Research Review By Dr. Brynne Stainsby©

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Date Posted:

January 2018

Study Title:

The diagnostic accuracy of gluteal trigger points to differentiate radicular from nonradicular low back pain

Authors:

Adelmanesh F, Jalali A, Shirvani A et al.

Author's Affiliations:

The Alan Edwards Pain Management Unit, McGill University Health Centre, Montreal General Hospital, Montreal, QC, Canada; Anesthesiology, Tehran University of Medical Sciences, Tehran, Iran; Department of Radiology, Shahid Beheshti University of Medical Sciences, Tehran, Iran; Physical Medicine and Rehabilitation, Iran University of Medical Sciences, Tehran, Iran.

Publication Information:

Clinical Journal of Pain 2016; 32: 666-672.

Background Information:

With nearly 80% of people experiencing low back pain (LBP) throughout their lives, and a one-month prevalence of 37%, LBP is a common and costly cause of pain and disability (1-3). The direct cost of treating LBP in the United States alone is estimated to be over $100 billion annually, though the indirect costs are much, much higher (4).

LBP may be caused by numerous aetiologies, and a clinical diagnosis is important to devising an appropriate patient management strategy (5, 6). Broadly, it has been recommended that LBP be placed into one of three categories: 1) mechanical pain; 2) LBP with radiculopathy (caused by nerve root irritation); or 3) LBP associated with specific cause or pathology (6). Categorical diagnoses will assist clinicians in selecting interventions and should be reached after a careful history and physical examination consisting of valid and reliable clinical tests (6). One of the challenges in distinguishing between mechanical pain and radiculopathy is the potential for active trigger points (TrP) to cause segmental sensitization, which may mimic radicular pain symptoms (7). It is important to note that TrPs may also result from irritated nerves, causing hyperactivity in corresponding myotomes and thus it is possible that radicular pain due to a disc herniation could also result in the occurrence of TrP (7-9).

The aim of this study was to evaluate whether the presence of gluteal TrPs could help to differentiate between radicular and non-radicular LBP.

Pertinent Results:

Patient Characteristics & LBP Classification:
  • A total of 413 patients were screened. 325 finished the study and their results were included in the final analysis (76 were excluded on initial screening and 12 dropped out after signing the consent).
  • 149 (43%) were found to have non-radicular pain, while 185 (57%) had radicular LBP.
  • Of the patients with non-radicular LBP, 79 were female and 61 were male. The average age of these patients was 41.35 +/- 13.96 years. Symptoms began between one week and 14 months prior to their presentation to the clinic.
  • Of the patients with radicular LBP, 98 were female and 87 were male. The average age of these patients was 43.48 +/- 13.08 years. Symptoms began between one week and 34 months prior to their presentation to the clinic.
  • There was no significant difference in male and female distribution between the radicular and non-radicular groups.
Gluteal Trigger Point Evaluation:
  • The gluteal TrP test was positive in 12 patients with non-radicular LBP (8%) and 137 patients with radicular pain (74%).
  • The average gluteal TrP pain threshold was 4.66 +/- 1.28 kg/cm2 for the non-radicular pain group and 4.83 +/- 1.07 kg/cm2 for the radicular pain group.
Clinical Utility of Gluteal Trigger Point Evaluation:
  • The specificity of the gluteal TrP test in the radicular LBP group was 91.4% (95% CI:86.8-96%) and the sensitivity was 74.1% (95% CI 67.7-80.3%).
  • The area under the receiver operating characteristic (ROC) curve was 0.827 (0.781-0.874) – this is a test that illustrates the diagnostic ability of a binary classifier system as its threshold is varied (1.0 is a perfect test, while 0.5 is a useless test).
  • The positive likelihood ratio was 8.62 and the negative likelihood ratio was 0.28.
  • The positive predictive value was 91.9% (95% CI 87.6-96.3%) and the negative predictive value was 72.7% (95% CI 66.1079.3%).

Clinical Application & Conclusions:

This study demonstrated that over 90% of patients with gluteal TrPs were found to have radicular LBP (137 of the 149 that were positive for TrPs). This preliminary study demonstrated high specificity, positive likelihood ratio and positive predictive value; thus, this test may be used to assess radicular pain in those with LBP. It must be noted that there is low sensitivity, and thus the absence of gluteal TrP cannot rule out radicular pain. Astute clinicians should continue to incorporate information from all aspects of their comprehensive patient history and physical examination to arrive at a diagnosis. This study supports the addition of another tool we can use for our LBP patients!

Study Methods:

  • This was a prospective, diagnostic accuracy study carried out from May, 2012 to January, 2013 in accordance with the STARD guidelines for reporting diagnostic accuracy studies (10).
  • Patients referred from hospital departments were evaluated in a tertiary pain clinic within two days of referral. Patients were included in the study if they were 18 years of age or older and experienced pain between the thoracolumbar and lumbosacral junctions. Patients were excluded if they had a history of lumbar spine surgery, rheumatologic disease, fibromyalgia or peripheral neuropathy.
  • A blinded physician with seven years experience assessed eligible participants for the presence of gluteal TrPs using manual palpation. The presence of TrPs was confirmed via the combination of the presence of a taut band, tenderness and pain recognition (all were required). Notably, a twitch response, referred pain and jump sign were not required for the diagnosis of a TrP.
  • If a TrP was identified, pain pressure thresholds were quantified using a pressure algometer.
  • A second clinician (blinded to the TrP testing) then recorded a clinical history and examination. Radicular pain was considered if the patient had a history of LBP radiating to the posterior or lateral thigh, leg or foot; dermatomal sensory changes; changes in deep tendon reflexes; or weakness in any myotome of the lower limb.
  • Within two days of the clinical evaluation, all patients underwent MRI evaluation and images were interpreted by a neuroradiologist and physiatrist (both of whom were blinded to the TrP and clinical assessments).
  • A multidisciplinary panel of experts blinded to the TrP assessment integrated the clinical and imaging findings and assigned patients to radicular or non-radicular LBP classifications. In cases where the findings were unclear or discordant between the clinical and imaging findings, electro-diagnostic studies were recommended and carried out by a physiatrist with 15 years of experience who was blinded to the TrP findings.
  • Mode and median were reported (as data was not normally distributed), and the χ2 test compared male and female frequency in radicular and non-radicular LBP groups. Sensitivity, specificity, positive and negative likelihood ratios, and positive and negative predictive values were calculated with a 2x2 contingency table. True positive was defined as a patient with a positive TrP test and radicular LBP. True negative was defined as a patient with negative TrP test without radicular LBP. A receiver operating characteristic (ROC) curve was plotted using true-positive rate against false-positive rate for the TrP test.

Study Strengths / Weaknesses:

Strengths:
  • This was an interesting study that achieved its calculated sample size.
  • Independent assessment was performed at each evaluation stage.
  • Experienced clinicians performed all assessments.
Weaknesses:
  • The primary limitation of this study relates to the lack of gold standard (nerve block) for comparison and validation of a new clinical test.
  • The authors were not clearly able to describe the additional utility of testing gluteal TrPs when assessing for the presence of radicular pain. They did not indicate any additional value when comparing to clinical history and standard physical examination alone.
  • In this study, only the superolateral region of the gluteal muscles was assessed for the presence of TrPs (isn’t it possible that TrPs could exist in other gluteal regions?).
  • Although possibly suggestive that the presence of gluteal TrPs may indicate radicular LBP, the absence certainly cannot rule out the involvement of nerve roots as a cause of pain. A complete physical examination is required to assist in diagnosis.

Additional References:

  1. Papageorgiou AC, Croft PR, Ferry S et al. Estimating the prevalence of low back pain in the general population. Evidence from the South Manchester Back Pain Survey. Spine 1995; 20: 1889–1894.
  2. Zhang YG, Guo TM, Guo X et al. Clinical diagnosis for discogenic lower back pain. Int J Biol Sci 2009; 5: 647–658.
  3. Karas R, McIntosh G, Hall H et al. The relationship between 
nonorganic signs and centralization of symptoms in the prediction of return to work for patients with lower back pain. Phys Ther 1997; 77: 354–360.
  4. Dagenais S, Tricco AC, Haldeman S. Synthesis of recommendations for the assessment and management of low back pain from recent clinical practice guidelines. Spine J 2010; 10: 514–529.
  5. Zhang Y, Sun Z, Liu J et al. Advances in susceptibility genetics of intervertebral degenerative disc disease. Int J BiolSci. 2008; 4: 283–290.
  6. Chou R, Qaseem A, Snow V et al. Clinical Efficacy Assessment Subcommittee of the American College of Physicians; American College of Physicians; American Pain Society Low Back Pain Guidelines Panel. Diagnosis and treatment of low back pain: a joint clinical practice guideline from the American College of Physicians and the American Pain Society. Ann Intern Med 2007; 147: 478–491.
  7. Gunn CC. Radiculopathic pain: diagnosis, treatment of segmental irritation or sensitization. J Musculoskelet Pain 1997; 5: 119–134.
  8. Fischer AA. New developments in diagnosis of myofascial pain and fibromyalgia. Phys Med Rehabil Clin North Am 1997; 8: 1–27.
  9. Chu J. Dry needling (intramuscular stimulation) in myofascial pain related to lumbosacral radiculopathy. Eur J Phys Med Rehabil 1995; 5: 106–121.
  10. Bossuyt PM, Reitsma JB, Bruns DE et al. The STARD statement for reporting studies of diagnostic accuracy: explanation and elaboration. Clin Chem 2003; 49: 7–18.