Can a pharmacological pain analysis be used in the assessment of chronic low back pain?

A battery of pharmacological tests was used to differentiate the pain in patients with chronic low back pain (CLBP) referred for pain diagnosis and assessment of whether surgery was indicated or not. Forty patients (mean age 39 years, range 22-51 years) suffering from CLBP (mean pain duration 5.9 years, range 1-12 years) participated. Three pharmacological approaches were used: (1) intravenous infusion of morphine, (2) intravenous infusion of lidocaine and (3) a diagnostic epidural opioid blockade. The patients were tested in a single-blind, placebo-controlled fashion. The pain was considered nociceptive if it decreased by 50% or more in response to both intravenous morphine and epidural fentanyl, but increased in response to intravenous naloxone. The pain was considered neuropathic if it decreased by 50% or more in response to both intravenous lidocaine and the epidural local anaesthetic. Patients who registered a pain decrease of 50% or more in response to saline were classified as placebo responders. Those who registered less than 50% pain decrease in all the tests were considered nonresponders. According to the results of the tests, 16 of the patients were classified as having nociceptive pain, 8 neuropathic pain, 2 were placebo responders, 10 non-responders and 4 were unclassified. The results support the idea that this battery of pharmacological tests can be used in the classification of CLBP patients into different pain categories. This approach may prove useful as a guide for further patient evaluation and as a basis for choice of a suitable treatment strategy.