Modulation of thermal pain perception by stress and sweet taste in women with bulimia nervosa

OBJECTIVES: To investigate if the increased pain threshold in women with bulimia nervosa (BN) may be due to chronic stress-induced analgesia. METHODS: We measured thermal pain threshold latency, blood pressure and heart rate in 21 women with BN and 21 healthy women (HW) under six consecutive conditions: rest I, mental arithmetic task, rest II, eating sweet food, rest III, coldpressor test. RESULTS: Thermal pain threshold latency was longer in BN than in HW in all six conditions. It increased during mental arithmetic test and remained increased during the rest of the experiment in both groups. In the BN group, the increase of pain threshold during mental arithmetic was positively correlated with illness duration. The differential modulation of pain threshold by stress in BN and HW could not be explained by autonomic system reactivity. In HW, the pain threshold increased more during eating and blood pressure increased more during mental stress; in BN, the pain threshold was highest in the mental stress condition and blood pressure was most increased during eating. During the cold pressor test, women with BN showed smaller blood pressure increase and tolerated the cold for shorter time than HW. CONCLUSION: The observed marked modulation of pain threshold by experimental stress suggests that stress-induced analgesia is unlikely to account for baseline pain insensitivity in BN. Increased pain threshold in BN is a stable yet incompletely understood phenomenon, which may be related to the predisposition to or maintenance of the disorder.