Spatial distribution of pain in complex regional pain syndrome.

Pain often spreads away from the injured site in complex regional pain syndrome (CRPS), but what drives this process is unclear. To explore this, pain drawings were investigated in 136 patients in relation to the type and location of injury, pain intensity and quality, CRPS duration, subtypes, and hyperalgesia to thermal and mechanical stimuli. Areas of pain were quantified using the ImageJ polygon selection tool. The pain area in the affected limb increased in line with pain intensity and with indices of hyperalgesia in the affected limb and ipsilateral forehead (P's < 0.01). The pain area was greater in patients with proximal than distal limb injury, CRPS I than II, longstanding than acute CRPS, the warm than symmetrical or cold subtypes, and in patients who experienced burning pain and/or pins-and-needles (P's < 0.05). Together, these predictors accounted for 30.4% of variance in pain area in the affected limb (P < 0.001). Thirty-five patients were reassessed after 5 to 124 months. After an invasive treatment such as an electrical stimulator implant or sympathetic blockade (N = 20), the pain area decreased in the affected limb of 11 patients but increased in 9 others. The pain area increased during follow-up in most other patients, and pain developed spontaneously in a previously unaffected limb in a minority of cases-specifically, in those with a greater area of pain and stronger hyperalgesia in the affected limb at baseline. Together, the findings suggest that peripheral and/or central nociceptor sensitization is associated with pain expansion in CRPS.