Bulimia Nervosa and Pain Perception After Recovery

Bulimia nervosa (BN) can produce many varied symptoms. Some, like reduced sensitivity to pain, are still not well understood. According to an international team of researchers, reduced pain perception in BN isn’t related solely to disordered eating behavior and can persist even after recovery (Int J Eat Disord 34:331, 2003).

To assess pain thresholds among patients with BN, Drs. Daniel Stein and Walter H. Kaye and colleagues studied 11 recovered female BN patients and 15 healthy matched volunteers. All BN patients had been recovered for at least a year, but had no history of anorexia nervosa. The healthy volunteers were age-matched women whose weight remained between 90% and 115% of average body weight since menarche.

Measuring pain thresholds

Pain thresholds were determined with two tests. The first test used a thermal pain stimulator (TPS), a 75-watt light bulb, held 7 cm from the participant’s wrist. The pain threshold was defined as the total time, measured with a stopwatch from turning on the bulb until the person reported feeling pain. Pain tolerance was the total time measured from the time when pain was reported until the participant withdrew her wrist from the light.

A second method used to measure pain threshold was the submaximal effort tourniquet test, in which a tight bandage is placed around the upper arm and a handgrip dynamomenter is used to test time and grips. Subjects were asked to report the first feelings of pain, and the interval between that and the point when pain became intolerable was recorded.

Results: longer-lasting pain in those with BN

A significantly greater percentage of former BN patients had TPS pain thresholds that lasted longer than 8 minutes, compared with the controls. (Eight minutes had been established as the time limit for stopping the experiment.) As for the tourniquet test, the mean pain thresholds were 3.10 minutes for the BN patients and 1.15 minutes for the controls.

According to the authors, this is the first study that has shown that elevated pain threshold persists after recovery among BN patients. One explanation might be that reduced sensitivity to pain after recovery is actually a trait associated with the illness, although it is also possible that BN vcauses a reduction in pain thresholds. In one recent study, pain was thought to have a putative role in pain in maintaining BN. That is, binge-eating and purging may be a way patients can temporarily normalize an elevated pain threshold (Faris et al, 1998).

Other recent studies have pointed to the possibility that altered central serotoninergic activity may continue after recovery from BN (Kaye, Greeno, et al, 1998). Decreased pain sensitivity after recovery may also be linked to alterations in serotonin activity—for example, drugs that act on serotonin systems have been shown to affect pain sensitivity (Schreiber and Stein, 1996).

This was small study. Furthermore, the very nature of pain perception can change according to the methods used to test it. However, the authors note that their findings may merit further investigation.