Pharmacodynamic effect of gabapentin on central nervous system in patients with chronic low back pain: a [99mTc]Tc-ECD SPECT study.

BACKGROUND: Gabapentin is an effective therapeutic alternative for chronic low back pain, indicated in several guidelines for treating neuropathic pain as first-line medication. This study aimed to describe the pharmacodynamics of gabapentin in the central nervous system of patients with chronic low back pain (CLBP) by using single-photon emission CT (SPECT) with [99mTc]Tc-ECD. METHODS: We selected 13 patients with CLBP due to lumbar disc herniation. They underwent SPECT before and after using gabapentin, compared with a SPECT database of healthy volunteers. A second analysis compared regional cerebral blood flow (rCBF) changes between responders and non-responders to gabapentin and the healthy controls. RESULTS: The mean age of patients was 41 years, and the mean pain intensity was 5.92 points, measured by the Numeric Rating Scale. After using gabapentin, SPECT showed an increase of rCBF in the bilateral anterior cingulate gyrus and a decrease of rCBF in periaqueductal gray matter. Non-responder patients with gabapentin showed a post-treatment decrease of rCBF in the paracentral lobule of the brain. CONCLUSIONS: A lack of improvement in some patients with gabapentin may be associated with an activated affective circuit of pain, evidenced by the increase of rCBF of the anterior cingulate cortex. A maladaptive brain state in chronic pain can explain the decrease of rCBF in the default mode network structures. Gabapentin acts directly or indirectly on neurons of periaqueductal gray substance by increasing the pain threshold and decreasing the rCBF of this structure.

Neurobiological substrates of chronic low back pain (CLBP): a brain [99mTc]Tc-ECD SPECT study.

BACKGROUND: Recent neuroimaging studies have demonstrated pathological mechanisms related to cerebral neuroplasticity in chronic low back pain (CLBP). Few studies have compared cerebral changes between patients with and without pain in the absence of an experimentally induced stimulus. We investigated the neurobiological substrates associated with chronic low back pain using [99mTc]Tc-ECD brain SPECT and correlated rCBF findings with the numeric rating scale (NRS) of pain and douleur neuropathique en 4 questions (DN4). Ten healthy control volunteers and fourteen patients with neuropathic CLBP due to lumbar disc herniation underwent cerebral SPECT scans. A quantitative comparison of rCBF findings between patients and controls was made using the Statistical Parametric Mapping (SPM), revealing clusters of voxels with a significant increase or decrease in rCBF. The intensity of CLBP was assessed by NRS and by DN4. RESULTS: The results demonstrated an rCBF increase in clusters A (occipital and posterior cingulate cortex) and B (right frontal) and a decrease in cluster C (superior parietal lobe and middle cingulate cortex). NRS scores were inversely and moderately correlated with the intensity of rCBF increase in cluster B, but not to rCBF changes in clusters A and C. DN4 scores did not correlate with rCBF changes in all three clusters. CONCLUSIONS: This study will be important for future therapeutic studies that aim to validate the association of rCBF findings with the pharmacokinetic and pharmacodynamic profiles of therapeutic challenges in pain.

Translation, Cross-Cultural Adaptation, and Validation of the Portuguese Version of the Rotterdam Elderly Pain Observation Scale.

INTRODUCTION: This study reports on the translation, cultural adaptation, and validation of a Portuguese version of the Rotterdam Elderly Pain Observation Scale (REPOS), a Dutch scale to assess pain in patients who cannot communicate, with or without dementia. METHODS: This is a multicenter study in pain and neurological units involving Brazil (clinical phase) and the Netherlands (training phase). We performed a retrospective cross-sectional, 2-staged analysis, translating and culturally adapting the REPOS to a Portuguese version (REPOS-P) and evaluating its psychometric properties. Eight health professionals were trained to observe patients with low back pain. REPOS consists of 10 behavioral items scored as present or absent after a 2-min observation. The REPOS score of ≥3 in combination with the Numerical Rating Scale (NRS) of ≥4 indicated pain. The Content Validity Index (CVI) in all items and instructions showed CVI values at their maximum. According to the higher correlation coefficient found between NRS and REPOS-P, it may be suggested that there was an adequate convergent validity. RESULTS: The REPOS-P was administered to 80 patients with a mean age of 60 years (SD 11.5). Cronbach's alpha coefficient showed a moderate internal consistency of REPOS-P (α = 0.62), which is compatible with the original study of REPOS. All health professionals reached high levels of interrater agreement within a median of 10 weeks of training, assuring reproducibility. Cohen's kappa was 0.96 (SD 0.03), and the intraclass correlation coefficient was 0.98 (SD 0.02), showing high reliability of REPOS-P scores between the trainer (researcher) and the trainees (healthcare professionals). The Pearson correlation coefficient was 0.95 (95% confidence interval 0.94-0.97), showing a significant correlation between the total scores of REPOS-P and NRS. CONCLUSION: The REPOS-P was a valuable scale for assessing elderly patients with low back pain by different healthcare professionals. Short application time, ease of use, clear instructions, and the brief training required for application were essential characteristics of REPOS-P.