The investigators would like to examine the role of some relevant biopsychosocial factors in the development of persistent CRPS. According to the International Classification of Functioning, Disability and Health (ICF) [43], the outcomes will belong to one of the three following components:

• Body structures and functions (pain, CRPS severity score (CSS)),
• Activities (disability)
• Participation (return to work, quality of life). The primary aim is to assess predicting factors for chronification.

The secondary aims are:

• to evaluate if it is possible to classify acute complex regional pain syndrome (CRPS) patients into subgroups according to their risk of chronification.
• to document the course of the disease. The main evaluation criteria will be to determine the impact of the different clinical and non-clinical variables on the course of the CRPS and on the aforementioned outcomes then, which will use as endpoints.
• Primary endpoint: disability
• Secondary endpoints: participation-QoL, return to work, pain, CRPS severity score.

Patients suffering from early CRPS will be invited to attend 4 medical interviews over a 1-year period. A series of clinical data will be collected during this interview. After each consultation, the patient will be asked to complete a series of questionnaires at home (paper forms or online by REDCap). These questionnaires assess various psychosocial factors well known in the chronification of pain (fear of movement, anxious or depressive traits, "general" pain sensitization, social support, cognitive strategies to cope with pain) as well as the functional impact of the pathology.

All the study (first face-to-face assessment or follow-up sessions) will take place at Institute of Neurosciences (UCLouvain, site Woluwé) and perform by Pr. Berquin or Dr. Louis. As part of the study, the patients will never be assessed in another location or by another investigator.

After having encoded the patients' details in the REDCap application, the participants will receive an automatic e-mail at every time point. It will include a link to the online survey. At any given moment of the study, they can contact the co-investigator (Dr. Louis) by e-mail or phone for any questions or help in completing the questionnaires. If necessary, the co-investigator will provide assistance by telephone

To simplify the recruitment process, the informed consent will be sent by post or e-mail and signed during the first meeting.

Five endpoints will be tested using linear mixed-effects regression models for repeated measures:

Primary endpoint: disability Secondary endpoints: participation-QoL, return to work, pain, CRPS severity score.

A latent profiles analysis will be performed to classify patients into subgroups based on variables at baseline and the risk of chronicity of profile will be computed.

Inclusion Criteria:

1. Aged over 18,
2. Meeting the clinical Budapest criteria,
3. Apparition of symptoms from less than 6 months,
4. CRPS type I or II,
5. Capacity to understand and voluntarily sign an informed consent form in French.

Exclusion Criteria:

1. Insufficient French language skills to answer questionnaires,
2. Personal history of CRPS at the same limb,
3. Post-stroke CRPS type I ("shoulder-hand syndrome"),
4. Psychiatric disorders that would interfere with the participants' ability to complete study tasks,
5. The following hormonal situations: gravidity, lactation, gender-affirming treatment,
6. Any other reason to exclude the subject because it may interfere with the study, according to judgment by the investigator. The reason will be documented.