The Sympathetic Block, or injection, is a diagnostic & potentially therapeutic injection of numbing medicine administered in order to block or decrease a certain type of pain located in the head, neck, chest, arm, or leg- known as sympathetic maintained pain. This type of injection is administered to a group of nerves located in the neck or lower back that are part of the sympathetic nervous system. If an illness or an injury affects the sympathetic nervous system, it may not function optimally and cause pain. This type of injection can often help diagnose, and possibly treat sympathetically maintained pain. One of the conditions considered for this type of procedure is complex regional pain syndrome (CRPS) also called reflex sympathetic dystrophy (RSD).