Often, impaired social and occupational function occur.Complex regional pain syndrome is a multifactorial disorder with clinical features of neurogenic inflammation (swelling in the central nervous system), nociceptive sensitisation (which causes extreme sensitivity or allodynia), vasomotor dysfunction (blood flow problems which cause swelling and discolouration) and maladaptive neuroplasticity (where the brain changes and adapts with constant pain signals); CRPS is the result of an "aberrant [inappropriate] response to tissue injury". The "underlying neuronal matrix" of CRPS is seen to involve cognitive and motor as well as nociceptive processing; pinprick stimulation of a CRPS affected limb was painful (mechanical hyperalgesia) and showed a "significantly increased activation" of not just the S1 cortex (contralateral), S2 (bilateral) areas, and insula (bilateral) but also the associative-somatosensory cortices (contralateral), frontal cortices, and parts of the anterior cingulate cortex. In contrast to previous thoughts reflected in the name RSD, it appears that there is reduced sympathetic nervous system outflow, at least in the affected region (although there may be sympatho-afferent coupling). Wind-up (the increased sensation of pain with time) and central nervous system (CNS) sensitization are key neurologic processes that appear to be involved in the induction and maintenance of CRPS.Compelling evidence shows that the N-methyl-D-aspartate (NMDA) receptor has significant involvement in the CNS sensitization process. It is also hypothesized that elevated CNS glutamate levels promote wind-up and CNS sensitization. In addition, there exists experimental evidence demonstrating the presence of NMDA receptors in peripheral nerves.
Both syndromes are also characterized by autonomic dysfunction, which presents with temperature changes (usually localized, but can be global), cyanosis, and/or edema.The patient may also experience localized swelling; extreme sensitivity to nonpainful stimuli such as wind, water, noise, and vibrations; extreme sensitivity to touch (by themselves, other people, and even light clothing or bedding/blankets); abnormally increased sweating (or absent sweating); changes in skin temperature (alternating between overly warm and cold); changes in skin colouring (from white and mottled to bright red or reddish-violet); changes in skin texture (waxy, shiny, thin, tight skin); softening and thinning of bones; joint tenderness or stiffness; changes in nails and hair (delayed or increased growth, brittle nails/hair that easily break); muscle spasms; muscle loss (atrophy); tremors; dystonia; allodynia; hyperalgesia; and decreased/restricted ability and painful movement of affected body part. Drop attacks (falls), almost fainting, and fainting spells are infrequently reported, as are visual problems.The symptoms of CRPS vary in severity and duration. Since CRPS is a systemic problem, potentially any organ can be affected. Symptoms may change over time, and they can vary from person to person. The more dynamic symptoms, especially vascular aspects (edema, temperature) and location of pain, can change numerous times a day.Previously, CRPS was considered to have three stages however more recent studies suggest people affected by CRPS do not progress through sequential stages and the staging system is no longer in wide use. Growing evidence instead points towards distinct sub-types of CRPS. Cause
Complex regional pain syndrome is uncommon, and its cause is not clearly understood.