Musings on Pain – a dialogue between the brain and the foot

This is a conversation between a brain and a foot. The foot has been a problem for some time now, years even.

The foot was injured at a railway station early one winter’s morning before the sun had appeared. In the distance I could see the usual people waiting on the platform, sheltering under their hats and behind raised collars. Making my way across the concourse, my shoes were barely gripping the floor. It was clear to see that others had skidded in their haste. The rain had only just stopped.

Although it is a foot that hurts, it is not a foot that hurts. What does that mean? Regular readers will remember that pain is a brain experience 100% of the time. The pain is a response by the brain to a perceived threat and allocated an anatomical location via the cortical maps. In this sense, the brain is creating the experience like all other conscious experiences and making it real. This is the best biological response that the brain can muster at that moment for that particular situation. So, although the foot hurts, the foot doesn’t hurt, it is the brain telling you that you need to do something with the foot by making it hurt. Via the brain. Mmm. See Lorimer Moseley talking below:

 

Pain mechanisms (2)

Keith Smart has been looking at a mechanisms-based approach to pain. As you may recall from the first piece on pain mechanisms and previous writings, I am a proponent of the view that we should be thinking about pain mechanisms. There are significant advantages to elucidating the underpinning physiological and pathology including understanding the patient’s description of their experience and to be able to focus treatment upon the mechanism(s) for more successful outcomes. Below are the papers by Keith Smart and others who have looked at pain mechanisms.

RS www.specialistpainphysio.com

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Clin J Pain. 2011 Oct;27(8):655-63. doi: 10.1097/AJP.0b013e318215f16a.

The Discriminative validity of “nociceptive,” “peripheral neuropathic,” and “central sensitization” as mechanisms-based classifications of musculoskeletal pain.

Source

St Vincent’s University Hospital, Elm Park, Dublin, Ireland. k.smart@ucd.ie

Abstract

OBJECTIVES:

Empirical evidence of discriminative validity is required to justify the use of mechanisms-based classifications of musculoskeletal pain in clinical practice. The purpose of this study was to evaluate the discriminative validity of mechanisms-based classifications of pain by identifying discriminatory clusters of clinical criteria predictive of “nociceptive,” “peripheral neuropathic,” and “central sensitization” pain in patients with low back (± leg) pain disorders.

METHODS:

This study was a cross-sectional, between-patients design using the extreme-groups method. Four hundred sixty-four patients with low back (± leg) pain were assessed using a standardized assessment protocol. After each assessment, patients’ pain was assigned a mechanisms-based classification. Clinicians then completed a clinical criteria checklist indicating the presence/absence of various clinical criteria.

RESULTS:

Multivariate analyses using binary logistic regression with Bayesian model averaging identified a discriminative cluster of 7, 3, and 4 symptoms and signs predictive of a dominance of “nociceptive,” “peripheral neuropathic,” and “central sensitization” pain, respectively. Each cluster was found to have high levels of classification accuracy (sensitivity, specificity, positive/negative predictive values, positive/negative likelihood ratios).

DISCUSSION:

By identifying a discriminatory cluster of symptoms and signs predictive of “nociceptive,” “peripheral neuropathic,” and “central” pain, this study provides some preliminary discriminative validity evidence for mechanisms-based classifications of musculoskeletal pain. Classification system validation requires the accumulation of validity evidence before their use in clinical practice can be recommended. Further studies are required to evaluate the construct and criterion validity of mechanisms-based classifications of musculoskeletal pain.

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J Man Manip Ther. 2010 Jun;18(2):102-10.

The reliability of clinical judgments and criteria associated with mechanisms-based classifications of pain in patients with low back pain disorders: a preliminary reliability study.

Source

UCD School of Public Health, Physiotherapy and Population Science, University College Dublin, Ireland.

Abstract

Mechanisms-based classifications of pain have been advocated for their potential to aid understanding of clinical presentations of pain and improve clinical outcomes. However, the reliability of mechanisms-based classifications of pain and the clinical criteria upon which such classifications are based are not known. The purpose of this investigation was to assess the inter- and intra-examiner reliability of clinical judgments associated with: (i) mechanisms-based classifications of pain; and (ii) the identification and interpretation of individual symptoms and signs from a Delphi-derived expert consensus list of clinical criteria associated with mechanisms-based classifications of pain in patients with low back (±leg) pain disorders. The inter- and intra-examiner reliability of an examination protocol performed by two physiotherapists on two separate cohorts of 40 patients was assessed. Data were analysed using kappa and percentage of agreement values. Inter- and intra-examiner agreement associated with clinicians’ mechanisms-based classifications of low back (±leg) pain was ‘substantial’ (kappa  = 0.77; 95% confidence interval (CI): 0.57-0.96; % agreement  = 87.5) and ‘almost perfect’ (kappa  = 0.96; 95% CI: 0.92-1.00; % agreement = 92.5), respectively. Sixty-eight and 95% of items on the clinical criteria checklist demonstrated clinically acceptable (kappa ⩾ 0.61 or % agreement ⩾ 80%) inter- and intra-examiner reliability, respectively. The results of this study provide preliminary evidence supporting the reliability of clinical judgments associated with mechanisms-based classifications of pain in patients with low back (±leg) pain disorders. The reliability of mechanisms-based classifications of pain should be investigated using larger samples of patients and multiple independent examiners.

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Man Ther. 2011 Nov 8. [Epub ahead of print]

Self-reported pain severity, quality of life, disability, anxiety and depression in patients classified with ‘nociceptive’, ‘peripheral neuropathic’ and ‘central sensitisation’ pain. The discriminant validity of mechanisms-based classifications of low back (±leg) pain.

Source

St Vincent’s University Hospital, Elm Park, Dublin 4, Ireland.

Abstract

Evidence of validity is required to support the use of mechanisms-based classifications of pain clinically. The purpose of this study was to evaluate the discriminant validity of ‘nociceptive’ (NP), ‘peripheral neuropathic’ (PNP) and ‘central sensitisation’ (CSP) as mechanisms-based classifications of pain in patients with low back (±leg) pain by evaluating the extent to which patients classified in this way differ from one another according to health measures associated with various dimensions of pain. This study employed a cross-sectional, between-subjects design. Four hundred and sixty-four patients with low back (±leg) pain were assessed using a standardised assessment protocol. Clinicians classified each patient’s pain using a mechanisms-based classification approach. Patients completed a number of self-report measures associated with pain severity, health-related quality of life, functional disability, anxiety and depression. Discriminant validity was evaluated using a multivariate analysis of variance. There was a statistically significant difference between pain classifications on the combined self-report measures, (p = .001; Pillai’s Trace = .33; partial eta squared = .16). Patients classified with CSP (n = 106) reported significantly more severe pain, poorer general health-related quality of life, and greater levels of back pain-related disability, depression and anxiety compared to those classified with PNP (n = 102) and NP (n = 256). A similar pattern was found in patients with PNP compared to NP. Mechanisms-based pain classifications may reflect meaningful differences in attributes underlying the multidimensionality of pain. Further studies are required to evaluate the construct and criterion validity of mechanisms-based classifications of musculoskeletal pain.

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Pain. 2011 Jul;152(7):1511-6. Epub 2011 Mar 10.

Identifying neuropathic back and leg pain: a cross-sectional study.

Source

School of Rehabilitation Sciences, Faculty of Health and Social Care Sciences, St. George’s University of London/Kingston University, Cranmer Terrace, London SW17 0RE, UK. I.Beith@sgul.kingston.ac.uk

Abstract

Low back pain is a widespread debilitating problem with a lifetime prevalence of 80%, with the underlying pain mechanism unknown in approximately 90% of cases. We used the painDETECT neuropathic pain screening questionnaire to identify likely pain mechanisms in 343 patients with low back pain with or without leg pain in southeastern England referred for physiotherapy. We related the identified possible pain mechanisms nociceptive, unclear, and neuropathic to standardised measures of pain severity (Numeric Rating Scale), disability (Roland Morris Low Back Pain Disability Questionnaire), anxiety and depression (Hospital Anxiety and Depression Scale), and quality of life (Short Form 36 Health Survey Questionnaire Version 2). In addition, we investigated any relationship between these possible pain mechanisms and leg pain, passive straight leg raise, and magnetic resonance imaging evidence confirming or eliminating nerve root compression. A total of 59% of participants (n=204) reported likely nociceptive pain, 25% (n=85) unclear, and 16% (n=54) possible neuropathic pain. The possible neuropathic pain group reported significantly higher pain, disability, anxiety, and depression, reduced quality of life and passive straight leg raise compared to the other pain groups (P<.05). A total of 96% of participants with possible neuropathic pain reported pain radiating to the leg (76% below the knee); however, leg pain was still more common in patients with nociceptive pain, suggesting that leg pain is sensitive to, but not specific to, possible neuropathic pain. No relationship was demonstrated between possible neuropathic pain and evidence for or absence of nerve root compression on magnetic resonance imaging scans. These findings suggest possible neuropathic pain is less common in low back pain patients referred through primary care and clarifies the usefulness of clinical tests for identifying possible neuropathic pain.

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J Pain. 2011 Oct;12(10):1080-7. Epub 2011 Jul 23.

The neuropathic components of chronic low back pain: a prospective multicenter study using the DN4 Questionnaire.

Source

INSERM U 987, Centre d’Evaluation et de Traitement de la Douleur, Hôpital Ambroise Paré, APHP, Boulogne-Billancourt, France. nadine.attal@apr.aphp.fr

Abstract

The present study investigated the neuropathic components of chronic low back pain (LBP) in patients with and without lower limb pain using the DN4 questionnaire and confirmed its psychometric properties. Patients (n = 132) from 11 French multidisciplinary pain or rheumatology centers were classified by a first investigator into 4 groups derived from the Quebec Task Force Classification of Spinal Disorders (QTFSD): group 1 (pain restricted to the lumbar area); group 2 (pain radiating proximally); group 3 (pain radiating below the knee without neurologic signs); and group 4 (pain radiating towards the foot in a dermatomal distribution, with neurological signs, corresponding to typical radiculopathy). A second investigator applied the DN4 questionnaire to the lower limb (groups 2 to 4) and lower back. A comparison of groups 1 and 4 confirmed the psychometric properties of DN4 (sensitivity 80%; specificity 92%, for a cutoff of 4/10, similar to other neuropathic conditions). In the lower limb, the proportion of patients with neuropathic pain (NP) was related to the distality of pain radiation (15, 39, and 80% in groups 2, 3 and 4, respectively; P < .0001). In the lower back, the proportion of patients with NP was higher for patients with typical radicular pain compared with the other groups (P = .006). Thus, typical radiculopathy has similar characteristics as other neuropathic conditions and is confirmed as the commonest neuropathic syndrome in LBP patients. The observation that neuropathic and nociceptive components of LBP vary in the back and lower limb probably accounts for the discrepancies of reported prevalence rates of NP in LBP. As this study was essentially based on a questionnaire, future studies combining standard clinical sensory testing, specific questionnaires, and more objective assessment of the sensory lesion are now required to further investigate the neuropathic component of chronic LBP. PERSPECTIVE: This study confirms the psychometric properties of the DN4 questionnaire to assess neuropathic pain in patients with low back pain. Neuropathic mechanisms largely contribute to pain in the lower limb as compared to the back, but neuropathic pain is not restricted to typical radiculopathy. This may have significant implications for the choice of treatment strategy in these patients.