As performed. The clusters are represented by the patterns of questionnaire

As performed. The clusters are represented by the patterns of questionnaire scores (A: adjusted individual mean; B: non-adjusted values), thus showing the typical pathological structure of the respecting group. By using this approach five clusters with distinct symptom profiles could be detected in the cohort. Sensory profiles show remarkable differences in the expression of the symptoms. Subgroup 5 does not show any outstanding symptoms and low prevalence of symptoms in general. doi:10.1371/journal.pone.0068273.gdiscs. It is characterized by a dull and SC-1 web aching quality localized in the back [11,27]. Furthermore, due to the musculoskeletal nature of the pain the muscle is explicitly tender to pressure stimuli [28]. These mechanisms are ideally mirrored by cluster 2 which is dominated by pressure induced pain. Thus, it is likely that these patients suffer of nociceptive pain (painDETECT positive: 4.8 ). Patients who fall into subgroup 1 (22 ) predominantly suffer from “pain attacks” (painDETECT positive: 3.38 ). They express that even the slightest movement of the affected lumbar spine is capable of inducing a very severe, short lasting pain in the back that ceases immediately after seconds. However, in contrast to radicular pain, it is located in the lumbar region. Physiologically, it can be assumed that these attacks are evoked by ectopic discharges emanating from sensitized nerves e.g. innervating facet joints and outer layers of intervertebral discs [12]. Secretion of proinflammatory cytokines and neurotrophins as response to constant pressure in the vicinity of the affected nerve seem to be the critical underlying pathophysiological process [12,29].The effect of cyclic mechanical stress on the production of inflammatory agents may induce a synergistic effect of simultaneous mechanical and chemical irritation of the annulus fibrosus cells on the reactionary production of pain mediators (PGE2) [30]. 223488-57-1 web Subgroups 3 and 4 (together 31 of the entire cohort) are characterized by burning and prickling sensations (painDETECT positive: 25 (cluster 3) and 17.2 (cluster 4)). These symptoms are characteristic for neuropathic pain syndromes [13]. Accordingly these clusters may represent the neuropathic subgroups in axial low back pain. Pathophysiological concepts describe an isochronic occurence of neuropathic and nociceptive components in axial back pain [10]. Normally, intervertebral discs are only sparsely innervated; afferent fibers are exclusively located 23727046 at the outer layer of the annulus fibrosus [12]. This situation changes dramatically if the disc tissue is damaged. Diseased human discs are heavily invaded by blood vessels and small nociceptive nervefibers [31]. Macrophages secrete pro-inflammatory cytokines; in particular TNF-a and other neurotrophins act as growth factors Table 3. Distribution of co-morbidities within symptom-clusters.[29]. Thus, nociceptive fibers start sprouting from the outer part into the inner areas of the disc including the nucleous pulposus. One could hypothesize, that besides nociceptive mechanisms continuous compression of axonal sprouts within diseased discs suffer damage due to compressing forces. As a consequence these damaged afferent fibers in the disc give rise to neuropathic pain mechanisms represented by specific symptoms [8]. Interestingly, patients in subgroup 5 did not indicate distinct sensory abnormalities and scored very low sensory symptom severity despite the fact that the average spontaneous p.As performed. The clusters are represented by the patterns of questionnaire scores (A: adjusted individual mean; B: non-adjusted values), thus showing the typical pathological structure of the respecting group. By using this approach five clusters with distinct symptom profiles could be detected in the cohort. Sensory profiles show remarkable differences in the expression of the symptoms. Subgroup 5 does not show any outstanding symptoms and low prevalence of symptoms in general. doi:10.1371/journal.pone.0068273.gdiscs. It is characterized by a dull and aching quality localized in the back [11,27]. Furthermore, due to the musculoskeletal nature of the pain the muscle is explicitly tender to pressure stimuli [28]. These mechanisms are ideally mirrored by cluster 2 which is dominated by pressure induced pain. Thus, it is likely that these patients suffer of nociceptive pain (painDETECT positive: 4.8 ). Patients who fall into subgroup 1 (22 ) predominantly suffer from “pain attacks” (painDETECT positive: 3.38 ). They express that even the slightest movement of the affected lumbar spine is capable of inducing a very severe, short lasting pain in the back that ceases immediately after seconds. However, in contrast to radicular pain, it is located in the lumbar region. Physiologically, it can be assumed that these attacks are evoked by ectopic discharges emanating from sensitized nerves e.g. innervating facet joints and outer layers of intervertebral discs [12]. Secretion of proinflammatory cytokines and neurotrophins as response to constant pressure in the vicinity of the affected nerve seem to be the critical underlying pathophysiological process [12,29].The effect of cyclic mechanical stress on the production of inflammatory agents may induce a synergistic effect of simultaneous mechanical and chemical irritation of the annulus fibrosus cells on the reactionary production of pain mediators (PGE2) [30]. Subgroups 3 and 4 (together 31 of the entire cohort) are characterized by burning and prickling sensations (painDETECT positive: 25 (cluster 3) and 17.2 (cluster 4)). These symptoms are characteristic for neuropathic pain syndromes [13]. Accordingly these clusters may represent the neuropathic subgroups in axial low back pain. Pathophysiological concepts describe an isochronic occurence of neuropathic and nociceptive components in axial back pain [10]. Normally, intervertebral discs are only sparsely innervated; afferent fibers are exclusively located 23727046 at the outer layer of the annulus fibrosus [12]. This situation changes dramatically if the disc tissue is damaged. Diseased human discs are heavily invaded by blood vessels and small nociceptive nervefibers [31]. Macrophages secrete pro-inflammatory cytokines; in particular TNF-a and other neurotrophins act as growth factors Table 3. Distribution of co-morbidities within symptom-clusters.[29]. Thus, nociceptive fibers start sprouting from the outer part into the inner areas of the disc including the nucleous pulposus. One could hypothesize, that besides nociceptive mechanisms continuous compression of axonal sprouts within diseased discs suffer damage due to compressing forces. As a consequence these damaged afferent fibers in the disc give rise to neuropathic pain mechanisms represented by specific symptoms [8]. Interestingly, patients in subgroup 5 did not indicate distinct sensory abnormalities and scored very low sensory symptom severity despite the fact that the average spontaneous p.