Centralization as a predictor of provocation discography results in chronic low back pain, and the influence of disability and distress on diagnostic power

Abstract

Background context

The “centralization phenomenon” (CP) is the progressive retreat of referred pain towards the spinal midline in response to repeated movement testing (a McKenzie evaluation). A previous study suggested that it may have utility in the clinical diagnosis of discogenic pain and may assist patient selection for discography and specific treatments for disc pain.

Purpose

Estimation of the diagnostic predictive power of centralization and the influence of disability and patient distress on diagnostic performance, using provocation discography as a criterion standard for diagnosis, in chronic low back pain patients.

Study design/setting

This study was a prospective, blinded, concurrent, reference standard-related validity design carried out in a private radiology clinic specializing in diagnosis of chronic spinal pain.

Patient sample

Consecutive patients with persistent low back pain were referred to the study clinic by orthopedists and other medical specialists for interventional radiological diagnostic procedures. Patients were typically disabled and displayed high levels of psychosocial distress. The sample included patients with previous lumbar surgery, and most had unsuccessful conservative therapies previously.

Outcome measures

Diagnosis: results of provocation discography. Index test: The CP. Psychometric evaluation: Roland–Morris, Zung, Modified Somatic Perception questionnaires, Distress Risk Assessment Method, and 100-mm visual analog scales for pain intensity.

Methods

Patients received a single physical therapy examination, followed by lumbar provocation discography. Sensitivity, specificity, and likelihood ratios of the CP were estimated in the group as a whole and in subgroups defined by psychometric measures.

Results

A total of 107 patients received the clinical examination and discography at two or more levels and post-discography computed tomography. Thirty-eight could not tolerate a full physical examination and were excluded from the main analysis. Disability and pain intensity ratings were high, and distress was common. Sensitivity, specificity, and positive likelihood ratios for centralization observed during repeated movement testing for pain distribution and intensity changes were 40%, 94%, and 6.9 respectively. In the presence of severe disability, sensitivity, specificity, and positive likelihood ratios were 46%, 80%, 3.2 and for distress, 45%, 89%, 4.1. In the subgroups with moderate, minimal, or no disability, sensitivity and specificity were 37%, 100% and for no or minimal distress 35%, 100%.

Conclusions

Centralization is highly specific to positive discography but specificity is reduced in the presence of severe disability or psychosocial distress.

Introduction

Most episodes of low back pain (LBP) are benign, self-limiting, and resolve within a few days or weeks. However, approximately one-third of patients report persisting pain and activity limitation 12–30 months after initial presentation to primary care [1], [2]. The intervertebral disc is the most common source of persistent nociception in LBP with at least 39% having internal disc disruption [3]. Approximately 30% of cases have pain mediated by either the sacroiliac joint [4], [5] or zygapophysial joints [6]. It is rare for patients to have more than one source of nociception [7].

Making the diagnosis of primary discogenic pain is not straightforward. Plain radiographs and computed tomography cannot differentiate painful from nonpainful pathology [8], [9]. Magnetic resonance imaging can identify many morphological identities, but most of these are present in asymptomatic individuals [10], [11], [12], [13]. Outer annulus disruptions and high-intensity zones imaged by magnetic resonance imaging correlate with provocation of familiar pain during discography [12], [14], [15], [16], but not all discs that produce pain during discography have abnormal signal intensity, disc contour, or significant signs of degeneration on magnetic resonance imaging [17]. Hydraulic distension of lumbar discs during discography does not normally provoke pain in asymptomatic patients [18], but does provoke familiar LBP in at least one level and is painless at an adjacent level in at least 39% of patients [3].

Provocation discography is the only credible method of directly testing the disc, and is the only reference standard available for validity studies of clinical tests for discogenic pain [19]. Yet there is controversy surrounding its validity. Proponents of discography argue that it is a highly specific test for primary discogenic pain [18], [20], and inter-examiner reliability of discographic findings is acceptable [15]. Others have doubts about its diagnostic and clinical value [21], [22]. Regardless, it remains the de facto standard for confirming the disc as a pain generator in LBP patients [17], [19]. However, not all patients should receive this test because it is invasive and expensive. It has been stated that the key challenge for discographers is to determine how to identify those patients likely to benefit from this diagnostic test [20].

The physical examination is generally regarded of little value in diagnosis of the tissue source of pain [23], or classifying back pain patients into subgroups that respond differently to different treatments [9], [24]. The only clinical assessment methods potentially capable of identifying LBP of discogenic origin are vibration [25] and centralization or peripheralization of referred pain during a McKenzie assessment of repeated movements [26]. The centralization phenomenon (CP) is the progressive retreat of referred pain towards the midline of the back in response to standardized movement testing during evaluation of the effect of repeated movements on pain location and intensity. Peripheralization is the progressive movement of the pain further from the midline of the back towards the periphery or significant worsening of the most peripheral symptoms [27]. Inter-examiner reliability of the examination for these phenomena is acceptable when carried out by trained examiners [28], [29], but unreliable when carried out by examiners with minimal or no training [30].

What does the CP actually represent with regard to the experience of LBP? McKenzie hypothesized that movement of the internal contents of the intervertebral disc is the mechanism underlying the progressive movement of pain towards or away from the spinal midline [27], [31]. The relationship between these phenomena and discogenic pain has been investigated. In a study of 63 chronic LBP patients, Donelson et al. [26] reported that centralization of pain occurred in 31 (49%) patients during the McKenzie evaluation, of whom 23 (74%) had positive provocation discography. Of 16 patients whose symptoms peripheralized, 11 had positive discography. From these data, it can be calculated that centralization has sensitivity, specificity, and positive likelihood ratios of 0.92, 0.64, and 2.5, respectively, and peripheralization of 0.69, 0.64, and 1.9, respectively. Collectively these two signs have sensitivity, specificity, and positive likelihood ratios of 0.92, 0.52, and 1.96, respectively [32]. Although Donelson et al. describe the phenomena in detail, it is unclear whether the physical therapy examiners in his study actually used the definition for determining CP or peripheralization in a formal prospective fashion and consistently among the different examiners.

This report presents the results of a study investigating the predictive value of centralization in relation to provocation discography as the reference standard. The criteria for centralization and peripheralization were consistently applied throughout the study in a prospective fashion. There is abundant evidence that psychosocial and patient distress factors profoundly influence therapeutic outcomes [33], and discogenic back pain patients are more disabled and distressed than other back pain patients [34]. Patient disability and distress appear to be associated with increased reports of pain during discography [35] and discography false-positive rates [21], [36]. In this study we also evaluated the influence of distress and disability dimensions on the diagnostic power of the CP in relation to provocation discography.