2 Clinical Trials for Various Conditions
40 CRPS patients will be recruited over a three-year period (target of 160 patients at all sites). Assessment of exclusion criteria will be undertaken during initial recruitment. Exclusion criteria are: \<18 years; a second chronic pain syndrome that would interfere with pain rating; psychiatric comorbidity; pain in both hands or feet; pregnancy or breastfeeding; sympathectomy in the affected limb; use of topical medication; known sensitivity to alpha 1- adrenoceptor agonists or other contraindications. Patients will maintain their regular oral medications throughout the study period. Assessment of sympathetically maintained pain (SMP) will require an intradermal dose of Phenylephrine to rekindle SMP and mechanical hyperalgesia. Clonidine will be used to control for affects of algometer fiction and may inhibit SMP by inhibiting the release of more norepinephrine from sympathetic nerve terminals. Skin biopsies will be obtained under sterile conditions from a site of mechanical or thermal hyperalgesia using a 3mm diameter skin biopsy punch under local anesthesia. Samples from a mirror image site on the contralateral body side will also be taken.
Interventional pain procedures have diagnostic, prognostic and therapeutic value. It is well-documented that the reference standard for identifying a pain generator is a low-volume block performed with local anesthetic, with or without steroid. Many factors may increase the false positive (FP) rate of diagnostic and prognostic nerve blocks; however, the use of sedation is the most controversial and remediable. Proponents of sedation argue that it has little effect on the rate of positive diagnostic blocks, and may even reduce the false-negative rate. The purpose of this study is to determine the effect of intravenous sedation on pain relief and the "false-positive rate" after diagnostic nerve blocks.