Comprehensive Pain Programme to Determine Mechanism of Transition of Acute to Chronic Postsurgical Pain

Comprehensive Pain Programme to Determine Mechanism of Transition of Acute to Chronic Postsurgical Pain- Functional Brain Imaging, Quantitative Sensory Testing, Psychological and Genetic Screening: Prospective Cohort Study

To determine whether central sensitization is a mechanism of CPSP (chronic postsurgical pain) in women who will develop CPSP compared to women with no CPSP after hysterectomy. This mechanism is illustrated by a higher pain score in experimental pain models such as tonic heat stimulation, increased evoked mechanical temporal summation and increased wound hyperalgesia.

Chronic pain affects 9% of Singapore population resulting in major socioeconomic burden. Chronic postsurgical pain (CPSP) that persists for over 3 months could be related to nerve injury making this a strategic model to study the transition of acute to chronic pain. CPSP occurs in up to 50% after surgery and up to 32% after hysterectomy. Over 600000 hysterectomies were performed in the US in 2003 making CPSP a significant problem.

Investigators will perform this prospective cohort study to determine whether increased central sensitization and negative psychological experience are involved in the transition of acute to chronic pain after hysterectomy. Investigators will recruit 444 women undergoing hysterectomy and employ validated physical pain testing including tonic heat stimulation, mechanical temporal summation and wound hyperalgesia which had been shown to be related to central sensitization. Pain catastrophizing (negative thoughts of pain) and state trait anxiety scoring will be assessed for the impact of negative cognitive-affective experience on CPSP. A phone survey will be performed at 4 months to determine the primary outcome of CPSP. Arterial spin labeling will be used to delineate cerebral blood flow using arterial spin labeling, functional connectivity and structural connectivity to evaluate insula-anterior cingulate cortex differences in 30 women with CPSP compared to 30 women without CPSP.

In addition to evaluating whether central sensitization, negative psychological experience and activation of brain regions are different in women with CPSP after hysterectomy, the results of this study will elucidate potential mechanisms of CPSP development that will guide in future studies on potential novel therapeutic targets.

Inclusion Criteria:

• Anthropometric profile within the following range: age 21-70 yr, American Society of Anesthesiology status I and II women
• Benign condition such as fibroids or adenomyosis
• Abdominal or laparoscopic hysterectomy

Exclusion Criteria:

• Vaginal hysterectomy
• being pelvic pain
• Failure to adequately determine tonic heat stimulation and mechanical temporal summation
• History of drug dependence or recreational drug use
• Allergy to any study drugs