Somatosensory Studies of Pain and Pain Control Measured With Oxygen-15 Water Positron Emission Tomography and Functional MRI in Normals and Patients With Neuropathic or Chronic Pain Conditions

Regional cerebral blood flow (rCBF) will be measured while normal subjects, patients with post-operative pain, and patients with neuropathic abnormalities of pain sensation are exposed to a battery of somatosensory stimuli that activate known pathways subserving touch, temperature and pain sensations. We have performed a series of studies on the genetics of pain, which assessed sensitivity (via subjective ratings) to a series of warm and painfully hot thermal pulses. Subjects ranged from insensitive (i.e. rating 49 degrees C as a 0.8 versus a 10 on a 10 point scale), yet mathematically we could define an inflection point at the transition from warm to hot in nearly everyone, thus they most subjects encode the nociceptive input and they all alter their ratings at the threshold for C-fiber afferent firing (45 degrees C). We need to understand how the brain responds using objective blood flow endpoints. Our previous studies disclosed distinct pain-intensity driven network of regions activated by hot thermal stimuli and we will use repetitive scans to determine the degree of activation of this network in the sensitive and insensitive subjects. We have also developed a new treatment for cancer and arthritic pain that involves deletion of the primary afferent C-fibers. We are in the midst of getting approval from the FDA for use of this in patients with cancer pain. Assuming we obtain approval, we may then have the potential to scan some of the appropriate patients before and after treatment to determine the impact of the treatment and to explore alterations in the pain network in subjects with and without C-fiber afferents using experimental stimuli. We also expect to eventually treat patients with peripheral neuropathies and other chronic pain conditions that cause spontaneous pain, hyperalgesia, and allodynia (pain sensation to a normally non-noxious stimulus) and they will be examined with and without applied experimental stimuli before and after treatment.