Research Review By Dr. Brynne Stainsby©

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Date Posted:

August 2016

Study Title:

Exploration of sensory impairments associated with C6 and C7 radiculopathies

Authors:

Rainville J, Laxer E, Keel J et al.

Author's Affiliations:

Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, MA, USA; New England Baptist Hospital, 125 Parker Hill Avenue, Boston, USA; OrthoCarolina Spine Center, Charlotte, NC, USA; Seton Medical Center, Austin, TX, USA; Department of Orthopedic Surgery, Tufts Medical School, Boston, USA.

Publication Information:

The Spine Journal 2016; 16: 49-54.

Background Information:

Approximately 4% of the population will experience symptoms of a cervical radiculopathy, consisting of pain, motor weakness and deep tendon reflex changes in the upper limb (1, 2). Of these patients, 33% have been found to have impaired dermatomal sensation (1).

Typically, sensation in the affected arm is evaluated during the physical examination of these patients, such that the clinician assesses subjective differences in the patient’s perception of a stimulus between the affected and unaffected arm. Currently, there is a lack of consensus regarding the accuracy of traditional dermatome maps in general, particularly with respect to overlap between the C6 and C7 dermatomes (9, 10, 13). If this is correct, there may be limited value in the sensory examination to differentiate between C6 and C7 radiculopathies. As such, the aim of this study was to compare sensory deficits in subjects with C6 and C7 radiculopathies, and determine the value of sensory testing for differentiating between them.

Pertinent Results:

Originally, 122 subjects with symptoms that suggested cervical radiculopathy were recruited to complete this study. Fifty-two were excluded, and a total of 30 subjects with C6 radiculopathy and 40 subjects with C7 radiculopathy were included. In these 70 subjects, motor and reflex findings were characteristic of the respective radiculopathy.

When findings were mapped, 83% of subjects with C6 and 78% of subjects with C7 radiculopathies had at least one area of sensory impairment on a grid of the forearm and hand. In general, subjects reported sensory impairment in distal forearms and in the fingers, and most had sensory impairments that extended into multiple grid areas.

For those with C6 radiculopathy, sensory impairments were found most often in the distal radial forearm, palmar and dorsal thumb and palmar index finger. For those with C7 radiculopathies, sensory impairments were most commonly found in the palmar and dorsal thumb and index finger and the palmar middle finger.

Frequencies were calculated for each grid region, and statistical significance between the two radiculopathies was found only in the distal radial aspect of the dorsal forearm. In this region, there was a higher association of C6 radiculopathy (p = 0.02).

Clinical Application & Conclusions:

This study demonstrated near complete overlap in areas of sensory impairments in subjects with C6 and C7 radiculopathies, and supports the concept that C6 and C7 innervate similar areas in the distal forearm (13). As clinicians, it is important to recognize that although sensation is typically tested in specific dermatomes, this may not clearly represent a radiculopathy. These results emphasize the importance of establishing a clinical picture when assessing patients, and not relying solely on one finding. In these subjects, radiculopathy was established by motor, reflex and imaging findings, and the authors suggest that hard neurological findings may be more valuable than sensory impairments when localizing radiculopathy.

This study also found that the most common areas of sensory impairment are in the distal aspects of the dermatomes, particularly the distal radial forearm, and the palmar aspects of the thumb, index and middle fingers. It may optimize efficiency in examination to focus sensory testing in these areas, particularly the distal radial forearm in those with suspected C6 radiculopathy.

Study Methods:

Power analysis performed prior to the study required a minimum of 27 subjects with each of C6 and C7 radiculopathy to be recruited. Subjects between the ages of 18-90 with suspected cervical radiculopathy were recruited by 6 physiatrists and 5 orthopaedic surgeons. Relevant exclusion criteria included:
  • Neurologic diseases
  • Distal compressive mononeuropathy
  • Bilateral arm symptoms
Following patient recruitment, demographic and clinical information was obtained. A systemic sensory examination was performed, prior to the motor and sensory examination and review of imaging. As such, patient exclusion also occurred based on imaging findings such as lack of CT or MRI findings to confirm radiculopathy, or the presence of stenosis or other diagnoses that could have been the cause of the symptoms.

The sensory examination consisted of pinprick testing of the affected limb and subjects were asked to report areas of diminished or absent sensation relative to the unaffected limb. Areas of sensory impairment were then recorded on drawings of the anterior and posterior upper limb.

The testing proceeded from distal to proximal by applying pinpricks at 1 cm intervals through the digits and hand (dorsal followed by palmar) to the wrist crease. In the forearm, the same procedure was applied with pinpricks at 2-3 cm intervals along four lines:
  1. Mid-dorsal wrist to the posterior elbow
  2. Ulnar aspect of the wrist to the medial epicondyle
  3. Centre of the anterior wrist to the centre of the antecubital fossa
  4. Radial aspect of the wrist to the lateral epicondyle
Following the sensory examination, manual muscle testing of the upper limb myotomes was performed and recorded as normal (equal to the asymptomatic side) or impaired if less than the asymptomatic side. Biceps, brachioradialis and triceps reflexes were tests and recorded as normal (equal to the asymptomatic side) or impaired if diminished or absent compared to the asymptomatic side.

Sensory impairment findings were translated from the drawings into a grid with 36 distinct areas for analysis. Results were analyzed to calculate the frequency of findings in each grid area in the symptomatic arm and frequencies were compared for C6 and C7 radiculopathies using a chi-square test.

Study Strengths / Weaknesses:

Strengths:
  • The authors recruited subjects based on clinical presentation and performed a systematic sensory examination prior to performing other tests or reviewing images in order to reduce potential test review bias.
  • This study excluded any patients with concurrent anatomic findings or neurological comorbidities (including multiple nerve root involvement).
  • Subjects in this study were required to have an asymptomatic limb to ensure a reference standard that was individualized for each subject.
Weaknesses:
  • The primary limitation of the study is the lack of power to determine statistical significance.
  • Despite efforts to reduce bias, the assessors in this study were clinicians with extensive experience with cervical radiculopathies and may have introduced bias into their assessment. With that said, it must be considered that because the assessors had such extensive experience with radiculopathy, their bias would likely have caused them to expect findings to appear in the “traditional/dermatomal” pattern, but that was not the case. As such, if present, this bias may not have affected the study results.
  • This study asked that subjects report diminished or absent sensation, but did not account for altered sensation. It is possible that this finding may have represented a different pattern which could be analyzed in future studies.
  • It is also important to note that this study was performed using participants recruited specifically based on their sensory impairments from secondary care centers (spine and orthopedic practices), which affects the external validity (generalizability) of these results in primary care settings.
  • Lastly, it is important to acknowledge that this study attempted to evaluate sensory impairments in isolation. While interesting, it is unlikely that we would rely solely on this finding in practice.

Additional References:

  1. Radhakrishnan K, Litchy W, O’Fallon M et al. Epidemiology of cervical radiculopathy: a population based study from Rochester, Minnesota. Brain 1994; 117: 325–35.
  2. Salemi G, Savettieri G, Meneghini F et al. Prevalence of cervical spondylotic radiculopathy: a door-to-door survey in a Sicilian municipality. Acta Neurol Scand 1996; 93: 184–8.
  3. Yoss R, Corbin K, MacCarty C et al. Significance of symptoms and signs in localization of involved root in cervical disk protrusion. Neurology 1957; 7: 673–83.
  4. Wainner R, Fritz J, Irrgang J et al. Reliability and diagnostic accuracy of the clinical examination and patient self-report measures for cervical radiculopathy. Spine 2003; 28: 52–62.
  5. Rainville J, Noto DJ, Jouve C et al. Assessment of forearm pronation strength in C6 and C7 radiculopathies. Spine 2007; 32: 72–5.
  6. Keegan JJ. Dermatome hypalgesia associated with herniation of intervertebral disk. Arch Neurol Psychiatry 1943; 50: 67–83.
  7. Poletti CE. C2 and C3 pain dermatomes in man. Cephalalgia 1991; 11: 155–9.
  8. Wolff M, Levine L. Cervical radiculopathies: conservative approaches to management. Phys Med Rehabil Clin N Am 2002; 13: 589–608.
  9. Foerster O. The dermatomes in man. Brain 1933; 56: 1–39.
  10. Keegan JJ. Relations of nerve roots to abnormalities of the lumbar and cervical portions of the spine. Arch Surg 1947; 55: 246–70.
  11. Inouye Y, Buchthal F. Segmental sensory innervation determined by potentials recorded from cervical spinal nerves. Brain 1977; 100: 731–48.
  12. Nitta H, Tajima T, Sugiyama H et al. Study on dermatomes by means of selective lumbar spinal nerve block. Spine 1993; 18: 1782–6.
  13. Lee MWL, McPhee RW, Stringer MD. An evidence-based approach to human dermatomes. Clin Anat 2008; 21: 363–73.
  14. Suri P, Hunter DJ, Katz JN, et al. Bias in the physical examination of patients with lumbar radiculopathy. BMC Musculoskelet Disord 2010; 11: 275.
  15. Vernon H, Mior S. The Neck Disability Index: a study of reliability and validity. J Manipulative Physiol Ther 1991; 14: 409–15.
  16. Davis L, Martin J, Goldstein SL. Sensory changes with herniated nucleus pulposus. J Neurosurg 1952; 9: 133–8.