The journal of pain : official journal of the American Pain Society
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The widely used Adult Responses to Children's Symptoms measures parental responses to child symptom complaints among youth aged 7 to 18 years with recurrent/chronic pain. Given developmental differences between children and adolescents and the impact of developmental stage on parenting, the factorial validity of the parent-report version of the Adult Responses to Children's Symptoms with a pain-specific stem was examined separately in 743 parents of 281 children (7-11 years) and 462 adolescents (12-18 years) with chronic pain or pain-related chronic illness. Factor structures of the Adult Responses to Children's Symptoms beyond the original 3-factor model were also examined. Exploratory factor analysis with oblique rotation was conducted on a randomly chosen half of the sample of children and adolescents as well as the 2 groups combined to assess underlying factor structure. Confirmatory factor analysis was conducted on the other randomly chosen half of the sample to cross-validate factor structure revealed by exploratory factor analyses and compare it to other model variants. Poor loading and high cross-loading items were removed. A 4-factor model (Protect, Minimize, Monitor, and Distract) for children and the combined (child and adolescent) sample and a 5-factor model (Protect, Minimize, Monitor, Distract, and Solicitousness) for adolescents was superior to the 3-factor model proposed in previous literature. Future research should examine the validity of derived subscales and developmental differences in their relationships with parent and child functioning. ⋯ This article examined developmental differences in the structure of a widely used measure of caregiver responses to chronic pain or pain-related chronic illness in youth. Results suggest that revised structures that differ across developmental groups can be used with youth with a range of clinical pain-related conditions.
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Motor dysfunction in complex regional pain syndrome (CRPS) is often considered a functional movement disorder. Earlier studies in patients with functional movement disorders found evidence of cortical inhibition during explicit but not implicit motor tasks, suggesting active inhibition from other brain areas. In this study, we explored whether active inhibition occurs in CRPS patients. We compared patients with CRPS with 2 control groups: healthy controls matched for age and sex, and patients whose hand was immobilized to treat a scaphoid fracture. We used transcranial magnetic stimulation to measure corticospinal excitability at rest and during motor imagery (explicit motor task) and motor observation (implicit motor task). Motor corticospinal excitation measured at rest and during implicit and explicit motor tasks was similar for CRPS patients and healthy controls. Patients with an immobilized hand showed an absence of motor cortical excitation of the corresponding hemisphere during motor imagery of tasks involving the immobilized hand, but not during motor observation. The normal motor cortical processing during motor imagery and motor observation found in the corresponding hemisphere of CPRS patients suggests that the nature of motor dysfunction in this condition differs from that described in literature for patients with functional paresis or under circumstances of limb immobilization. ⋯ This study shows that the nature of motor dysfunction in CRPS patients differs from that encountered in patients with functional paresis or under circumstances of limb immobilization. This information is important for patients and pain clinicians and could help prevent implementation of therapeutic strategies based on incorrect assumptions.
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Evidence shows involvement of the cerebral cortex in the pathophysiology of cluster headache (CH). Here we investigated cortical excitability in episodic CH patients by using transcranial magnetic stimulation. In 25 patients with episodic CH and 13 healthy subjects we evaluated the motor cortical response to single-pulse (ie, motor threshold, input-output curves, cortical silent period) and paired-pulse (ie, intracortical facilitation, short intracortical inhibition) transcranial magnetic stimulation in both hemispheres. Thirteen patients were evaluated outside bout and the remaining 12 patients inside bout. Our results showed increased slope of the input-output curves after stimulation of both hemispheres in patients outside bout and in the hemisphere contralateral to the headache side in patients inside bout. Increased intracortical facilitation was observed in the hemisphere ipsilateral to the headache side in patients evaluated both outside and inside bout; reduced short intracortical inhibition was observed in patients inside bout ipsilateral to the side of pain. In conclusion, we provide evidence of increased cortical excitability in episodic CH both outside and inside bout, especially in the hemisphere ipsilateral to the side of headache attacks. Our results suggest that an abnormal regulation of cortical excitability could be involved in the pathophysiology of CH. ⋯ We investigated cortical excitability in episodic cluster headache by using transcranial magnetic stimulation, providing evidence of cortical hyperexcitability in patients both inside and outside bout. We suggest that an abnormal state of cortical excitability could be involved in the pathophysiology of the disease.
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Elevated glutamate levels within injured muscle play important roles in muscle pain and hyperalgesia. In this study, we hypothesized that protein kinase C (PKC)-dependent TRPV1 phosphorylation contributes to the muscle mechanical hyperalgesia following activation of Group I metabotropic glutamate receptors (mGlu1/5). Mechanical hyperalgesia induced by (R,S)-3,5-dihydroxyphenylglycine (DHPG), an mGlu1/5 agonist, in the masseter muscle was attenuated by AMG9810, a specific TRPV1 antagonist. AMG9810 also suppressed mechanical hyperalgesia evoked by pharmacologic activation of PKC. DHPG-induced mechanical hyperalgesia was suppressed by pretreatment with a decoy peptide that disrupted interactions between TRPV1 and A-kinase-anchoring protein (AKAP), which facilitates phosphorylation of TRPV1. In dissociated trigeminal ganglia, DHPG upregulated serine phosphorylation of TRPV1 (S800), during which DHPG-induced mechanical hyperalgesia was prominent. The TRPV1 phosphorylation at S800 was suppressed by a PKC inhibitor. Electrophysiologic measurements in trigeminal ganglion neurons demonstrated that TRPV1 sensitivity was enhanced by pretreatment with DHPG, and this was prevented by a PKC inhibitor, but not by a protein kinase A inhibitor. These results suggest that mGlu1/5 activation in masseter afferents invokes phosphorylation of TRPV1 serine residues including S800, and that phosphorylation-induced sensitization of TRPV1 is involved in masseter mechanical hyperalgesia. These data support a role of TRPV1 as an integrator of glutamate receptor signaling in muscle nociceptors. ⋯ This article demonstrates that activation of mGlu1/5 leads to phosphorylation of a specific TRPV1 residue via PKC and AKAP150 in trigeminal sensory neurons and that functional interactions between glutamate receptors and TRPV1 mediate mechanical hyperalgesia in the muscle tissue.