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
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.
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.