Diagnostic epidural opioid blockade and chronic pain: preliminary report

A technique is described which helps in the differentiation between pain of a mainly physical (organic) and emotional (psychogenic) basis. This is based upon the patients' subjective response to the epidural administration of fentanyl and placebo agents. Patients initially had both physical and psychological assessment in a multidisciplinary pain management unit and because of doubt of the underlying diagnosis, were subjected to this procedure. Eight patients are described in whom the following solutions were administered at 20 min intervals: 2 aliquots of normal saline (5 ml) via an epidural catheter; 1 microgram/kg fentanyl via the epidural catheter; intravenous naloxone 0.4 mg, then, depending upon results obtained, 15-20 ml 2% plain lignocaine via the epidural catheter. If a patient's visual analogue score decreased following epidural fentanyl and subsequently increased following naloxone, then a predominantly physical basis for the pain was likely. In contrast, little change in visual analogue score following fentanyl and naloxone suggested a diagnosis of a predominantly emotional basis for the pain. The diagnoses were substantiated by subsequent follow-up and treatment. It is suggested that this test has both prognostic and diagnostic value when used in the context of thorough physical and psychologic assessment of a patient with chronic pain.