Why do people with complex regional pain syndrome take longer to recognize their affected hand?

BACKGROUND: People with complex regional pain syndrome (CRPS) take longer to recognize the laterality of a pictured hand when it coincides with their affected hand. The author explored two aspects of this phenomenon: whether the duration of symptoms relates to the extent of the delay and whether guarding-type mechanisms are involved.
METHODS: Eighteen patients with CRPS type 1 of the wrist and 18 matched control subjects performed a hand laterality recognition task. McGill pain questionnaire, Neuropathic Pain Scale, and response time (RT) to recognize hand laterality were analyzed. Regressions related 1) mean RT for patients to the duration of symptoms and to pain intensity; and 2) mean RT for each picture to the predicted pain on executing that movement as judged by the patient, and to the awkwardness of the movement that would be required.
RESULTS: For patients, the duration of symptoms correlated with mean RT (Spearman rho = 0.44; p = 0.02). Predicted pain rating explained 45% of the variance in RT for each picture for each patient (p < 0.01).
CONCLUSIONS: The results suggest that in patients with complex regional pain syndrome type 1, delayed recognition of hand laterality is related to the duration of symptoms and to the pain that would be evoked by executing the movement. The former is consistent with chronic pain and disuse and may involve reorganization of the cortical correlate of body schema. The latter is consistent with a guarding-type response that probably occurs upstream of the motor cortex at a motor planning level.