Feasibility of a Combination of Graded Pain Exposure and Graded Motor Imagery in People With Complex Regional Pain Syndrome Type 1

Mc-Gill Short Form Questionnaire : It is a self-administered questionnaire consisting of 15 descriptors, of which 11 are sensory categories and 4 are affective. Each pain descriptor contains four columns representing the categories 0: none, 1: mild, 2: moderate, and 3: severe. Participants must mark the level of descriptor that represents their pain. There is no cutoff score in the questionnaire; higher values indicate more pain. Additionally, the questionnaire includes a visual analog scale of pain, which is a validated and reliable metric for pain assessment

Pain Pressure Threshold: Measured using a handheld pressure algometer (PAIN TEST™ FPX 50). Algometry has shown excellent interexaminer reliability (ICC 0.91). Pressure pain thresholds will be assessed on the dorsal side at 2 local points and one away from the hand; the local points are located at the proximal interphalangeal joint of the third finger (point 1) and at the space between the first and second metacarpals (point 2). Additionally, dorsally at the middle third of the forearm (point 3), the mean values of three consecutive measurements will be taken and compared to the contralateral side.

For the lower extremity, two local points will be assessed on the foot and one at a distance; the local points are located at the metatarsophalangeal joint of the 1st (point 4) and 5th toes on the dorsal side of the foot (point 5), and the distant point is the Anterior Tibial Tuberosity of the same leg (point 6).

Cold Pressure Test; The experimental tonic pain will be induced by submerging the contralateral hand in cold water following the Cold Pressor Test (conditioning stimulus), and the assessment of pressure pain thresholds (test stimulus) will be performed before and during the application of the conditioning stimulus using a handheld algometer. The Cold Pressor Test (CPT) has shown to be a superior conditioning stimulus to pain by ischemia and is widely used to evaluate conditioned pain modulation. The CPT will involve keeping the contralateral hand submerged in water at 12±1ºC up to the wrist for a period of 2 minutes. The assessment of pressure pain thresholds will begin 45 seconds after immersion; the locations will be local to the affected extremity; for the upper extremity will be performed at point 2, and for the lower extremities at point 4.

Upper limb function will be analyzed using the Quick-Disabilities of the Arm, Shoulder, and Hand (QuickDASH) scale. This questionnaire consists of 11 items, with a minimum of 10 items needed to be validly completed. It assesses the difficulty in performing daily activities, work-related tasks, social or family relationships, as well as pain and difficulty sleeping on a Likert scale ranging from 1 (no difficulty/problem) to 5 (unable/extremely difficult pain). The average of the responses is calculated, subtracting 1 from the total, and then multiplied by 25 to obtain a percentage related to the degree of disability, where higher values indicate greater disability. The QuickDASH has shown excellent test-retest reliability assessed by Lin's concordance coefficient of 0.80 and internal consistency greater than 0.9.

Foot and Ankle Ability Measure: (FAAM) scale will be used. This 29-item questionnaire assesses the physical function of individuals with foot or ankle-related disabilities. It consists of two subscales: the first one with 21 items evaluates activities of daily living (ADLs), and the second one with 8 items assesses sports activities. Higher scores indicate better function. Each item is scored on a 5-point Likert scale ranging from 0 (unable to perform) to 4 (no difficulty), with the option to answer N/A (not applicable) in case the activity is limited by any other aspect not related to the foot or ankle. The FAAM scale demonstrates high internal consistency (Cronbach's α for ADLs 0.97 and for sports 0.93) and test-retest reliability for ADLs (ICC=0.90) and for sports (ICC=0.76)

EQ-5D-5L questionnaire: The EuroQoL 5 dimensions 5 levels questionnaire assesses quality of life through five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. The EQ-5D-5L has demonstrated efficacy, reliability, and discriminative ability in multiple pathologies and populations. Users evaluate their perception of each dimension at the moment of assessment and have five Likert-type options ranging from 1 ("no problems") to 5 ("extreme problems"). The questionnaire also includes a Visual Analog Scale (VAS) for perceived quality of life. The set of values is categorized into a 5-digit code. The VAS is marked with a cross, and it indicates the perceived health status on that particular day.

Pain Catastrophizing Scale (PCS). The PCS is a self-administered questionnaire that assesses the construct of "Pain Catastrophizing" in response to the modulation of painful stimuli. It consists of 13 items that assess three different dimensions: rumination (items 8, 9, 10, 11), magnification (items 6, 7, 13), and helplessness (items 1, 2, 3, 4, 5, 12). The PCS shows reliable test-retest parameters (0.79) and internal consistency (Cronbach's α of 0.84)

Self-efficacy in Chronic Pain Questionnaire: this questionnaire assesses three dimensions with 22 items: self-efficacy in symptom control (items 1-8), self-efficacy in physical functioning (items 9-17), and self-efficacy in pain management (items 18-22). Each question is scored from 0 ("not at all capable") to 10 ("completely capable"), with a range of values from 0 to 100. The questionnaire has a test-retest reliability of r=0.75 and internal consistency (Cronbach's α of 0.91).

Hand-grip strength measured with a dynamometer: isometric handgrip strength will be calculated on the affected side using a JAMAR hydraulic dynamometer, while seated with a straight back and feet touching the ground. The elbow is flexed at a 90° angle, in a neutral position of forearm pronation and supination, close to the body, with a neutral wrist position, and in the most comfortable device position for the user (42). The user will be instructed to squeeze the device as hard as possible upon verbal command. Three measurements will be taken with 5 seconds of rest between each. The test-retest reliability of the handgrip strength measurement with this dynamometer is very high (r=0.88-0.93)