Critical Appraisal for a Reference-Standard Validity Study
P: For patients with chronic low back pain, with varying levels of distress,
I: can the centralization phenomenon
C: as compared to discography results
O: provide diagnostic power for discogenic pain
Vincent Gutierrez, PT, MPT, cert. MDT
Ovidsp with keyword terms “low back pain and centralization and specificity and sensitivity”. 44 citations were found between the years 2004 and 2014.
Date of Search: January 21,2014
Re-evaluation date: January 25, 2014
Laslett M, Oberg B, Aprill C, McDonald B. Centralization as a predictor of provocation discography results in chronic low back pain, and the influence of disability and distress on diagnostic power. Spine Journal 2005;5:370-380.
This validation study has two purposes. The first is to investigate the predictive value of the centralization phenomenon (CP) in relation to provocation discography, which is the only reference standard available for discogenic pain. The second is to investigate the role of distress and disability with regards to the predictive value of the centralization phenomenon in relation to provocation discography.
The inclusion criteria were patients with persistent low back pain (LBP), with or without lower extremity (LE) symptoms, whom were referred to a private radiology practice. Patients were excluded for the following reasons: a normal magnetic resonance imaging (MRI) assessment, severe degeneration associated with spondylolisthesis, and if the discography was contraindicated or a referral ruled out discography. The patients that were included were assessed consecutively.
Prior to the evaluation by a physical therapist, the patient completed a visual analog scale (VAS) for pain and the Roland-Morris Disability Questionnaire (RMDQ). The Zung Depression Index (ZDI), Modified Somatic Perception Questionnaire (MSPQ) and the Distress Risk Assessment Method (DRAM) were also completed prior to the physical therapy (PT) evaluation. The evaluation was performed prior to the discography and the physician performing the discography was blinded to the therapist’s results. The therapist was blinded to the results of the subjective outcome measures.
The physical evaluation consisted of a McKenzie evaluation. The exam required 30-60 minutes and also included sacro-iliac joint (SIJ) provocation tests. Centralization or peripheralization was noted and at this point the examination was terminated.
Discography was performed using standard technique and the patient was required to report pain in at least one disc, without pain at an adjacent disc in order to receive a positive test result.
One hundred eighteen patients participated in the PT evaluation and discography. One hundred seven patients were included in the initial analysis. Of the 107 patients, 69 received a full PT evaluation, 21 received a partial evaluation and 17 did not receive an evaluation. Of the above, the physical therapist offered an opinion regarding CP for 83 patients.
The authors utilized the only reference standard studied, provocation discography, in order to determine if CP is predictive of discogenic pain. The physician was blinded to the physical therapists’ evaluation and the physical therapist was blinded to the patients subjective outcome measures. Not all patients received both the PT evaluation and discography.
The confidence interval was 95%. For non-distressed patients, the following statistical measures were calculated: sensitivity of 37%, specificity of 100%, positive likelihood ratio (LR+) and negative likelihood ratio (LR-) were incalculable due to a specificity of 100%. For distressed patients, the following statistical measures were calculated: sensitivity of 45%, specificity of 89%, LR+ of 4.1, and LR- of 0.61. For not severely disabled patients, the following statistical measures were calculated: sensitivity of 35%, specificity of 100%, LR+ and LR- are incalculable due to 100% specificity. For severely disabled persons, the following statistical measures were calculated: sensitivity of 46%, specificity of 80%, LR+ of 3.2 and LR- of 0.63
Performing a McKenzie evaluation in order to determine the presence of CP is a good test for determining a positive discography, especially in patients without severe disability or distress. The presence of CP improves the pre-test probability to post-test probability of positive discography from 39% to greater than 75% in patients with severe disability or distress. CP is a strong predictor of positive discography in patients without severe distress or disability.