Preceding Pain and Development of Additional Pain in Patients With Complex Regional Pain Syndrome

This cross-sectional study will use a questionnaire-based method to gather information on pre-existing pain, before CRPS development, at the same site where CRPS then develops, and on additional pain (pre-existing or later developing) from a large cohort of patients with CRPS. This will allow a large amount of data to be collected in a time-efficient manner and enable comparison between different groups, for example, those who developed widespread pain before or after their diagnosis of CRPS. The investigators know from existing research that widespread pain is a relatively common phenomenon in patients with CRPS; on this basis they expect its frequency in the cohort to be such that they may be able to detect statistically significant patterns in its development, for example a different frequency in certain age groups. Thus the questionnaire will feature questions about the patient's CRPS diagnosis and any additional pain they have experienced, including its time course of development and nature. It will also include questions about other symptoms that are more commonly observed in chronic widespread pain than in CRPS, such as cognitive symptoms and sleep disturbance, and which form part of the ACR 2016 criteria for fibromyalgia syndrome diagnosis. Independently, given the unexpected finding of CRPS-preceding pains in the later CRPS-affected limb in a previous Walton Centre study, the investigators will also more systematically evaluate this phenomenon.