Brain PET Scans in Patients with Minimal Pain

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Brain PET Scans in Patients with Minimal Pain
Asokumar Buvanendran, MD, Amjad Ali, MD, Travis
R. Stoub, PhD, Jeffrey S. Kroin, Ph.D., Kenneth
J. Tuman, M.D.
Departments of Anesthesiology, Radiology, and
Neurology Rush University Medical Center Rush
Medical College Chicago, IL
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Introduction

• Positron emission tomography (PET) is an imaging
  technique that can quantify increases in nerve
  cell activity in selective regions of the brain.
  
• Earlier studies have examined the pattern of
  increased brain activity that follows
  experimentally-induced acute pain.1,2,3

1 Brain 1998121931. 2 J Neurophysiol 1999
821934. 3 Anesth Analg 2007 1051784.
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Is Seeing Believing?
Can Pain Be Measured?
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Increased Activity in the Brain with Pain

• 6 different areas are being studied
• Anterior Cingulate Cortex (ACC)
• Primary Somatosenory Cortex (S1)
• Secondary Somatosensory Cortex (S2)
• Insular Cortex (IC)
• Pre-frontal Cortex (PF)
• Thalamus

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Moderate Postoperative Pain and Brain Activation
After TKA

• Baseline MRI of the brain and PET scan
• Epidural Anesthesia and Analgesia for
  postoperative pain
• Stopped epidural Moderate pain ? PET
• Epidural infusing No Pain ? PET

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Postoperative Moderate Pain after Left TKA
Contralateral Somatosensory Cortex
Right side Precuneus
Thalamus
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Current Study

• However, baseline PET activity (pre-stimulation
  or pre-surgery) in the brain has not been
  examined in detail.
• Knowledge of baseline activity in patients with
  no pain or mild pain prior to surgical or
  anesthetic intervention is important for future
  research involving PET assessment of modulation
  of postoperative pain.
• In this study we examine PET brain activation at
  rest in six patients with minimal pain.

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Methods

• In a quiet room with low ambient light, fasted
  patients were injected intravenously with the PET
  radionuclide 18F-fluoro-2-deoxyglucose.
• After waiting at least 30 min, a brain PET scan
  was performed.
• Prior to each PET scan, pain scores were measured
  using the verbal rating scale, with 0no pain,
  10worst imaginable pain.

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Analysis

• For the patients, digital files of PET scans were
  co-localized with a standard stereotaxic MRI.
• To compare PET scans among different patients, a
  linear normalization was applied by dividing
  regional activity by whole brain activity for
  each scan.1
• A relevant increase in glucose metabolism was
  assumed if more than 50 adjacent voxels showed a
  Z score gt 2.2

1 Eur Neuropsychopharm 200212527-44. 2 JNNP
2003 74922
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Results
The mean baseline pain score in the six patients
was 1.17 (range 0-2).
PET activation in these subjects was primarily in
the occipital lobe, and putamen bilaterally
Putamen
Occipital lobe
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• There was no significant activation in
  pain-related regions

Somatosensory cortex (SI or SII)
SI
SII
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There was no significant activation in
pain-related regions
Anterior cingulate gyrus (ACC)
ACC
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There was no significant activation in
pain-related regions
Insula
Also, no activation in thalamus
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Discussion

• To fully comprehend acute, chronic, and
  postoperative pain PET studies, baseline brain
  activation must be characterized.
• In patients reporting minimal pain, we have
  established that there was no brain activation in
  pain-related regions.
• This suggests that changes in brain activation
  after intervention (e.g. joint replacement
  surgery) will not be obscured by the patients
  baseline brain activity as long as the baseline
  pain score is 2 or less.

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Some activity in superior temporal gyrus and
frontal cortex Not Pain Activated site
Frontal cortex
Sup Temporal Gyrus