain in the face.
Dermatomal paresthesia or numbness develops in 80% of patients. Subjective weakness is less common than paresthesia. The patient may describe positions that alleviate symptoms, such as rotating the head away from the affected side, and the abducted shoulder sign, in which the patients describe pain relief with the affected shoulder abducted and the hand resting on top of the head.
Some patients may describe a recent history of physical exertion or trauma preceding symptom onset; however, most cases have no readily identifiable causative event.
More concerning complaints that may suggest not only radiculopathy but also myelopathy or infection must also be sought. Lhermitte sign (shock-like paresthesias occurring with neck flexion), difficulty walking, or bowel and bladder symptoms are suggestive of myelopathy or intramedullary pathology. Any history of fever, chills, weight loss, or cancer should raise suspicion for tumor or infection.
Key physical examination findings
The initial physical examination includes observation of the patient, noting the position of the head and neck contours. Atrophy can be detected with more severe or long-standing lesions. Muscle wasting may suggest particular nerve root involvement:
C5 or C6: supra- or infrascapular fossae or deltoid
C7: triceps
C8: thenar eminence
T1: first dorsal interossei
Manual muscle testing has greater specificity than reflex or sensory abnormalities, and might need to be performed repetitively or with the muscle at a mechanical disadvantage to elicit subtle weakness. Severe weakness (<3/5 on the Medical Research Council grade) is less consistent with a single root lesion and should prompt the examiner to search for multilevel pathology. Sensation to light touch, pinprick, and vibration should be assessed. Upper motor neuron signs should also be assessed including Hoffman sign and Babinski response.
Provocative maneuvers such as Spurling maneuver may be performed. This test is performed by extending and rotating the neck to the painful side followed by the application of downward pressure to the head. The test is positive if it reproduces limb pain and/or paresthesia. Neck pain alone does not signify a positive test. The Spurling maneuver has a high specificity but moderate-to-low sensitivity for cervical radiculopathy. A negative test does not rule out radicular pathology.
Related posts:
The Electrodiagnosis of Neuromuscular Disorders
Anatomical, Clinical, and Electrodiagnostic Features of Radial Neuropathies
Electrodiagnosis of Lumbar Radiculopathy
Electrodiagnostic Testing in Lumbosacral Plexopathies
Electrodiagnosis of Myotonic Disorders
Electrodiagnostic Evaluation of Myopathies
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