Radiofrequency ablation near the bone-muscle interface alters soft tissue lesion dimensions.

BACKGROUND AND OBJECTIVES: Radiofrequency (RF) lesions are safe and effective in the treatment of spine pain; however, models developed to study factors affecting lesion dimensions have been performed in homogeneous media that may not accurately simulate human anatomy and electrophysiology. We present a novel ex vivo porcine model for performing RF lesion studies and report the influence of bone on projection of RF ablation lesions into soft tissue. METHODS: Radiofrequency lesions were performed in porcine rib specimens using monopolar 18-gauge, 10-mm straight active tip cannula, with a lesion temperature of 80°C for 150 seconds. Ten lesions were performed in pure porcine muscle tissue and abutting porcine rib bone with surrounding muscle. Lesions were exposed with dissection and measured with digital calipers. RESULTS: Maximal effective lesion radius approximately doubled against the bone compared with the pure muscle group (mean, 5.65 mm [95% CI, 5.43-5.87 mm] vs 2.68 mm [95% CI, 2.55-2.81 mm], P < .0001), although this was seen only in a vertical direction and not horizontally. In addition, the prelesion and postlesion impedance of the bone-muscle interface was consistently higher than the muscle-only interface (mean, 165.6 Ohm [95% CI, 146.6-184.6 Ohm] vs 137.8 Ohm [95% CI, 135.5-140.1 Ohm], P = 0.004; 144.3 Ohm [95% CI, 134.3-154.3 Ohm] vs 124.3 Ohm [95% CI, 119.3-129.3 Ohm], P = 0.001). Other dimensions and estimated volume were not significantly different. CONCLUSIONS: Bone adjacent to RF lesions alters the surrounding electrophysiological environment causing RF lesions to project further perpendicularly from the needle axis, vertically to bone, than previously expected. This phenomenon should be considered in the future modeling and clinical practice of RF.

Effect of delayed intrathecal administration of capsaicin on neuropathic pain induced by chronic constriction injury of the sciatic nerve in rats.

PURPOSE: The current study was designed to examine the antinociceptive effect of intrathecally administered capsaicin, a transient receptor potential vanilloid 1 receptor agonist, in a rat model of neuropathic pain induced by unilateral sciatic nerve chronic constriction injury. METHODS: Male adult Sprague Dawley rats were randomly assigned to six groups, and all rats underwent unilateral sciatic nerve chronic constriction injury. Two weeks after injury, five groups received intrathecal administration of either capsaicin in three different dosing regimens or equal volumes of vehicle. The other group received intrathecal capsaicin on the third day after nerve injury. The antinociceptive effect of capsaicin was assessed by measuring the capsaicin-induced change in thermal and mechanical response thresholds. RESULTS: Capsaicin (150-300 µg/100-200 µL), when administered by fast infusion or chronic infusions at 8 µL/hour or 1 µL/hour, attenuated thermal hyperalgesia as indicated by significantly prolonging paw withdrawal latency to noxious thermal stimulation. The antinociceptive effect of capsaicin was more profound in the injured limb compared to that in the uninjured limb. When capsaicin was administered on the third day after nerve injury, it failed to attenuate thermal hyperalgesia. No significant effect on the mechanical response threshold was observed with intrathecally administered capsaicin. CONCLUSION: Our data suggest that intrathecal capsaicin could significantly attenuate thermal hyperalgesia, depending on the time when the drug is given after nerve injury, and that the antinociceptive efficacy of intrathecal capsaicin positively correlates with the previously reported dynamic profile of spinal transient receptor potential vanilloid 1 activity after nerve injury.

Impulsivity but not sensation seeking is associated with opioid analgesic misuse risk in patients with chronic pain.

Impulsivity and sensation seeking have been associated with substance use disorders, including opioid use disorders. This pilot study sought to examine whether impulsivity and sensation seeking, as measured by the Barratt Impulsiveness Scale (BIS) and Sensation Seeking Scale (SSS), were associated with opioid analgesic misuse risk in chronic, low-back pain patients prescribed opioid analgesics. Participants were 42 chronic, low-back pain patients enrolled in a larger study examining problematic opioid analgesic use. Impulsivity was assessed using the BIS, sensation seeking was measured using the SSS, and opioid analgesic misuse risk was assessed using the Current Opioid Misuse Measure (COMM). Significant bivariate associations were found between the COMM and the following predictor variables: age and the three BIS subscales: Attentional Impulsiveness, Non-planning Impulsiveness, and Motor Impulsiveness. Using a multivariate linear regression, after controlling for age, the BIS subscales accounted for 29.0% of the variance in the COMM. Attentional Impulsiveness was the only significant BIS subscale. These results suggest a potential relationship between impulsivity, but not sensation seeking, and risk for opioid analgesic misuse. Impulsivity is not a prominent trait observed in chronic pain patients; however, it may be an important risk factor for opioid analgesic misuse for a subset of individuals with chronic pain. As such, these findings suggest that additional exploration of this potential risk factor is warranted.

Descriptors of pain sensation: a dual hierarchical model of latent structure.

UNLABELLED: Recently, the lexicon of pain was refined into a parsimonious set of words making up the Pain Descriptor System (PDS). The present study investigated the latent structure of the sensory category of the PDS with its 24 descriptors distributed equally across 8 subcategories. A sample of 629 chronic pain patients rated the degree to which each of these words described their pain. It was found that coldness-related words were rarely used and shared high covariance with other descriptors, thus warranting their removal as a subcategory. Confirmatory factor analysis of a previously theorized single higher-order model of 7 latent factors (each with 3 observed variables) resulted in poor fit, x(2)(181) = 377.72, P < .05; comparative fit index (CFI) = .915; root mean square error of approximation (RMSEA) = .04. This model was replaced with a dual higher-order model retaining the same 7 latent factors plus 2 higher-order factors corresponding to deep pain versus superficial pain. This model provided a good representation of the data, x(2)(181) = 301.07, P < .05; CFI = .948; RMSEA = .032. Therefore, descriptors of pain sensation differentiate sensory quality while also reflecting a fundamental dichotomy supported by neurophysiological research. Thus, the lexicon can illuminate pathophysiology, thereby clarifying pain diagnoses. PERSPECTIVE: Confirmatory factor analysis was performed on pain sensation descriptors used by 629 patients. This supported a hierarchical model with 7 lower-order factors plus 2 higher-order factors corresponding to deep pain versus superficial pain. By reflecting neurophysiology, this lexicon of pain can offer diagnostic clues.

Intravenous regional ketorolac and lidocaine in the treatment of complex regional pain syndrome of the lower extremity: a randomized, double-blinded, crossover study.

BACKGROUND AND OBJECTIVES: Intravenous regional blocks (IVRBs) with ketorolac and lidocaine have been reported to be useful in the treatment of complex regional pain syndrome (CRPS). This is the first controlled prospective study of IVRB with lidocaine and ketorolac for treatment of pain and edema in CRPS of the lower extremity in adults. METHODS: A prospective, randomized, double-blinded, crossover design was used. The primary outcome was overall pain numeric rating scale (NRS) at 1 week postinjection; secondary outcomes included pain with motion, allodynia, joint pain score, edema, range of ankle motion, skin temperature, and short-term pain relief. Ten of 12 adult patients diagnosed with unilateral lower extremity CRPS (type I) completed the study. Four IVRBs were performed 1 week apart in a random sequence with 50 mL lidocaine 0.5% and 0, 30, 60, and 120 mg ketorolac. RESULTS: Only 1 outcome achieved significant improvement; there was 1 day of significant pain reduction in the ketorolac groups (median NRS 6 to 4, P=0.002). Overall pain NRS (10-point scale, mean±SE) at 1 week was 6.2±0.53, 6.5±0.89, 6.0±0.88, 5.9±0.82, and 5.8±0.9 at baseline, 0, 30, 60, and 120 mg, respectively (P=0.8). Pain with movement was 7.15±0.69, 5.7±1.07, 6.1±0.86, 5.0±0.97, and 5.6±0.86, (P=0.059). Edema was not significantly reduced (2% reduction, P=0.6). CONCLUSIONS: IVRB with ketorolac and lidocaine produced only short-term pain reduction in patients with CRPS involving the lower extremity after 4 serial injections in our study group. Prospective study is warranted, particularly in the pediatric population.

P-A-I-N: a four-cluster MMPI typology for chronic pain.

A 4-cluster empirically derived MMPI typology for chronic pain sufferers has been demonstrated by combining the results of 10 investigative teams. These MMPI 'types' have been labeled P-A-I-N and appear to have important clinical and demographic correlates. Type P is the most 'psychopathological' looking as nearly all scales are usually elevated. Type P patients are extreme in their claims of physical illness, psychological distress and social maladaptation. Demographic correlates include poor education, high rates of unemployment, and limited household income. Type A is defined by a 'conversion V' on the 'neurotic' triad scales. It has no unique correlates. Type I has elevations on all of the neurotic triad scales and on no others. Type I patients appear to be the most physically infirm with multiple surgeries and hospitalizations. They may not improve physical status with treatment, but appear to benefit psychologically. Type N profiles are 'normal' in that no scale, except perhaps scale K, is often elevated. Type N patients are moderate in their claims of ill health, often are better educated and employed, and appear to respond well to treatment. Classification rules have been proposed to allow patient-typing without a computer. Use of these rules should allow programmatic research into treatment/type interactions even in the ordinary clinical setting. The typology appears well enough established to allow for prospective studies to test theoretical hypotheses drawn from the literature base.