Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Brain Activity in Patients with Chronic Knee Pain Due to Osteoarthritis: Dissociating Evoked from Spontaneous Pain.

Parks2,  Elle L., Baliki2,  Marwan N., Geha3,  Paul Y., Schnitzer1,  Thomas J., Apkarian2,  Apkar V.

Northwestern University, Chicago, IL
Northwestern University
Yale University

Background:

Although chronic pain is a primary manifestation of osteoarthritis (OA), its properties and representation in the brain have not been fully explored. Prior work from our group indicated that brain activity for spontaneous pain and evoked pain in people suffering chronic pain activate brain areas distinct from that observed for acute pain in healthy subjects1,2 but this has not been studied in people with OA.

Objectives:

To define: 1) Psychophysical differences in knee joint pressure-induced pain between OA and healthy subjects, and between OA patients' reported better and worse knees; 2) brain activity differences for knee joint pressure-induced pain in these groups; 3) brain activity differences for evoked and spontaneous pain in OA; 4) the representation of clinical OA pain characteristics in the brain and their relationship with spontaneous and evoked pain-related activity;

Methods:

Fourteen OA patients (10 males; age 56.1 ± 2.09 years) and nine healthy controls (6 males; age 46.55 ± 2.6 years) were recruited for this study. Subjects rated pain using a finger-span device in response to pressure applied by means of a custom-made apparatus to the most sensitive part of each knee for patients, and at the center of the knee joint in healthy controls. During each scan run subjects were presented with up to nine stimuli distributed in time in a pseudo-random design of variable intensities and durations. The pressure signal and finger-spanning device were synchronized and time locked with the fMRI acquisition sequence.

Results:

Psychophysical properties and brain activation patterns of evoked pain were similar between OA patients and healthy controls, and between worse and better OA knees. In OA patients, stimulus-related brain activity could be distinguished from brain activity associated with ongoing pain. The former activated brain regions (bilateral insula, SII, ACc, SMA, inferior and posterior parietal cortices) commonly observed for acute painful stimuli in healthy subjects, while the spontaneous pain of OA engaged prefrontal-limbic regions closely corresponding to areas observed for spontaneous pain in other chronic pain conditions, such as chronic back pain and post-herpetic neuralgia. We also identified, for the first time, arthritis and chronic pain-related clinical characteristics in the brain, which mapped to distinctive but overlapping prefrontal-limbic regions similar to those involved in spontaneous OA pain.

Conclusion:

This study demonstrates the existence of two distinct pain states in knee OA patients. Knee pressure-evoked pain activates brain regions commonly observed for acute pain in healthy subjects for the same stimulus while ongoing spontaneous OA pain activates mainly medial prefrontal-limbic cortical areas, corresponding closely to brain areas activated for spontaneous pain in chronic back pain patients1,2.

1.Baliki, MN, Chialvo, DR, Geha, PY & Levy, RM, et al (2006) Chronic pain and the emotional brain: specific brain activity associated with spontaneous fluctuations of intensity of chronic back pain. J Neurosci26:12165-12173

2.Apkarian, AV, Baliki, MN & Geha, PY (2009) Towards a theory of chronic pain. Prog Neurobiol87:81-97

To cite this abstract, please use the following information:
Parks, Elle L., Baliki, Marwan N., Geha, Paul Y., Schnitzer, Thomas J., Apkarian, Apkar V.; Brain Activity in Patients with Chronic Knee Pain Due to Osteoarthritis: Dissociating Evoked from Spontaneous Pain. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :2097
DOI: 10.1002/art.29862

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