Sex differences in the stability of conditioned pain modulation (CPM) among patients with chronic pain.
OBJECTIVE
To examine the temporal stability of conditioned pain modulation (CPM), formerly termed diffuse noxious inhibitory controls, among a sample of patients with chronic pain. The study also examined the factors that might be responsible for the stability of CPM.


METHODS
In this test-retest study, patients underwent a series of standardized psychophysical pain-testing procedures designed to assess CPM on two separate occasions (i.e., baseline and follow up). Patients also completed self-report measures of catastrophizing (Pain Catastrophizing Scale [PCS] and negative affect [NA]).


RESULTS
Overall, results provided evidence for the stability of CPM among patients with chronic pain. Results, however, revealed considerable sex differences in the stability of CPM. For women, results revealed a significant test-retest correlation between baseline and follow-up CPM scores. For men, however, the test-retest correlation between baseline and follow-up CPM scores was not significant. Results of a Fisher's Z-test revealed that the stability of CPM was significantly greater for women than for men. Follow-up analyses revealed that the difference between men and women in the stability of CPM could not be accounted for by any demographic (e.g., age) and/or psychological factors (PCS and NA).


CONCLUSIONS
Our findings suggest that CPM paradigms possess sufficient reliability to be incorporated into bedside clinical evaluation of patients with chronic pain, but only among women. The lack of CPM reproducibility/stability observed among men places limits on the potential use of CPM paradigms in clinical settings for the assessment of men's endogenous pain-inhibitory function.
Department of Anesthesiology, Harvard Medical School, Brigham & Women's Hospital, Boston, Massachusetts, USA.
Marc O
MO
Martel
Ajay D
AD
Wasan
Robert R
RR
Edwards
D000328:Adult; D058443:Catastrophization / Q000523:psychology; D059350:Chronic Pain / Q000523:psychology*; D003213:Conditioning, Psychological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D017288:Pain Threshold / Q000523:psychology*; D012727:Sex Characteristics
Catastrophizing; Chronic Pain; Conditioned Pain Modulation; DNIC; Negative Affect