Research Review By Dr. Jeff Muir©

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Date Posted:

December 2019

Study Title:

Where do patients with MRI-confirmed single-level radiculopathy experience pain, and what is the clinical interpretability of these pain patterns? A cross-sectional diagnostic accuracy study

Authors:

Albert HB, Hansen JK, Sogaard H & Kent P

Author's Affiliations:

The Modic Clinic, Odense, Denmark; Research Department, Spine Centre of Southern Denmark, Lillebaelt Hospital, Denmark; School of Physiotherapy and Exercise Science, Curtin University, Australia; Department of Sports Science and Clinical Biomechanics, University of Southern Denmark

Publication Information:

Chiropractic & Manual Therapies 2019; 27: 50.

Background Information:

Low back pain (LBP) with radiculopathy has a lifetime prevalence of 5% (1, 2) but accounts for a disproportionately high proportion of expenditures for LBP (3). Appropriate treatment depends largely on proper diagnosis; however, the varying causes of radicular symptoms – somatic, neurogenic and visceral – can complicate diagnosis based on the description of radicular symptoms. Relating radiculopathy to dermatomal patterns is a common diagnostic approach, although it is also known that dermatomes have wide overlap and vary considerably among individuals (4), and there is additional evidence to indicate that radicular pain is not necessarily dermatomal (5-7).

The goals of this study were therefore to identify L4, L5 and S1 radicular pain patterns and determine: 1) whether they were dermatomal; and 2) if the patterns were clinically indicative of the nerve root level involved.

Pertinent Results:

Participants:

The study included 93 patients with an average age of 43.6 years (SD: 9.74), of which 45.2% were female. Radiculopathy duration ranged from 0.5 – 3.0 months; median VAS was 6.0 for low back pain and 4.0 for leg pain.

Nerve root irritation was localized to L4/5 with L5 nerve root irritation in 41.9% of cases, while 58.1% had L4/5 injury with S1 nerve root irritation.

Pain Patterns:

L5 Nerve Root: L5 pain distribution radiated in a longitudinal pattern from the centre of the lumbar spine, diagonally across the gluteal region, extending posterolaterally along the thigh and calf to the ankle. Pain was additionally reported anterolaterally along the thigh and calf, extending until the dorsum of the foot.

S1 Nerve Root: S1 pain was reported as radiating from the central lumbar area, diagonally along the central gluteal region, posteriorly down the thigh to the calf and ankle.

Clinical Utility of Pain Patterns:

Pain charts were correctly identified by participating clinicians (6 physiotherapists, 6 MDs and 6 DCs with an average of almost 14 years’ experience) as either L5 or S1 nerve root irritation in only 54.4-54.8% of cases (range per clinician: 41.5-64.2%). No significant differences between clinical groups were noted (i.e. prior knowledge of patient-reported pain patterns did not increase the likelihood that pain patterns would be correctly identified). The sensitivity for L5 root identification was 55.6%, specificity was 46.3%, positive likelihood ratio was 1.04 and negative likelihood ratio was 0.96. At the S1 level, sensitivity was 53.7%, specificity was 44.4%, positive likelihood ratio was 1.16 and negative likelihood ratio was 0.85.

On average, the number of clinicians that correctly classified the nerve root level on each patient was 9.7 (out of a possible 18) (SD: 5.0). The classification did not differ across nerve root levels (p = 0.60).

Clinical Application & Conclusions:

The authors conclude that radicular patterns in this cohort only approximate sensory dermatomes. Prior knowledge of the patient-reported radicular pattern also did not improve the likelihood that clinicians could accurately identify the involved nerve root level. As such, they conclude that pain distribution patterns alone do not provide anything more than minimal diagnostic information regarding the involved nerve root. Pain distribution can be interpreted as an indication of radiculopathy but should not be considered an entirely accurate way to identify the specific level involved.

EDITOR’S NOTE: clinicians are often discouraged by studies like this, but I think in some ways these findings simplify our clinical approach a bit. What I mean by that is – stressing about the exact location of pain distribution likely does not result in a higher chance of identifying a specific level, so it remains more important to overtly recognize the symptomatology (ex. pain the low back AND leg), put together the pieces (corresponding reflex, motor or sensory deficiencies) and arrive at an accurate diagnosis (ex. lumbar disc herniation) regardless of the specific level. This doesn’t mean we can’t approximate or guess the level based on the totality of clinical information, but we must recognize that our ability to be reliably accurate in this regard is limited. Luckily, the exact level of disc herniation (for example), rarely changes the overall treatment approach in a meaningful way, right? First-line care for lumbar radiculopathy (including disc herniation) is still conservative management (unless there is progressive neurological deterioration, cauda equina symptoms etc.). If the patient progresses to the requirement of a surgical consult, an MRI will be obtained anyway, which will (hopefully) clarify the exact nature and level of the pathology.

Study Methods:

This was a cross-sectional, diagnostic accuracy study. Two sources of data were used: Part I examined pain patterns using a secondary analysis of baseline data collected during a randomized, controlled clinical trial. Part II examined the clinical utility and discriminative ability of identified pain patterns (this data was prospectively collected).

Pain Patterns:
Patients presenting for treatment between November 2000 and December 2001 and between 18-65 years of age were eligible for inclusion. Specific inclusion criteria included: radicular pain to the knee or more distally in one or both legs; leg pain > 3 on a 10-point VAS scale; and a 2-52 week duration of radicular pain.

Patients from a single-blinded RCT were enrolled into this portion of the study. Following a thorough medical examination, all patients underwent an MRI on the lumbar spine. MRIs were evaluated by a consultant radiologist, blinded to each patient’s clinical characteristics. Intervertebral discs were classified as either normal, bulging, focal protrusion, broad-based protrusion, extrusion or sequestration.

Pain Drawing:
Patients were asked to indicate the distribution of their pain on a pain chart. Each drawing was then scanned into an electronic image to ensure consistency in presentation when analyzed. Pain patterns were determined from these drawings and compared with commonly accepted dermatomal patterns for consistency.

Clinical Utility:
18 clinicians participated in the study: 6 physiotherapists, 6 medical doctors and 6 chiropractors. Each was asked to classify 53 randomly selected individual pain charts from patients with L5 or S1 radiculopathy. Clinicians were blinded to all information save for the reported radicular pattern. Clinicians were divided into 3 groups. Group 1 was not shown the pain charts/drawings and classified patterns based on clinical experience. Group 2 reviewed pain charts for 2 minutes and made a determination based on their knowledge of the pain chart and their clinical experience. Group 3 was able to refer to the pain charts as needed and combine that information with their clinical experience.

Study Strengths / Weaknesses:

Strengths:
  • Multiple clinical professions represented within study.
  • Appropriate comparisons allowed determination of the contribution of pain drawings to radicular pattern identification.
Weaknesses:
  • Radicular symptoms could have been caused by structures other than a compressed nerve root (although MRI imaging was obtained).
  • MRIs were obtained in 2000 and 2001, using an older MRI model, which could contribute to poorer quality imaging.
  • No electrodiagnostic testing (i.e. nerve conduction) was performed, which could contribute to identification of radicular patterns.

Additional References:

  1. Heliovaara M, Makela M, Knekt P, Impivaara O, Aromaa A. Determinants of sciatica and low-back pain. Spine 1991; 16(6): 608–14.
  2. Macaskill P, Walter SD, Irwig L, Franco EL. Assessing the gain in diagnostic performance when combining two diagnostic tests. Stat Med 2002; 21: 2527–46.
  3. Shvartzman L, Weingarten E, Sherry H, Levin S, Persaud A. Cost-effectiveness analysis of extended conservative therapy versus surgical intervention in the management of herniated lumbar intervertebral disc. Spine 1992; 17(2): 176–82.
  4. Mitchell S. The supply of nerves to the skin. Philadelphia Medical Times 1874; 4: 401–3.
  5. Beattie PF, Meyers SP, Stratford P, Millard RW, Hollenberg GM. Associations between patient report of symptoms and anatomic impairment visible on lumbar magnetic resonance imaging. Spine 2000; 25(7): 819–28.
  6. Murphy DR, Hurwitz EL, Gerrard JK, Clary R. Pain patterns and descriptions in patients with radicular pain: does the pain necessarily follow a specific dermatome? Chiro Osteopath 2009; 17:9.
  7. Taylor CS, Coxon AJ, Watson PC, Greenough CG. Do L5 and S1 nerve root compressions produce radicular pain in a dermatomal pattern? Spine 2013; 38(12): 995–8.