Complex regional pain syndrome (CRPS) is a chronic pain condition characterized by continuing regional pain that is disproportionate in time to the usual course of any trauma. The pain is described as diffuse and/or regional, not in any specific dermatome or nerve territory but generally has a propensity for distal aspects of extremities. CRPS has two forms:
CRPS-I develops following injury with little or no obvious damage to nerves in the particular extremity (formerly called “reflex sympathetic dystrophy”).
CRPS-II presents following injury to a nerve (formerly called “causalgia”).
Both CRPS-I and CRPS-II have similar clinical presentations and treatments.
The exact pathophysiology of CRPS is not yet completely understood. The current understanding is that CRPS may be a manifestation of multiple pathophysiologies arising after a tissue or nerve injury to the area. What is clear that CRPS develops from dysfunction in the peripheral nervous systems (PNS) and central nervous systems (CNS), which can occur postinjury. This dysfunction manifests as a “wind-up” or overactivity of the nervous system which contributes to an exponential increase in the firing rate and prolonged discharge in response to stimuli. In addition, there is evidence of the N-methyl-d-aspartate (NMDA) receptor and its involvement in CNS and PNS sensitization in the CRPS response. There is likely dysfunction of the sympathetic nervous system (SNS) in the region affected; simultaneously there may be an immunogenetic modulatory component that promotes the development and maintenance of a hyperbolic neurogenic inflammatory state. Ultimately, no singular unifying pathophysiologic mechanism in the development of CRPS has been identified. New findings are continuously emerging.
CRPS usually develops after an inciting trauma or injury to an area of the body with CRPS II being notable for injury to the nerve. The most common affected areas are the limbs, with the fingers, hands, wrists, and ankles being particularly common. CRPS is characterized by excessive pain in the affected area. The pain may be described as out of proportion to inciting events, with qualities of burning, sharp, or stabbing sensation. The pain varies in its timing and duration. That is, it may be constant or intermittent and it may be chronic (>2 months) or acute (<2 months). The pain may radiate to other areas due to the vasomotor instability associated with the syndrome. Other symptoms include changes in skin color, temperature, and the presence of edema; the skin may become thin and shiny in appearance. Associated symptoms that may be present include allodynia and/or hyperalgesia, difficulty with muscle coordination, joint stiffness, dystonia, tremors or jerking of the affected limb, changes in sweating pattern and growth pattern of hair or nails.
The criteria for diagnosing CRPS are currently based on a detailed history and physical examination, which are necessary to differentiate CRPS from other neuropathic pain syndromes. While some consider CRPS a diagnosis of exclusion since its clinical presentation is similar to many neuropathies and pain syndromes, newer diagnostic criteria have been established to increase the sensitivity and specificity of the diagnosis. The differential of CRPS includes posttraumatic neuralgia, diabetic neuropathy, rheumatologic and inflammatory conditions, infectious diseases, arterial or venous occlusive diseases, and factitious disorder (via secondarily affecting changes in blood vasculature). Table 120-1 lists diagnostic criteria for CRPS I and II.