Diagnosis of Neck and Upper Extremity Pain
Patients with neck and upper extremity pain and underlying multilevel cervical disc disease present special problems in the diagnosis and management of the primary pain generator. These lesions are routinely diagnosed on x-ray, computed tomography (CT), and magnetic resonance imaging (MRI) as degenerative, and not usually considered as a legitimate source for the patient’s pain complaints, resulting in undertreatment and delay in improving the baseline pain control.
The flexor carpi radialis median nerve H-reflex (FCR-HR) study1 evaluates neurologic pathways encompassing the C6 and C7 nerve roots, and the median nerve F-wave (MNF)1 assesses those pathways involving nerve roots C6, C7, C8, and T1. Their assessment of the inherent functional impact of lesions affecting these roots would help clinicians resolve the primary source of the patient’s pain. This would then permit a focused and more directed approach to definitive management. With the above neuroanatomy in mind, they are particularly suited for this task, as both are mediated in part or in whole by the C6 and C7 nerve roots, which exit the cervical spine at the C5-6 and C6-7 levels, respectively. Hence, a delayed or impersistent (less than 8 of 10) response would indicate the presence of a lesion at either spinal segmental level.
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Note that when ordering an electromyography/nerve conduction velocity (EMG/NCV) study, you should specifically request that these two studies be performed, as some electromyographers may not routinely include them.
Neurophysiology of FCR-HR
Akin to the biceps deep tendon reflex (C5, C6), the median nerve H-reflex is monosynaptic. This begins as the operator applies submaximal stimulation to selectively stimulate the Ia median nerve fibers (Ia-subtype of sensory nerve fiber, within muscle fiber’s spindle that relays information regarding changes in velocity of muscle stretch), resulting in the initial sensory afferent signal to the dorsal root ganglion. The signal then enters the spinal cord’s dorsal horn, synapses centrally to the anterior horn cell, and is then propagated efferently via the α-motor axon to the flexor carpi radialis. This results in the very typical and easily recognizable triphasic waveform of the H-reflex (see Figure 1).
As a side note, until you have your actual test results in hand, simply perform the biceps deep tendon reflex bilaterally to clinically screen for pathology at the C5-6 spinal segmental level. Then confirm any abnormality once the H-reflex study has been performed.
In our experience, the side-to-side difference often is subtle and easily missed, so close attention should be paid to any slight and repeatable difference (asymmetry) in your visual assessment of the deep tendon reflexes. Also, if the cord is particularly affected by the lesion, you may actually witness an increased deep tendon reflex response on one side due to irritation of the cord’s upper motor neuronal pool.
Neurophysiology of MNF
The MNF is a variable synaptic response. This begins as the operator applies supramaximal stimulation. However, repeated stimulations are required before an afferent volley arrives at the anterior horn cell at the proper time in order to depolarize the cell. With supramaximal stimulation, essentially the entire nerve is depolarized, resulting in diffusion of the afferent signal to several anterior horn cells. Because different afferent stimuli are arriving at various times and involving different anterior horn cells (chronodispersion), the F-wave morphology will be variable, as will its latency. We will record up to 10 F-wave responses and accept the fastest one (ie, the one with the shortest latency) to determine if it is within normal limits (see Figure 2).
Given that the MNF is mediated via the C6, C7, C8, and T1 nerve roots, to screen clinically for pathology at these spinal segmental levels, you must perform the biceps, brachioradialis, and triceps deep tendon reflexes bilaterally. Then confirm any abnormality once the F-wave study has been completed.
As noted, often the side-to-side difference is subtle, and you must look for any slight and repeatable asymmetry in your visual assessment of the deep tendon reflexes. Also, if the cord is particularly affected, the reflexes actually may be increased.
Although the literature describes the use of the H-reflex and F-wave in the diagnosis of neuropathy and radiculopathy,1-3 we have found them to be of additional value in assessing cervical degenerative discs at the C5-6 and C6-7 levels as potential pain generators.
Sixty-eight patients with neck and upper extremity pain were studied over a 24-month period. All underwent EMG/NCV studies, in which those with median nerve neuropathy above the wrist and abnormal FCR-HR were excluded. Results were then correlated with MNF, EMG paraspinals,4 x-ray, CT, MRI, and clinical findings. Lesions found on imaging included disc degeneration, disc bulge, protrusion, extrusion, listhesis, foraminal narrowing, cord impingement, thecal sac effacement, osteophytic ridging, Modic type I changes, and central canal stenosis.
Figures 3 and 4 illustrate how to perform the techniques.
We found the FCR-HR5 to be abnormal in 63% of patients. In this group, 72% had abnormal FCR-HR correlated with C5-6 and/or C6-7 lesions on x-ray, CT, or MRI. When the abnormal H-reflex was compared with the EMG paraspinal needle study, a 65% correlation was found at the C5-6 and C6-7 levels. In addition, an abnormal MNF was correlated with an abnormal median nerve H-reflex 21% of the time. Incidentally, an abnormal radial nerve F-wave was less helpful, with only a 12% correlation with the abnormal H-reflex.
The FCR-HR study (63%) and the median nerve F-wave (21%) are useful diagnostic tools in the assessment of C5-6 and C6-7 cervical disc disease as a primary pain generator.6 We recommend their routine use in the evaluation of patients with neck and upper extremity pain who present with multilevel cervical disc disease.