Impaired selective attention in chronic pain patients.

Several recent studies have suggested that cognitive complaints among chronic pain patients could result from an interference between ongoing pain and mental tasks, as they share common and limited attentional resources. This study was intended to further explore that presumed relationship between chronic pain and attentional disorders. For this purpose, a more sensitive version of the conventional colour-word Stroop task, with four subtasks of increasing difficulty, was used in a group of 33 consecutive patients with chronic non-malignant pain and a group of 20 healthy subjects as controls. This task assesses specifically selective attention. Since the Stroop task is sensitive to dysthymic states, levels of anxiety and depression were also assessed in chronic pain patients.As expected, the increase of response times was positively related to the difficulty of the subtasks. However, only the patients with chronic pain of high intensity presented a significant increase in the response times to each subtask as compared to controls. Response accuracy was not affected. Patients with high pain had higher scores on trait-anxiety than those with low-intensity pain. However, ANCOVA showed that trait-anxiety scores x pain groups interactions were not significant and thus that trait-anxiety was not useful for predicting task performance.These results point to a disturbance of selective attention as a function of pain intensity in chronic pain patients. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.