S38 Abstracts (748) Assessment of pain quality in a clinical trial of gabapentin extended release for postherpetic neuralgia (750) Botulinum toxin ...

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(748) Assessment of pain quality in a clinical trial of gabapentin extended release for postherpetic neuralgia

(750) Botulinum toxin type A for refractory low back pain: Who is most likely to respond?

M Jensen, Y Chiang, M Cramer, B Berner, J Wu, G Irving; University of Washington School of Medicine, Seattle, WA Although many pain treatments have similar effects on global measures of pain intensity or unpleasantness, a growing body of evidence suggests that different treatments have differential effects on specific qualities or domains of pain. Knowledge about the effects of different treatments on specific pain qualities could help determine similarities and differences in the mechanisms of action of pain treatments, as well as help clinicians to target pain treatments to the most appropriate individuals or conditions. We performed secondary analyses on data from a randomized, double-blind, placebo-controlled trial of Gabapentin Extended Release (G-ER) in patients with postherpetic neuralgia (PHN) to identify the effects of this treatment on overall pain and specific pain qualities. Patients were titrated to their assigned treatment (G-ER 1800 mg/day dosed either once- or twice-daily or placebo) over 2 weeks and remained at that dose for an additional 2 weeks. Results of the primary analysis showed significant differences between G-ER twice-daily and placebo for reductions from baseline in average daily pain score (p⫽0.014), average daily sleep interference score (p⫽0.006), and an average of 10 items on the Neuropathic Pain Scale (NPS; p⫽0.019). There was also a trend towards significant differences between G-ER oncedaily versus placebo for changes in these measurements. Secondary analyses indicated that G-ER, especially when administered twice-daily, had the greatest effects on sharp, dull, sensitive, and itchy pain, with significant differences between G-ER twice-daily and placebo for changes from baseline in NPS scores for these parameters. These findings provide support for the potential importance of assessing specific pain qualities as outcomes in clinical trials. If replicated in other samples, the findings may also be used by clinicians to identify those patients for whom G-ER may be particularly effective; i.e., patients with PHN presenting with pain that they describe as sharp, dull, sensitive, or itchy.

K Edwards; Neurological Research Center, Bennington, VT Chronic low back pain (LBP) can be a debilitating syndrome with musculoskeletal and neuropathic pain features. Botulinum toxin type A (BoNT-A) is FDA approved for the treatment of cervical dystonia, blephoraspasm, hemifacial spasm and other conditions but is also used widely for treatment of migraine headaches, limb spasticity from stroke, multiple sclerosis and other causes, often with reduction of pain. Prior studies have shown that BoNT-A is efficacious for LBP. Animal studies suggest that BoNT-A may be efficacious for pain not only by the known neuromuscular blocking mechanism for relief of spasm but also by modulating substance-P, glutamate receptors, peripheral nociceptors and other neuropathic pain messenger systems. BoNT-A may have a unique benefit in patients with chronic LBP which often has both a musculoskeletal and neuropathic component. Cutaneous allodynia may accompany post-operative LBP, and BoNT-A has been shown to be effective with cutaneous allodynia such as in post-herpetic neuralgia. We have reviewed 80 patients who have received BoNT-A for LBP over the last 3 years with good results and have identified 10 patients who have been the most benefited in an attempt to predict which patients may be more likely to respond to BoNT-A treatments, especially after failing surgery, intervential blocks, physical therapy and medications. These 10 patients have all been post-laminectomy patients who have had cutaneous allodynia as a complication of their post-laminectomy syndrome. There may be a special responsiveness to BoNT-A treatment for patients with neuropathic pain accompanied with cutaneous allodynia in the post-laminectomy patient.

(749) Long term efficacy of botulinum toxin type A for post laminectomy syndrome

(751) A novel intra-articular treatment for refractory painful total knee arthroplasty (TKA)

K Edwards, B Rosenthal, J O’Connor; Neurological Research Center, Bennington, VT Low back pain (LBP) patients who have persistent LBP with radiculopathy following back surgery are among the most difficult to treat. Prior studies have shown that botulinum toxin type A (BoNT-A) is efficacious for LBP. We retrospectively reviewed charts of 26 consecutive patients who had prior lumbar surgery with persistent somatic and radicular pain, who had failed multiple other treatments. and who were treated with repeated BoTN-A injections every 3 months for over 3 years. Pain ratings included the Visual Analogue Scale (VAS), the Short Form McGill Pain Questionnaire (SF-MPQ) and Present Pain Intensity (PPI) before injection and at 4 to 8 weeks post-injection. Patients received 300 to 400 units of BTX in the paralumbar muscles. Most patients received BoNT-X injections via an 1 1⁄2 inch, 27 gauge needle Occasional injections were performed using EMG guided technique usually with a 26-gauge, 37 mm needle to ensure intramuscular injection when the post-operative scaling is such that it is difficult to determine the injection site location without EMG guidance. These patients had significant pain reduction and functional improvement sustained with BoNT-A. Pre-treatment VAS was 73.9 with a post-treatment VAS is 57.2 (p⫽0.001). SF-MPQ mean was 19.4; post-treatment SF-MPQ mean was 17.7 (p⫽NS). Pre-treatment PPI mean was (3.0); post-treatment PPI mean was 2.4 (p⫽NS.). Side effects were limited to transient injection site discomfort. No patient developed weakness. Most patients continued to have BoNT-A injections at 3 month intervals with continuing, and usually, increasing benefit. BoNT-A appears to be effective in a high percentage of patients with significant, long-term LBP who have failed surgery and multiple other modalities of treatment. No significant side effects occurred in any of our patients.

J Singh, M Mahowald, E Santos, R Schmidt, T Gioe; Minneapolis VA Medical Center, Minneapolis, MN Painful TKA without clear etiology can be a difficult management problem. We report data on off-label use of Intra-articular Boutlinum Toxin A (IA-BoNT/A) for refractory painful TKAs. Case-series of five patients with six refractory painful TKAs (failed all conservative options including oral analgesics/anti-inflammatory medications) with pain duration ⬎12months received 100-units of IA-BoNT/A followed by re-injection of 200units 8-12 weeks later for non-responders. Infection, prosthetic loosening and other surgically correctable causes of pain were ruled out. Data was collected prospectively: pain severity on 0-10 numeric rating scale (NRS), onset and duration of pain relief, patients’ global assessment of change (7-point scale ranging from very much improved{very much worse) and adverse effects. 5/6 painful TKAs had ␮30% and 3/6 had ␮50% reduction in Daytime pain (Table). 4/5 painful TKAs had ␮30% and 3/5 had ␮50% reduction in Night-time pain. 5/6 painful TKAs had “much improvement” on global assessment. Pain relief lasted 3-40 weeks. No increase in joint inflammation, periarticular muscle weakness, fever/fatigue, or other complications were noted.