Complex regional pain syndrome (or RSD) is a neuropathic pain syndrome that is frequently diagnosed by persistent pain after a soft tissue injury that is out of proportion to what would normally be expected. It almost exclusively begins as the result of an extremity injury. The pain varies in its severity from mild to debilitating. Various symptoms can be present and may include autonomic dysregulation (sweating, goose bumps, and initially a very warm extremity when compared to the other extremity). The extremity may also include a very deep red or rudy appearance, a bluish or cyanotic appearance or present as a mottled look.
The appearance can vary throughout the day. Neurogenic edema (swelling), movement disorder (tremor), allodynia (pain produced in response to a non painful stimulus) and later findings of a cool/cold extremity and atrophy are also common findings. The syndrome can spread to involve the other extremity and possibly the torso resulting in widespread/generalized pain. Despite a multitude of treatments, some patients remain refractory to all standard therapies. Severe disability can result.
Despite being described since biblical times, complex regional pain syndrome (CRPS) remains a difficult-to-treat condition. While there have been multiple therapies explored in the treatment of CRPS, NMDA antagonists such as ketamine continue to hold significant interest because of their potential ability to alter the central sensitization noted in chronic pain states. The most common use is for those that have a definite neuropathic component. Ketamine is a N-methyl-D-aspartate receptor antagonist. Ketamine can produce strong analgesia in neuropathic pain states presumably by inhibition of the N-methyl-D-aspartate receptor.
Other mechanisms are possibly involved including enhancement of descending inhibition and anti-inflammatory effects at central sites.Ketamine is an open-channel NMDA blocker that acts on those receptors whose Mg(2+) block has been lifted. It may be effective when standard treatments have failed. There is no standard dose, duration of treatment or frequency of infusions for ketamine.
