The aim of the study was to evaluate the
analgesic effect of
lidocaine in a double-blind, controlled multi-center study on patients with atypical
odontalgia (AO)--a possible orofacial
neuropathic pain condition. Thirty-five consecutive AO patients (range 31-81 years) with a mean
pain duration of 7.2 years (range 1-30 years) were recruited from four different
orofacial pain clinics in Sweden. In a randomized cross-over design, 1.5 ml
local anesthesia (20mg/ml
lidocaine and 12.5 microg/ml
adrenaline) or 1.5 ml saline (9 mg/ml NaCl
solution) (placebo) was injected to block the painful area. The VAS
pain scores showed an overall effect of time (ANOVA: P<0.001) and treatment (ANOVA: P=0.018) with a significant interaction between the factors (ANOVA: P<0.001). Overall, VAS
pain relief was significantly greater at 15-120 min following the
lidocaine injections compared to the placebo
injections (Tukey: P<0.05). All patients demonstrated significant disturbances in somatosensory function on the painful side compared to the non-painful side as revealed by quantitative sensory tests, however, only one significant inverse correlation was found between percentage
pain relief and the magnitude of brush-evoked
allodynia (Spearman: P<0.01). In conclusion, AO patients experienced significant, but not complete,
pain relief from administration of
local anesthetics compared with placebo. The findings indicate that the spontaneous
pain in AO patients only to some extent is dependent on peripheral afferent inputs and that sensitization of higher order neurons may be involved in the pathophysiology of AO.