Mechanism and Treatment of Sympathetically Maintained Pain

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 lgometer iction 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.