Central sensitization phenomena after third molar surgery: a quantitative sensory testing study.

BACKGROUND: Surgical removal of third molars may carry a risk of developing persistent orofacial pain, and central sensitization appears to play an important role in the transition from acute to chronic pain. AIM: The aim of this study was to investigate sensitization (primarily central sensitization) after orofacial trauma using quantitative sensory testing (QST). METHODS: A total of 32 healthy men (16 patients and 16 age-matched control subjects) underwent a battery of quantitative tests adapted to the trigeminal area at baseline and 2, 7, and 30 days following surgical removal of a lower impacted third molar. RESULTS: Central sensitization for at least one week was indicated by significantly increased pain intensity evoked by intraoral repetitive pinprick and electrical stimulation (p<0.05) including facilitation of temporal summation mechanisms (p<0.05), extraoral repetitive electrical stimulation (p<0.001), significantly more frequent aftersensation in patients (p<0.001), extraoral hyperalgesia due to single pinprick stimulation (p<0.05) and larger pain areas due to intranasal stimulation (p<0.001). Peripheral sensitization was indicated by intraoral hyperalgesia due to single pinprick (p<0.05). CONCLUSION: We found clear signs of sensitization of the trigeminal nociceptive system for at least one week after the surgery. Our results indicate that even a minor orofacial surgical procedure may be sufficient to evoke signs of both central and peripheral sensitization, which may play a role in the transition from acute to chronic pain in susceptible individuals.

Analgesic efficacy and safety of intravenous paracetamol (acetaminophen) administered as a 2 g starting dose following third molar surgery.

BACKGROUND: The recommended dose for intravenous (IV) paracetamol injection in adults is 1g, however pharmacokinetic and pharmacodynamic findings suggest that a better analgesia could be obtained with a 2 g starting dose. METHODS: A single-centre, randomised, double-blind, placebo-controlled, 3-parallel group study was performed to demonstrate the analgesic efficacy and safety of IV paracetamol 2 g. Following third molar surgery, patients reporting moderate to severe pain received a single 15-min infusion of either IV paracetamol 2 g, IV paracetamol 1g or placebo. Efficacy and safety were evaluated over 8 h. Laboratory tests were performed before and 48 h after drug administration. RESULTS: Two hundred and ninety seven patients (132 = IV paracetamol 2g; 132 = IV paracetamol 1g; 33 = placebo) were randomised and completed the study. The summed pain relief over 6h (TOTPAR6) was significantly superior with IV paracetamol 2 g as compared to IV paracetamol 1g and placebo (p < 0.0001). Pain relief scores of IV paracetamol 2g were significantly superior to IV paracetamol 1g and to placebo from T30' to T8h (p < 0.0001). Median duration of analgesia was significantly longer following IV paracetamol 2 g compared to IV paracetamol 1g and placebo (p < 0.0001). Adverse events occurred with the same frequency in the 3 treatment groups. No clinically significant changes from baseline were observed for vital signs or laboratory tests. CONCLUSION: The analgesic efficacy of a 2 g starting dose of IV paracetamol was superior over the recommended dose of 1g in terms of magnitude and duration of analgesic effect for postoperative pain following third molar surgery, with no significant difference between groups regarding safety.

Intravenous lidocaine relieves spinal cord injury pain: a randomized controlled trial.

BACKGROUND: Neuropathic pain in spinal cord injury is a common challenging therapeutic condition. The current study examines the analgesic effect of the sodium channel blocker lidocaine on neuropathic pain in patients with spinal cord injury and the predictive role of concomitant evoked pain on pain relief with lidocaine. METHODS: Twenty-four spinal cord injury patients with neuropathic pain at or below the level of injury were randomized and completed a double-blind crossover trial of 5 mg/kg lidocaine and placebo infused over 30 min. Twelve patients reported evoked pain, and 12 patients had no evoked pain. Spontaneous and evoked pains were assessed using a visual analog scale and quantitative sensory testing. RESULTS: Lidocaine significantly reduced spontaneous pain in all patients (P < 0.01) and in each of the two groups with (P < 0.01) and without (P = 0.048) evoked pain, with no difference in number of responders (pain reduction > or = 33%) between the patients with (n = 6) and without (n = 5) evoked pain. Lidocaine significantly relieved both at-level and below-level neuropathic pain and decreased brush-evoked dysesthesia but not cold allodynia, pinprick hyperalgesia, or pain evoked by repetitive pinprick. CONCLUSIONS: Lidocaine reduced neuropathic pain at and below the level of injury irrespective of the presence or absence of evoked pain. Results are consistent with a central-acting effect of sodium channel blockers acting on neuronal hyperexcitability. Agents (such as anticonvulsants or antiarrhythmics) with sodium channel-blocking properties may be a treatment option for spinal cord injury pain.

Overview on tools and methods to assess neuropathic trigeminal pain.

This article provides a brief overview of the tools and methods that may be useful to assess neuropathic trigeminal pain. Pain is a complex multidimensional and biopsychosocial experience. While the assessment of neuropathic trigeminal pain is complex, there are several meaningful ways available for the systematic assessment of neuropathic pain and its effects and manifestations. The key to such an analysis is a standardized pain history and examination and a good knowledge of pain mechanisms. Patients can be asked to provide detailed information about their spontaneous pain (ie, stimulus-independent pain), eg, quality, intensity, localization, time course, and modifying factors. Stimulus-dependent pain components can be characterized with clinical examination procedures and quantitative psychophysical techniques such as application of mechanical, thermal, chemical, and electrical stimuli. The description of the stimulus-dependent pain is important to reveal the function of the somatosensory system and to map the extent of hyperalgesia, hyperesthesia and allodynia, because the normal relationship between stimulus intensity and perceived intensity is distorted in many neuropathic pain conditions. In addition to the psychophysical techniques, a number of laboratory tests for assessment of trigeminal pain have been developed and tested, although critical information on sensitivity, specificity, and predictive values is still scarce. There is also a need for common guidelines on classification, diagnostic procedures, and management. This will require concerted international, interdisciplinary action.