Introduction: Deafferentation pain constitutes one of the most difficult pathological pain states to manage and it is often refractory to medical treatment.Combined targeting of the periaqueductal grey (PAG) and the ventral posteriorlateral (VPL) nucleus of the sensory thalamus is the most commonly used target combination in chronic pain1. As the understanding of the pain matrix develops, other potential target sites such as the centromedian-parafascicular (Cm-Pf) nucleus are being investigated supported by strong preclinical data demonstrating the role of the parafascicular complex in nociception.We present our experience in 7 patients ( phantom limb pain, anaesthesia dolorosa, brachial plexus avulsion)

Methods: All patients underwent DBS surgery under GA using our MRI-directed guide tube method. Within the CmPf, the parafasciular component of the nucleus was targeted. Assessments were carried out using the Visual Analog Scale (VAS), Neuropathic pain scale (NPS), brief pain inventory (BPI), the SF-36 form and quantitative sensory testing (QST) for a median follow up of 3 years. PAG was stimulated at 10Hz whilst VPL and CmPf were stimulated at 130Hz.

Results: Pain scores remained diminished across all measures for the entire follow up period, though this was only statistically significant for the 6 monthly follow up with the BPI summary. When looking at QST data, no changes in heat pain threshold or painful punctate mechanical threshold were detected in the non affected areas. There was a significant reduction in QOL measures and also in the opiate medication dosages post operatively. Within the cohort, patients who had PAG and CmPf had a 39% greater improvement in their VAS score than those with PAG and VPL stimulation. In the former group, PAG alone provided a significant drop in pain levels, however in all patients this wore off after 2 days to 8 weeks post surgery. At this time CmPf stimulation provided additional pain relief. Characterstically PAG stimulation was reported as a warm, pleasurable sensation over the affected area; in contrast on Pf stimulation, patients reported change in the character of the pain and feeling “less troubled” by it with increased functionality in the affected limb. This ties in with the affective pain pathway that CmPf relays into.

Conclusions: Although our cohort is small with a non-homogenous patient group, CmPf stimulation combined with PAG appeared to be more effective than PAG with VPL or PAG alone.

Patient Care: This research is investigating novel target combinations for DBS to treat a refractory condition that continues to be challenging to treat.

Learning Objectives: Readers should be able to 1) learn about potential new target combinations for treatment of de-afferentation pain 2) pain assessment measures that could be used to assess such pain measures

References: 1. Levy R et al. Intracranial neurostimulation for pain control: a review. Pain Physician. 2010;13(2):157-65. 2. Shi T et al. L-364,718 Potentiates Electroacupuncture Analgesia Through Cck-A Receptor of Pain-Related Neurons in the Nucleus Parafascicularis. Neurochemical Research. 2011;36(1):129-38. 3. Patel NK et al. Magnetic resonance imaging-directed method for functional neurosurgery using implantable guide tubes.Neurosurgery. 2007 Nov;61(5 Suppl 2):358-65; discussion 365-6.