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Relationship between thresholds to thermally and to mechanically induced pain in patients with eating disorders and healthy subjects
Pain, 67 (1996) 511-512 © 1996 International Association for the Study of Pain. 0304-3959/96/ $15.00
511
PAIN 3143
Clinical note Relationship between thresholds to thermally and to mechanically induced pain in patients with eating disorders and healthy subjects 1 Martina de Zwaana,*, Dagmar Bienera , Christa Schneiderb and Georg Stacherb aDivision of General Psychiatry, Department of Psychiatry and bpsychophysiology Unit, Department of Surgery, University of Vienna, Vienna (Austria)
(Received 22 August 1995, revised version received 16 March 1995, accepted 21 March 1996)
Summary
This paper presents the results of a correlation analysis comparing thresholds to thermally and to mechanically induced pain in 40 patients with eating disorders and 32 healthy control subjects. The correlation coefficients for the response to the two modalities of pain were 0.498 for the whole sample, 0.430 for the healthy subjects, and 0.402 for the patients with eating disorders. Although these results indicate a significant overlap in the individuals' responses to the two modalities of induced pain, the criterion suggested by Janal et al. (Pain, 58 (1994) 403-411) of a 'minimum correlation of 0.5 (that) would justify allowing one test to be considered equivalent to another' is not met.
Key words: Threshold to mechanically induced pain; Threshold to thermally induced pain; Anorexia nervosa; Bulimia nervosa
Introduction The relationship between the responses of humans to painful stimuli of different nature has been investigated in a small number of studies only. In 45 men, thresholds to pain induced by radiant heat, pressure, and electrical stimulation were found to be highly related (Clark and Bindra 1956). Similarly, thresholds to pain induced by the immersion of an arm into ice water, pressure, and electrical stimuli correlated significantly in 40 healthy subjects (Harris and Rollmann 1983). By contrast, in 24 healthy men exposed to heat, cold, pinch, and pinprick stimulation, only the thresholds to pain induced by heat and pinching were interrelated significantly (Lynn and Perl 1977). Janal et al. (1994) found near-zero correlations between measures of the sensitivity to noxious heat, cold, ischemic, and electrical laboratory pain in healthy volunteers as well as in patients with coronary artery disease. The present study was aimed at investigating the relationship between the thresholds to thermally and to mechanically induced pain in healthy
*
Correspondmg author: Martina de Zwaan, MD., Division of General Psychiatry, Department of Psychiatry, UnivefSlty of Vienna, Wiihnnger Gtirtel 18-20, A-1090 Vienna, Austria. I Part of the data gathered is contained in a paper accepted for publication in the Journal of Psychosomatic Research.
PI/ S0304-3959(96)03143-0
subjects as well as in patients with anorexia nervosa and bulimia nervosa. In patients with both eating disorders, thresholds to thermally (Lautenbacher et al. 1990, 1991) and to mechanically (Faris et al. 1992) induced pain have been found to be elevated.
Methods Thresholds to pain induced by thermal and mechanical stimulation were determined in 40 female patients hospitalized for the treatment of eating disorders, i.e. in 22 patients with anorexia nervosa and in 18 with bulimia nervosa, as well as in 32 healthy subjects of comparable age. Thresholds to mechanically induced pain were assessed using an Ugo Basile Analgesymeter (Ugo Basile, Biological Research Apparatus, Comerio, VA, Italy). Pressure stimuli were applied sequentially to the tips of digits II-V of the subjects' non-dominant hand using a motorized drive. The pressure exerted increased from 0 to a maximum of 1260 gat a rate of 80 gls. Subjects were instructed to press a button when they first perceived the pressure as painful. Thresholds to thermally induced pain were measured in response to radiant heat stimuli of constant intensity. Sequentially, eight different sites on the volar surface of the subjects' non-dominant forearms were exposed to the stimulus. The subjects were instructed to withdraw their forearm from the stimulator as soon as they perceived the heat stimulus as painful and thereby to indicate their pain threshold (Stacher et aI., 1986). In the analysis, the eight threshold values recorded in each individual were averaged. In the 32 healthy subjects, the test-retest reliability of the techniques to assess the thresholds to mechanically and thermally induced pain was determined by performing another series of measure-
512 TABLE I CHARACTERISTICS OF, AND DATA GATHERED IN, THE PATIENTS WITH EATING DISORDERS AND THE HEALTHY SUBJECTS (MEANS ± SD)
Age (years) Body mass index (kglm 2) Threshold to mechanically induced pain (g) Threshold to thermally induced pain (ms)
Patients (n = 40)
Healthy subjects (n 32)
22.9 ± 4.5 175±3.7 668.6 ± 237.6
24.0 ± 3.6 22.3 ± 3.6* 496.4 ± 169.4*
3108±691
2597 ± 465*
=
*t-test for sample means, P < 0.001.
ments 7 days after the first testing. The study was approved by the Ethical Committee of the Faculty of Medicine, University of Vienna.
Results
The mean thresholds to mechanically induced pain were significantly related to the mean thresholds to thermally induced pain (Pearson product-moment correlation: overall, r(70) = 0.498, P < 0.001; healthy subjects, r(30) = 0.430, P < 0.014; and patients, r(38) =0.402, P < 0.01). Thresholds to mechanically as well as to thermally induced pain differed significantly between the patients with eating disorders and the healthy subjects: the patients had significantly higher thresholds for both mechanically (t-test for sample means, t(70) =3.45, P < 0.001) and thermally induced pain (t(70) =3.58, P < 0.001; Table I). The testretest reliability for the threshold to mechanically induced pain as well as for the threshold to thermally induced pain was high (r(30) = 0.709, P < 0.001, and r(30) = 0.663, P < 0.001, respectively).
Discussion
The results show that, in the patients with eating disorders as well as in the healthy subjects, the thresholds to mechanically induced pain correlated significantly with the thresholds to thermally induced pain. The high test-retest reliabilities found in the healthy subjects for the thresholds to the two types of noxious stimuli indicate that a closer relationship than the one observed was not prevented by a deficient reliability in the determination of one or both of these measures. Janal et al. (1994) suggested that only a correlation coefficient of at least 0.5 would justify to consider a test recording the sensitivity to one type of painful stimuli to be equivalent to a test recording the sensitivity to another type of stimuli. Thus, although patients with ano-
rexia and bulimia consistently have higher thresholds to thermally as well as to mechanically induced pain than healthy subjects, it is not yet clear whether an increased threshold in one modality can be interpreted as indicative for an increased threshold also in another modality and for a generally lower pain sensitivity in individuals suffering from these eating disorders. Moreover, techniques used for the determination of the thresholds at which stimuli of differing nature are perceived as painful are prone to yield results influenced, to varying and difficult to evaluate degrees, by factors not related to pain perception. Consequently, comparisons between the results of studies which employed different techniques and different stimuli have to be carried out with caution. Further investigations will be necessary to define factors of the above type and their impact for the determination of thresholds to thermal and mechanical as well as to other noxious stimuli on the one hand, and to reveal the mechanisms underlying the decreased pain sensitivity in patients with eating disorders on the other.
Acknowledgements
This study was supported by a research grant to Martina de Zwaan, M.D. from the Osterreichische Nationalbank (No. 4643), Vienna.
References Clark, J.W. and Bindra, D., Individual differences in pain thresholds, Can. J. Psychol., 10 (1956) 69-76. Faris, P.L., Raymond, N.C., de Zwaan, M., Howard, L.A., Eckert, E.D. and Mitchell, J.E., Nociceptive, but not tactile, thresholds are elevated in bulimia nervosa, BioI. Psychiatry, 32 (1992) 462-466. Harris, G. and Rollmann, G.B., The validity of experimental pain measures, Pain, 17 (1983) 369-376. Janal, M.N., Giusman, M., Kuhl, J.P. and Clark, W.e., On the absence of correlation between responses to noxious heat, cold, electrical and ischemic stimulation, Pain, 58 (1994) 403-411. Lautenbacher, S., Pauls, A.M., Strian, F .. Pirke, K.-M. and Krieg. J.-C., Pain perception in patients with eating disorders. Psychosom. Med., 52 (1990) 673-682. Lautenbacher. S .• Pauls, A.M., Strian, F., Pirke, K.-M. and Krieg, J.-C., Pain sensitivity in anorexia nervosa and bulimia nervosa. BioI. Psychiatry, 29 (1991) 1073-1078. Lynn, B. and Peri, E., A comparison of four tests for assessing the pain sensitivity of different subjects and test areas, Pain, 3 (1977) 363365. Stacher, G., Steinringer, H., Schneider, C., Mittelbach, G., Winklehner, S. and Gaupmann, G., Experimental pain induced by electrical and thermal stimulation of the skin in healthy man: sensitivity to 75 and 150 mg diclofenac sodium in comparison with 60 mg codeine and placebo, Br. J. Clin. Pharmacol., 21 (1986) 35-43.
511
PAIN 3143
Clinical note Relationship between thresholds to thermally and to mechanically induced pain in patients with eating disorders and healthy subjects 1 Martina de Zwaana,*, Dagmar Bienera , Christa Schneiderb and Georg Stacherb aDivision of General Psychiatry, Department of Psychiatry and bpsychophysiology Unit, Department of Surgery, University of Vienna, Vienna (Austria)
(Received 22 August 1995, revised version received 16 March 1995, accepted 21 March 1996)
Summary
This paper presents the results of a correlation analysis comparing thresholds to thermally and to mechanically induced pain in 40 patients with eating disorders and 32 healthy control subjects. The correlation coefficients for the response to the two modalities of pain were 0.498 for the whole sample, 0.430 for the healthy subjects, and 0.402 for the patients with eating disorders. Although these results indicate a significant overlap in the individuals' responses to the two modalities of induced pain, the criterion suggested by Janal et al. (Pain, 58 (1994) 403-411) of a 'minimum correlation of 0.5 (that) would justify allowing one test to be considered equivalent to another' is not met.
Key words: Threshold to mechanically induced pain; Threshold to thermally induced pain; Anorexia nervosa; Bulimia nervosa
Introduction The relationship between the responses of humans to painful stimuli of different nature has been investigated in a small number of studies only. In 45 men, thresholds to pain induced by radiant heat, pressure, and electrical stimulation were found to be highly related (Clark and Bindra 1956). Similarly, thresholds to pain induced by the immersion of an arm into ice water, pressure, and electrical stimuli correlated significantly in 40 healthy subjects (Harris and Rollmann 1983). By contrast, in 24 healthy men exposed to heat, cold, pinch, and pinprick stimulation, only the thresholds to pain induced by heat and pinching were interrelated significantly (Lynn and Perl 1977). Janal et al. (1994) found near-zero correlations between measures of the sensitivity to noxious heat, cold, ischemic, and electrical laboratory pain in healthy volunteers as well as in patients with coronary artery disease. The present study was aimed at investigating the relationship between the thresholds to thermally and to mechanically induced pain in healthy
*
Correspondmg author: Martina de Zwaan, MD., Division of General Psychiatry, Department of Psychiatry, UnivefSlty of Vienna, Wiihnnger Gtirtel 18-20, A-1090 Vienna, Austria. I Part of the data gathered is contained in a paper accepted for publication in the Journal of Psychosomatic Research.
PI/ S0304-3959(96)03143-0
subjects as well as in patients with anorexia nervosa and bulimia nervosa. In patients with both eating disorders, thresholds to thermally (Lautenbacher et al. 1990, 1991) and to mechanically (Faris et al. 1992) induced pain have been found to be elevated.
Methods Thresholds to pain induced by thermal and mechanical stimulation were determined in 40 female patients hospitalized for the treatment of eating disorders, i.e. in 22 patients with anorexia nervosa and in 18 with bulimia nervosa, as well as in 32 healthy subjects of comparable age. Thresholds to mechanically induced pain were assessed using an Ugo Basile Analgesymeter (Ugo Basile, Biological Research Apparatus, Comerio, VA, Italy). Pressure stimuli were applied sequentially to the tips of digits II-V of the subjects' non-dominant hand using a motorized drive. The pressure exerted increased from 0 to a maximum of 1260 gat a rate of 80 gls. Subjects were instructed to press a button when they first perceived the pressure as painful. Thresholds to thermally induced pain were measured in response to radiant heat stimuli of constant intensity. Sequentially, eight different sites on the volar surface of the subjects' non-dominant forearms were exposed to the stimulus. The subjects were instructed to withdraw their forearm from the stimulator as soon as they perceived the heat stimulus as painful and thereby to indicate their pain threshold (Stacher et aI., 1986). In the analysis, the eight threshold values recorded in each individual were averaged. In the 32 healthy subjects, the test-retest reliability of the techniques to assess the thresholds to mechanically and thermally induced pain was determined by performing another series of measure-
512 TABLE I CHARACTERISTICS OF, AND DATA GATHERED IN, THE PATIENTS WITH EATING DISORDERS AND THE HEALTHY SUBJECTS (MEANS ± SD)
Age (years) Body mass index (kglm 2) Threshold to mechanically induced pain (g) Threshold to thermally induced pain (ms)
Patients (n = 40)
Healthy subjects (n 32)
22.9 ± 4.5 175±3.7 668.6 ± 237.6
24.0 ± 3.6 22.3 ± 3.6* 496.4 ± 169.4*
3108±691
2597 ± 465*
=
*t-test for sample means, P < 0.001.
ments 7 days after the first testing. The study was approved by the Ethical Committee of the Faculty of Medicine, University of Vienna.
Results
The mean thresholds to mechanically induced pain were significantly related to the mean thresholds to thermally induced pain (Pearson product-moment correlation: overall, r(70) = 0.498, P < 0.001; healthy subjects, r(30) = 0.430, P < 0.014; and patients, r(38) =0.402, P < 0.01). Thresholds to mechanically as well as to thermally induced pain differed significantly between the patients with eating disorders and the healthy subjects: the patients had significantly higher thresholds for both mechanically (t-test for sample means, t(70) =3.45, P < 0.001) and thermally induced pain (t(70) =3.58, P < 0.001; Table I). The testretest reliability for the threshold to mechanically induced pain as well as for the threshold to thermally induced pain was high (r(30) = 0.709, P < 0.001, and r(30) = 0.663, P < 0.001, respectively).
Discussion
The results show that, in the patients with eating disorders as well as in the healthy subjects, the thresholds to mechanically induced pain correlated significantly with the thresholds to thermally induced pain. The high test-retest reliabilities found in the healthy subjects for the thresholds to the two types of noxious stimuli indicate that a closer relationship than the one observed was not prevented by a deficient reliability in the determination of one or both of these measures. Janal et al. (1994) suggested that only a correlation coefficient of at least 0.5 would justify to consider a test recording the sensitivity to one type of painful stimuli to be equivalent to a test recording the sensitivity to another type of stimuli. Thus, although patients with ano-
rexia and bulimia consistently have higher thresholds to thermally as well as to mechanically induced pain than healthy subjects, it is not yet clear whether an increased threshold in one modality can be interpreted as indicative for an increased threshold also in another modality and for a generally lower pain sensitivity in individuals suffering from these eating disorders. Moreover, techniques used for the determination of the thresholds at which stimuli of differing nature are perceived as painful are prone to yield results influenced, to varying and difficult to evaluate degrees, by factors not related to pain perception. Consequently, comparisons between the results of studies which employed different techniques and different stimuli have to be carried out with caution. Further investigations will be necessary to define factors of the above type and their impact for the determination of thresholds to thermal and mechanical as well as to other noxious stimuli on the one hand, and to reveal the mechanisms underlying the decreased pain sensitivity in patients with eating disorders on the other.
Acknowledgements
This study was supported by a research grant to Martina de Zwaan, M.D. from the Osterreichische Nationalbank (No. 4643), Vienna.
References Clark, J.W. and Bindra, D., Individual differences in pain thresholds, Can. J. Psychol., 10 (1956) 69-76. Faris, P.L., Raymond, N.C., de Zwaan, M., Howard, L.A., Eckert, E.D. and Mitchell, J.E., Nociceptive, but not tactile, thresholds are elevated in bulimia nervosa, BioI. Psychiatry, 32 (1992) 462-466. Harris, G. and Rollmann, G.B., The validity of experimental pain measures, Pain, 17 (1983) 369-376. Janal, M.N., Giusman, M., Kuhl, J.P. and Clark, W.e., On the absence of correlation between responses to noxious heat, cold, electrical and ischemic stimulation, Pain, 58 (1994) 403-411. Lautenbacher, S., Pauls, A.M., Strian, F .. Pirke, K.-M. and Krieg. J.-C., Pain perception in patients with eating disorders. Psychosom. Med., 52 (1990) 673-682. Lautenbacher. S .• Pauls, A.M., Strian, F., Pirke, K.-M. and Krieg, J.-C., Pain sensitivity in anorexia nervosa and bulimia nervosa. BioI. Psychiatry, 29 (1991) 1073-1078. Lynn, B. and Peri, E., A comparison of four tests for assessing the pain sensitivity of different subjects and test areas, Pain, 3 (1977) 363365. Stacher, G., Steinringer, H., Schneider, C., Mittelbach, G., Winklehner, S. and Gaupmann, G., Experimental pain induced by electrical and thermal stimulation of the skin in healthy man: sensitivity to 75 and 150 mg diclofenac sodium in comparison with 60 mg codeine and placebo, Br. J. Clin. Pharmacol., 21 (1986) 35-43.