An exaggerated inflammatory process is considered an important pathophysiological feature of
complex regional pain syndrome type 1 (CRPS-1). The hypothalamic-pituitary-adrenal (HPA) axis serves as a negative feedback mechanism for inflammatory processes. The present study examined the HPA axis function in patients with CRPS-1 by a determination of
cortisol concentrations in saliva. Three sets of saliva samples were sequentially collected from 24 patients with CRPS-1 during medication (on-Med), 72 h after stopping medication (off-Med) and 8h after the
oral administration of 1mg
dexamethasone. One set of saliva samples was collected from healthy controls. The
cortisol awakening response (CAR) and diurnal
cortisol decline (
DCD) were used as indices for HPA axis function.
Cortisol levels during the post-awakening period in patients were increased following withdrawal of medications. The CAR during the off-Med condition was disappeared after administration of
dexamethasone. Among the examined CRPS-related numerical variables, the frequency of spontaneous
pain attacks showed relationships with the indices of HPA axis function. After classifying the patients into two subgroups, we observed that the CAR and
DCD in patient who had a relatively high frequency of spontaneous
pain attacks (subgroup 5 ≤) were lower and less steep than those in patient who had a relatively low frequency of spontaneous
pain attacks (subgroup 0-4) for the on- and off-Med conditions. The CAR and
DCD in subgroup 5 ≤ during their off-Med condition were comparable to those in controls. These results suggest that the increase in frequency of spontaneous
pain attacks is associated with a reduced CAR and flattened
DCD in patients CRPS-1.