Nociceptive versus Neuropathic Chronic Low Back Pain

Distinguishing between nociceptive and neuropathic components in chronic low back pain using behavioural evaluation and sensory examination – free full-text /PMC5329124/ article – Feb 2017

Diagnosis of chronic low back pain (CLBP) is traditionally predicated on identifying underlying pathological or anatomical causes, with treatment outcomes modest at best.

Alternately, it is suggested that identification of underlying pain mechanisms with treatments targeted towards specific pain phenotypes may yield more success.

Differentiation between nociceptive and neuropathic components of CLBP is problematic; evidence suggests that clinicians fail to identify a significant neuropathic component in many CLBP patients.  

The painDETECT questionnaire (PDQ) was specifically developed to identify occult but significant neuropathic components in individuals thought to have predominantly nociceptive pain.

Methods

Using the PDQ, we classified 50 CLBP patients into two distinct groups;

  1. those with predominantly nociceptive pain (Group 1) and
  2. those with a significant neuropathic component (Group 2).

We characterised these two distinct CLBP sub-groups using

  • a) questionnaire-based behavioural evaluation measuring pain-related function and quality of life, pain intensity and psychological well-being and
  • b) sensory examination, using two-point and tactile threshold discrimination.

Objective

We sought to determine if differences in the pain phenotype of each CLBP sub-group would be reflected in sensory and behavioural group profiles.

Results

We report that Group 1 and Group 2 sub-groups demonstrate unique clinical profiles with significant differences in sensory tactile discrimination thresholds and in a wide range of behavioural domains measuring pain intensity, disability and psychological well-being.

Conclusion

We have demonstrated distinct clinical profiles for CLBP patient sub-groups classified by PDQ. Our results give diagnostic confidence in using the PDQ to characterise two distinct pain phenotypes in a heterogeneous CLBP population.

1. Introduction

Heterogeneity in the clinical presentation of Chronic Low Back Pain (CLBP) makes diagnosis and treatment challenging. CLBP treatment pathways are traditionally predicated on identifying pathophysiological causes, which are not possible to identify in 90% of patients (Koes et al., 2006).

The definition and diagnosis of NeuP and its differentiation from nociceptive pain remains controversial. Current IASP guidelines stipulate that a demonstrable lesion or disease of the somatosensory nervous system is necessary in order to arrive at a definitive neuropathic classification (International Association for the Study of Pain, 2016)

Using the current IASP guidelines, only a small percentage of CLBP patients can be classified as ‘neuropathic’ yet, in routine clinical practice, many patients with low back pain present with symptoms that are indicative of a significant neuropathic component (i.e spread of pain, paroxysmal pain, dysaesthesia, allodynia).

However, these patients may either present with no history or confirmatory evidence of a lesion or disease process, with equivocal examination findings and with pain that is not in a ’neuroanotomically plausible’ distribution.

Recent work suggests that clinicians fail to identify significant neuropathic components in a number of people with LBP and that the true incidence of CLBP patients with a significant neuropathic component may be under-diagnosed (Freynhagen et al., 2006)

Patients with occult neuropathic symptoms may therefore be mis-classified as nociceptive, in spite of a seemingly neuropathic symptom profile, or else idiopathic, which allows no indication of underlying pain mechanisms. Worst of all, an idiopathic classification may hint at a pejorative ‘functional’ label to a patient’s symptoms (Cohen et al., 2011).

The PainDETECT questionnaire (PDQ) was specifically developed to identify neuropathic components in patients with CLBP and to differentiate LBP patients with a significant neuropathic component from LBP patients with predominantly nociceptive, mechanical pain without the need for physical examination or confirmatory diagnostic markers.

The PDQ has been shown to have a high

  • sensitivity (85%),
  • specificity, (80%) and
  • positive predictive accuracy (83%) in LBP (Freynhagen et al., 2006).

We therefore chose to use the PDQ to identify two sub-groups within our CLBP population: LBP patients with predominantly nociceptive, mechanical pain (Group 1) and LBP patients with a significant neuropathic component (Group 2).

The primary objective of this study was to characterise these two groups.

4. Discussion

The current study revealed significant differences in sensory examination and behavioural and psychometric data in a group of CLBP patients compared to controls and between neuropathic and non-neuropathic CLBP subgroups, as determined by the PDQ.

CLBP patients reported significantly poorer physical and mental health related quality of life compared to controls across all SF-36 domains, greater psychological distress in all SCL-90-R domains and also greater signs of anxiety (STAI) and depression (CES-D).

CLBP patients also reported significantly increased TTD and 2PD sensory examination thresholds compared to controls.

Group 2 patients reported significantly greater examination day pain using NRS and significantly greater pain (SFMPQ VAS, Sensory Pain Descriptor Scale Present Pain Intensity scale) scores than patients in Group 1.

Group 2 patients experienced significantly poorer physical and mental health related quality of life compared to Group 1 patients (SF-36 domains of Physical functioning, Bodily pain, Vitality, Social functioning, General mental health, Mental component summary and Physical component).

Group 2 patients also exhibited greater signs of depression (CES-D) and psychological distress across SCL-90-R domains (Somatisation, Interpersonal sensitivity, Anxiety, Phobic anxiety, Global severity index and Positive symptom total) compared to Group 1 patients.

TTD examination scores revealed significantly increased sensory thresholds to tactile stimulation in Group 2 compared to Group 1 patients.

4.1. Re-thinking classification of underlying pain mechanisms in CLBP

In this study, we have described CLBP patients with PDQ scores above 18 as having ‘a significant neuropathic component’ to their LBP as recommended by Freynhagen et al. (2006).

Evidence shows that many patients with a diagnosis of non-specific low back pain have a significant neuropathic component to their pain (Freynhagen et al., 2006) and patients within our Group 2 cohort may fail to conform to the current IASP definition of neuropathic pain.

we would suggest that these patients present with a significant neuropathic component to their pain, irrespective of any lesion or pathological status

4.2. Sub-groups of CLBP patients selected by painDETECT reflect different pain phenotypes

We hypothesised that patients with CLBP would exhibit

  • poorer quality of life,
  • greater psychological distress and
  • also exhibit different sensory examination profiles

compared to controls.

In addition, we hypothesised that CLBP patients identified by PDQ as having a significant neuropathic component to their pain (irrespective of lesion or disease status) would complain of

  • greater pain,
  • poorer quality of life,
  • greater psychological distress and
  • also exhibit different sensory examination profiles

compared to Group 1 patients.

Our data supported these hypotheses; group profiles reflect pain phenotypes identified by the PDQ

5. Conclusion

These results not only show significant differences in the clinical profiles of CLBP patients compared to controls, but importantly show that CLBP patients with a significant neuropathic component (Group 2) determined by PDQ, differ in clinical profile to patients with predominantly nociceptive, mechanical symptoms (Group 1).

These data demonstrate that there are distinct differences in the clinical profiles of patients whose diagnosis of neuropathic LBP rests on assessment of symptom profiles, rather than by evidence of a lesion or disease process and whose symptoms may be caused by an underlying maladaptive plasticity of the nervous system.

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