Patients with "
reflex sympathetic dystrophy" or "
causalgia" underwent sympathetic blocks. In protocol A (77 patients), we infused placebo (saline) for 30 minutes followed by
phentolamine (35 mg). In protocol B (23 patients), the saline phase was followed by double-blind infusion of
phentolamine or
phenylephrine (500 micrograms), a second phase of saline, and then the other active
drug. We assessed magnitudes of
pain and mechanical
hyperalgesias on a 0-to-10
pain scale and monitored sensory and sympathetic effects. With protocol A,
pain diminished significantly (> or = 50%) during placebo in 22 patients (28.9%) and during
phentolamine in seven (9.2%). With protocol B, four patients (17.3%) had relief of
pain during placebo, four (17.3%) during
phenylephrine, and two (8.7%) during
phentolamine. All "
phentolamine responders" had progressive
pain relief from placebo. Two patients expressed relief during
phenylephrine and worsening during
phentolamine. Most patients did not respond significantly to saline or drugs. Thus, pharmacologic manipulation of the
alpha-1 adrenergic receptor by either agonist or antagonist
drug does not influence
neuropathic pains. These results raise questions about the existence of "sympathetically maintained
pain," as diagnosed by sympathetic blocks improperly controlled for placebo.