The lumbar (low back) sympathetic plexus is a collection of nerves that carries sympathetic nervous supply to the lower extremities. The plexus lies in front of the psoas muscle at lumbar vertebral levels L2, L3, and L4.

The sympathetic nervous system is responsible for the body's response during the times of stress or danger.  In addition, sympathetic nervous impulses cause the constriction of peripheral blood vessels. Sometimes a sympathetic nerve may be unnecessarily stimulated as a result of injury or other trauma to the body.  In this situation, the involved sympathetic nerve will cause the blood vessels in the arm or leg to constrict and remain constricted, resulting in poor circulation to that limb.  The patient may then experience pain and possibly swelling, skin and nail changes, unusual color of the skin and temperature changes in the limb.  By blocking the sympathetic nerve impulses, the blood vessels widen, circulation is improved and pain relief may then result.

The most commonly treated condition is Complex Regional Pain Syndrome (CRPS) or Reflex Sympathetic Dystrophy (RSD).  These blocks are also used in situations in which increased circulation to the limb will be beneficial for healing as in diabetic neuropathy or slow healing wounds

A lumbar sympathetic nerve block is most commonly used in the management of Complex Regional Pain Syndrome (CRPS).  These blocks are also used in the management of pain arising secondary to ischemia and diabetic neuropathy.

The medication often used is a local anesthetic, which is temporary (effective for several hours). Although the local anesthetic provides short term pain relief, the nerve block may provide relief from chronic pain for days to weeks.