CRPS is an orphan disease and is a chronic pain condition characterized by spontaneous and evoked regional pain, usually beginning in a distal extremity, which is disproportionate in magnitude and/or duration to the typical course of pain following a particular tissue injury or trauma. It is distinguished from other chronic pain conditions by the presence of signs and symptoms indicating prominent autonomic and inflammatory changes in the area of pain. Patients may present with a limb displaying extreme hyperalgesia and allodynia (i.e., normally non-painful stimuli such as touch or cold are experienced as painful); obvious changes in skin color, skin temperature, and sweating relative to the unaffected side; edema and altered patterns of hair, skin, or nail growth in the affected region; diminished strength; tremors; and dystonia (Harden et al., 1999). CRPS is often associated with significant impairments in activities of daily living and ability to function.
There are currently no FDA approved therapies for the treatment of CRPS. Oral opioids are often used to treat short-term pain, but generally have poor efficacy. Spinal cord stimulators are also sometimes used, but are highly invasive, expensive and only provide temporary relief. For severe pain, multiple sub-anesthetic infusions of ketamine may be used. There remains a very high unmet need for FDA-approved efficacious therapies to treat CRPS and its symptoms.