Neuropathic Pain in Ankylosing Spondylitis: A Psychophysics and Brain Imaging Study

Abstract

Objective. To determine whether there is a neuropathic component in ankylosing spondylitis (AS) back pain and to delineate gray matter brain abnormalities associated with AS.Methods. Seventeen patients with back pain secondary to AS who were not receiving biologic agents and 17 age-and sex-matched healthy controls consented to participate in the study and were assessed using the painDETECT instrument (scores of <12 indicating low probability of neuropathic pain) and the McGill Pain Questionnaire. Mechanical and thermal thresholds were determined in all subjects, and brain gray matter was assessed by 3T magnetic resonance imaging.Results. Eleven of the 17 AS patients had pain-DETECT scores of >12. The patients had decreased mechanical and cold sensitivity on the dorsum of their feet but did not have altered pain thresholds. Compared to controls, the AS patients exhibited cortical thinning in the primary somatosensory, insular, anterior cingulate, and anterior mid-cingulate cortices and the supplemental motor area, and increased gray matter volume in the thalamus and putamen. Scores on the painDETECT in AS patients were correlated with decreased gray matter in the primary somatosensory cortex and with increased gray matter in the motor cortex, anterior cingulate cortex, prefrontal cortex, thalamus, and striatum.Conclusion. The present findings indicate that neuropathic pain occurs in AS. Furthermore, abnormal brain gray matter and neural correlates of neuropathic pain are concordant with the clinical picture of AS, which includes sensorimotor and mood deficits as well as neuropathic pain symptoms. These results suggest that back pain in AS is a mixed pain condition that includes a neuropathic pain component.

e association of neuropathic pain and disease activity, functional level, and quality of life in patients with ankylosing spondylitis: a cross-sectional study

“…Dysregulation of central pain processing mechanisms and central sensitization is the underlying pathology of NP. Wu et al (12) showed that higher painDETECT scores in AS patients were found to be correlated with thinning of the primary somatosensory cortex and thickening of the primary motor cortex. The study of Wu et al is valuable since it showed objective findings of central sensitization, which supports the reliability of painDETECT in assessing neuropathic pain.…”

“…There is only one recent study that indicated the presence of NP in AS (12). In that study, correlations of painDETECT scores and abnormal brain gray matter findings were shown.…”

Fatigue in Ankylosing Spondylitis Is Associated With the Brain Networks of Sensory Salience and Attention

“…Patients with AS usually have sensory loss, such as loss of proprioception (44) or decreased mechanothermal sensitivity in the affected dermatome (23). Both pain and sensory loss can cause fatigue and deficits in attention (45,46), which might involve common central mechanisms, either directly affecting brain areas associated with executive functioning (23,47,48), or indirectly regulating the attention functioning by highlevel sensory-attention integration via the secondary somatosensory cortex (43,(49)(50)(51).…”

“…Both pain and sensory loss can cause fatigue and deficits in attention (45,46), which might involve common central mechanisms, either directly affecting brain areas associated with executive functioning (23,47,48), or indirectly regulating the attention functioning by highlevel sensory-attention integration via the secondary somatosensory cortex (43,(49)(50)(51). Our findings (of abnormalities in cortical thickness of frontoparietal executive control networks and of the coupling of cortical thinning in the secondary somatosensory cortex and the contralateral parietal orienting network) support the notion of both the direct and indirect mechanisms mentioned above.…”

“…The fatigue severity measure was not used in the recruitment of patients with AS for the present study; however, most patients (17 of 20) were recruited for a large-scale study of AS (and a component of the criteria defining active AS includes a fatigue score or total back pain score of Ͼ3 [on a 10-point scale]). Seventeen of the patients and their matched controls were also included in our previous study of gray matter abnormalities related to neuropathic pain in AS (23). Other criteria for inclusion were as follows: age 18-60 years, no previous diagnosis of any psychiatric, vascular, endocrine, or neurologic conditions, and no history of any major surgery during the preceding 2 years.…”