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Phentolamine sympathetic block in painful polyneuropathies

II. Further questioning of the concept of ‘sympathetically maintained pain’

Departments of Neurology and Neurosurgery, Good Samaritan Hospital and Oregon Health Sciences University, Portland. OR.

To test for the presence of "sympathetically maintained pain" (SMP), we administered placebo-controlled phentolamine sympathetic blocks to 14 patients with painful polyneuropathies. Six received IV infusion of saline for 30 minutes, followed by phentolamine (35 mg). In eight patients, the saline phase was followed by double-blind infusion of phentolamine or phenylephrine (500 µg), a second saline phase, and then the other active drug. We measured magnitudes of spontaneous pain and mechanical hyperalgesias on a 0-to-10 pain scale every 5 minutes and monitored sensory and sympathetic effects clinically and through quantitative thermotest and thermography. Five patients reported significant diminution of pain (> 50%), all in response to placebo. Neither phentolamine nor phenylephrine provided relief, although all patients had signs of physiologic abnormalities reputed to be determinants or predictors of SMP. These results complement previous studies demonstrating the nonexistence of SMP among "reflex sympathetic dystrophy" patients and further question the concept of SMP.

Address correspondence and reprint requests to Dr. José L. Ochoa, Neuromuscular Unit, Department of Neurology, Good Samaritan Hospital and Medical Center, 1040 N.W. 22nd Avenue, Suite 460, Portland, OR 97210.

Supported by NIH grants ROI NS, 24740, 24766, and 28747.

Received November 30, 1993. Accepted for publication in final form December 20, 1993.

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