The journal of pain : official journal of the American Pain Society
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Myofascial pain syndrome (MPS) is an important clinical condition characterized by chronic muscle pain and a myofascial trigger point (MTrP) located in a taut band (TB). However, its pathogenic mechanism is still unclear. We developed an animal model relevant to conditions of MPS, and analyzed the mechanism of the muscle pain in this model. We applied eccentric contraction (EC) to a rat's gastrocnemius muscle (GM) for 2 weeks, and examined the mechanical withdrawal thresholds, histological changes, and expressions and contents of nerve growth factor (NGF). The mechanical withdrawal threshold decreased significantly at the next day of first EC and continued up to 9 days after EC. TBs were palpable at 3 to 8 days after initiation of EC. In EC animals, necrotic and regenerating muscle cells were found significantly more than in control animals. In EC animals, NGF expressions in regenerating muscle cells and NGF contents of GM were significantly higher than control animals. Administration of NGF receptor (TrkA) inhibitor K252a showed significant suppression of mechanical hyperalgesia in EC animals. Repeated EC induced persistent mechanical muscle hyperalgesia associated with TB. NGF expressed in regenerating muscle cells may have an important role in persistent mechanical muscle hyperalgesia which might be relevant to pathogenesis of MPS. ⋯ The present study shows that NGF expressed in regenerating muscle cells is involved in persistent muscular mechanical hyperalgesia. NGF-TrkA signaling in primary muscle afferent neurons may be one of the most important and promising targets for MPS.
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Multicenter Study
The neuropathic components of chronic low back pain: a prospective multicenter study using the DN4 Questionnaire.
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. ⋯ 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.
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Randomized Controlled Trial Multicenter Study
Early improvement in pain predicts pain response at endpoint in patients with fibromyalgia.
An unanswered, but clinically important question is whether there are early indicators that a patient might respond to duloxetine treatment for fibromyalgia pain. To address this question, pooled data from 4 double-blind, placebo-controlled trials in duloxetine-treated patients (N = 797) with primary fibromyalgia as defined by the American College for Rheumatology were analyzed. Classification and Regression Tree (CART) analysis was used to determine what level of early pain improvement as measured by the 24-hour average pain severity question on the Brief Pain Inventory (BPI) best predicted later response. The predictor variables tested were 10, 15, 20, 25, and 30% decrease in BPI 24-hour average pain from baseline to Week 1 and Week 2. The results of the CART analysis showed that for patients with ≥15% improvement in pain at Week 1 and ≥30% improvement at Week 2, the probability of response at 3 months was 75%. For patients with <15% improvement at both Week 1 and Week 2, the probability of not responding at 3 months was 86%. Quantifiable early improvement in pain during the first 2 weeks of treatment with duloxetine was highly predictive of response or nonresponse after 3 months of treatment. ⋯ This article presents early indicators that can highly predict later pain response or nonresponse in fibromyalgia patients treated with duloxetine. The results may aid clinicians to predict the likelihood of response at 3 months within the first 2 weeks of treatment.
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A triad of clinical symptoms, ie, autonomic, motor and sensory dysfunctions, characterizes complex regional pain syndromes (CRPS). Sensory dysfunction comprises sensory loss or spontaneous and stimulus-evoked pain. Furthermore, a disturbance in the body schema may occur. In the present study, patients with CRPS of the upper extremity and healthy controls estimated their hand sizes on the basis of expanded or compressed schematic drawings of hands. In patients with CRPS we found an impairment in accurate hand size estimation; patients estimated their own CRPS-affected hand to be larger than it actually was when measured objectively. Moreover, overestimation correlated significantly with disease duration, neglect score, and increase of two-point-discrimination-thresholds (TPDT) compared to the unaffected hand and to control subjects' estimations. In line with previous functional imaging studies in CRPS patients demonstrating changes in central somatotopic maps, we suggest an involvement of the central nervous system in this disruption of the body schema. Potential cortical areas may be the primary somatosensory and posterior parietal cortices, which have been proposed to play a critical role in integrating visuospatial information. ⋯ CRPS patients perceive their affected hand to be bigger than it is. The magnitude of this overestimation correlates with disease duration, decreased tactile thresholds, and neglect-score. Suggesting a disrupted body schema as the source of this impairment, our findings corroborate the current assumption of a CNS involvement in CRPS.
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Adults who suffer from chronic pain are at increased risk for suicide ideation and attempts, but it is not clear whether adolescents with chronic pain are similarly at elevated risk. This study investigates whether chronic pain is associated with an increase in suicidal ideation/attempts independent of depression in a population sample of adolescents. We analyzed data from the National Longitudinal Study of Adolescent Health, a longitudinal study of a nationally representative sample of adolescents in the United States (N = 9,970). Most chronic pain was related to suicide ideation/attempt both in the last year (odds ratio [OR] 1.3-2.1) and during the subsequent year (OR 1.2-1.8). After controlling for depressive symptoms, headaches (OR = 1.3 last year, OR = 1.2 subsequent year) and muscle aches (OR = 1.3 last year) remained associated with suicide ideation but not suicide attempt. These findings show that chronic pain in adolescence is a risk factor for suicide ideation; this effect is partly but not fully explained by depression. Youth with comorbid depression and chronic pain are at increased risk of thinking about and attempting suicide. Clinicians should be alert to suicide ideation/attempt and comorbid depression in this at-risk population. ⋯ Adolescents who suffer from chronic pain are at increased risk for suicide ideation and attempt. Depressive symptoms account for the link between chronic pain and suicide attempt, but do not completely explain why adolescents with chronic pain show suicide ideation.