Kato et al. BioPsychoSocial Medicine (2017) 11:13
DOI 10.1186/s13030-017-0098-4

RESEARCH

Open Access

Pain threshold reflects psychological traits
in patients with chronic pain: a crosssectional study
Fumie Kato*, Tetsuya Abe, Kenji Kanbara, Ikumi Ban, Tadashi Kiba, Sadanobu Kawashima, Yukie Saka,
Yasuyuki Mizuno and Mikihiko Fukunaga

Abstract
Background: Chronic pain enhances sensory sensitivity and induces the biased development of psychological traits
such as depression and pain catastrophizing, leading to the formation of heterogeneous conditions. Fluctuations inthe sensory-related thresholds of non-injured sites (with normal peripheral tissue) in patients with chronic pain arethought to be related to central sensitization. The objectives of this study were to analyze the association between
pain tolerance thresholds (PTTs) in non-injured sites and the psychological traits of patients with chronic pain andto evaluate the usefulness of PTT measures in assessments of pathological conditions related to chronic pain.
Methods: This study included 57 patients with chronic pain. The PTTs were measured in non-injured sites withquantitative sensory testing (QST) with electrical stimulation and then classified with cluster analysis. The ShortForm McGill Pain Questionnaire was used to subjectively assess pain in the injured sites. The Minnesota Multiphasic
Personality Inventory (MMPI) was used to assess the patients’ psychological traits.
Results: Based on the cluster analysis of PTTs, the patients were classified into a High-Sensitivity group and an
Others group consisting of the remaining patients. The results of the MMPI profiles showed that the High-Sensitivity
group included significantly more patients with the Neurotic Triad pattern and no patients with the Conversion V
pattern. The scores of the hypochondriasis and hysteria scales were significantly lower in the High-Sensitivity groupthan in the Others group.
Conclusions: This study indicated that patients with chronic pain can be classified according to PTTs in non-injured
sites and suggests that patients with High-Sensitivity have characteristic psychological traits. Assessment of PTTs in
non-injured sites would be useful for evaluating the psychological condition of patients with chronic pain.
Keywords: Chronic pain, Pain tolerance threshold, Central sensitization, High sensitivity, Minnesota Multiphasic
Personality Inventory, Quantitative sensory testing

Background
Pain is defined as an unpleasant sensory and emotional
experience that is associated with actual or potential tissue damage or that is described in terms of such damage[1]. While assessments of both the associated sensations
and emotions are important for understanding pain,these methods are limited because perception of pain
differs among individuals and is affected by environmental and psychological factors at different times. In clinical* Correspondence: katofum@hirakata.kmu.ac.jp
Department of Psychosomatic Medicine, Kansai Medical University, 2-5-1
Shinmachi, Hirakata-shi, Osaka, Japanpractice, such traits related to pain make diagnosis andtreatment difficult and contribute to the development ofrefractory and chronic pain [2, 3].
Chronic pain refers to pain of no fixed duration extending beyond the expected period of healing or to pain
related to progressive non-cancer diseases [4]. As pathological conditions involve a combination of physical factors including tissue damage and psychosocial factors
such as alexithymia [5], pain catastrophizing [6, 7], anxiety [8], living standard, and lifestyle [9], classification ofthese pathological conditions that are based on particular diseases or the affected tissues are not always useful© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Kato et al. BioPsychoSocial Medicine (2017) 11:13

for understanding the pathological conditions or determining appropriate treatments. No methods with common physiological or psychological indicators have been
established to classify and evaluate patients with chronicpain.
The following three in vivo mechanisms transform
acute pain into chronic pain: peripheral sensitization
at the peripheral level, dysfunction of the descending
pain inhibitory system, and central sensitization at thecentral level [10–13]. These mechanisms not only enhance pain at sites of tissue damage but also frequently induce the appearance of spontaneous pain orchanges in the sensory sensitivity of non-injured sites
to stimulation [8, 14, 15].
Quantitative sensory testing (QST) is a noninvasive
method used to objectively assess subjective pain.
Specifically, QST assesses neural function by quantifying the sensory-related thresholds of the responses ofthe examinees to various experimental stimuli, suchas thermal, pressure, electrical, and ischemic stimuli[16–20]. The sensory-related thresholds at sites of injury are associated with the three in vivo mechanisms
described above, whereas fluctuations in the sensoryrelated thresholds of non-injured sites reflect only
mechanisms at the central level [17, 20]. Studies of
the QST of chronic pain have shown that pain
thresholds decrease at non-injured sites in female patients with non-traumatic neck-shoulder pain and patients with unilateral epicondylalgia [10, 21]. The
results of these studies suggest that central sensitization
causes fluctuations in the pain thresholds of non-injured
sites in patients with chronic pain, regardless of their condition. Other previous studies suggest that QST is usefulfor classifying patients with chronic pain and for predicting treatment response [22–25].
Many studies have referred to the psychologicaltraits of patients with chronic pain. These traits include alexithymia, catastrophizing, anxiety, and depression [5–7, 26–28]. Although it is easy to administer
the self-reported questionnaires used to assess psychological traits in these studies, such as the Toronto
Alexithymia Scale, the 36-item Short-Form Health
Survey’s Mental Health Scale, and the Pain Catastrophizing Scale, the scales are based on subjective assessments
performed by patients and do not include items regarding
patient personality. The Minnesota Multiphasic Personality Inventory (MMPI) enables assessment of personality
from various perspectives and can be used for screening
for mental disorders. As this questionnaire includes validity scales, it is more likely to evaluate biased responses
than do other types of questionnaires [29, 30]. The MMPI
has been used to classify the psychological traits of patients with chronic pain, and characteristic MMPI profiles
have been reported for these patients [31–34].

Page 2 of 9

Factors that have been reported to be associated withlow pain thresholds include physical variables, such as
the severity and duration of the pain and decreased
autonomic function [35, 36]. On the other hand, pain
thresholds have been reported to increase in patientswith depression [26–28]. Cruz-Almeida et al. classifyed
patients with chronic pain by using psychological variables and displayed unique sets of clinical pain and somatosensory characteristics [37]. According to thesereports, physical and psychological factors and which result in heterogeneous chronic pain is strongly associatedwith increasing or decreasing the pain thresholds andcomplicating the central sensitization.
Some patients with chronic pain are, however, resistant to psychological intervention [38, 39]. In order toevaluate the usefulness of pain threshold measures as atool for assessing heterogeneous pathological conditions
that involve chronic pain, this study aimed to clarify the
association between pain thresholds in non-injured sites
and the psychological traits of patients with chronicpain.

Methods
Participants

The participants were selected from 81 patients withchronic pain who had been admitted to the departmentof Psychosomatic Medicine of Kansai Medical University. Based on previous studies [40–42], the participants
were diagnosed with nonmalignant chronic pain that
had persisted for three or more months by attending
physicians with clinical experience in treating chronic
pain. The staff members of the Department of Psychosomatic Medicine are physicians, not psychiatrists, andthe chief complaints of almost all patients are their
physical symptoms. Patients with any of the following
criteria were excluded: (1) an age of 18 years or less, (2)extensive peripheral neuropathy, (3) pain in the nondominant hand, (4) opioid use, or (5) a diagnosis ofmajor depression, schizophrenia, or dementia. After exclusions, the data of 57 patients with chronic pain wasavailable for analysis. In accordance with the study
protocol approved by the ethics committee of Kansai
Medical University Hospital, written informed consent
was obtained from the participants.
Pain tolerance threshold (PTT) assessment

In this study, the QST was performed with a Neurometer CPT (Neurotron, Incorporated, Towson, MD,
USA). With this device, an electrical stimulus of either
250 or 5 Hz was selectively applied to Aδ primary afferent fibers, which transmit sharp pain, and C primary afferent fibers, which transmit dull pain. The QST was
performed in a quiet room at a comfortable temperature.
The participants sat on a chair and a stimulating

Kato et al. BioPsychoSocial Medicine (2017) 11:13

electrode was attached around the distal interphalangeal
joint of the fourth finger of the non-dominant hand. The
electrical stimulation current was increased from 0 to
9.99 mA at a set rate while the button on the device waspressed, and the current stopped when the button was
released. After the patients were informed that stimulation with the highest electrical current would not cause
tissue or other damage to the body, the participants thenoperated the device by themselves. They were instructed
to release the button when the stimulus reached an unbearable level of pain, and this was defined as the PTT.
The QST was performed once for each level of stimulation, and measurements were taken every 30 s. Previous
studies have shown only a small level of variation among
measurements [43–45].
Assessment of pain intensity

Subjective assessments of the pain were performed with
the Short-Form McGill Pain Questionnaire (SF-MPQ).
The participants evaluated the pain with 15 expressions
that described the sensations and the emotions of pain,
which were rated on a 4-point scale, while the severityof the pain was evaluated with both a visual analog scale(VAS) and the Present Pain Intensity 6-point scale. The
reliability of the Japanese version of the SF-MPQ has
been confirmed [46].
Psychological instrument

The MMPI questionnaires were distributed to the participants before the experiment and then collected at the

Page 3 of 9time of the PTT measurement. The MMPI, which is aself-reported questionnaire on personality, is highly reliable for less invasively evaluating psychological traits
from various perspectives. The MMPI consists of four
validity scales (cannot say, lie, infrequency, and defensiveness) and ten clinical scales: Hypochondriasis (Hs),Depression (D), Hysteria (Hy), Psychopathic deviate,
Masculinity/femininity, Paranoia, Psychasthenia, Schizophrenia, Hypomania, and Social introversion that areassessed with 550 questions that are answered on a 3
point scale (agree, disagree, and neither). The scores arecalculated by assigning two points to agree and one
point to neither. Higher scores indicate a greater tendency for that trait. The results are expressed as numerical values and profile forms [29, 30].
In Japan, the MMPI has been widely used in the clinical and academic fields [47–49]. In the United States,
the transition to the MMPI-2 has already been completed. The basic scales of the MMPI are compatible
with those of the MMPI-2, and the items considered important in the clinical and academic fields are common
between the two versions. Thus, the assessment results
are considered similar for the MMPI and MMPI-2.
Statistical analysis

All values are presented as mean ± standard deviation(SD). The statistical analyses were performed on the dataof the 57 participants (22 male and 35 female). According to the scatter diagrams of the PTTs to the 250-Hz
and 5-Hz stimuli (Fig. 1), the PTTs were not distributed

Fig. 1 Scatter plot of the PTTs of the participants. Each circle represents one patient. A cluster analysis conducted with Ward’s method indicatedthat the Others group had higher PTTs than the High-Sensitivity group. PTT, pain tolerance thresholdKato et al. BioPsychoSocial Medicine (2017) 11:13

Page 4 of 9evenly among the patients with chronic pain. Therefore,a cluster analysis (Ward’s method) was performed with
PTTs as a variable of interest to extract a characteristic
group. Inter group comparisons were performed with at-test, one-way analysis of variance (ANOVA), χ2 test, or
residual analysis. The SPSS software program (version
11.5, IBM Corporation, Armonk, NY, USA) was used forthe analyses.

Results

Cluster analysis of the PTTs

The cluster analysis done to create the High-Sensitivity
group selected 23 participants with decreased PTTs (n =23) (Fig. 1). The PTTs ranged from a minimum of0.75 mA to a maximum of 3.00 mA. In contrast, thePTTs of the remaining participants were distributed in awide range, from a minimum of 1.60 mA to a maximumof 9.99 mA. Since we thought it was not appropriate todescribe the rest as a group with identical characteristics, this group was named Others (n = 34).

Demographic and clinical characteristics of the patients

Of the participants, 61.4% were female. The mean age
was 47.7 years, with a SD of 17.5 years. The mean pain
duration was 59.3 months, with a SD of 75.0 months(Table 1). The main diagnosis was Chronic pain (40%),
followed by Functional dyspepsia (10%), Fibromyalgia
syndrome (9%), and Premenstrual syndrome (9%). The
main sites of pain were the upper and low back (26%),
the lower extremities (23%), the abdomen (16%), and theneck (14%) (Table 2). The SF-MPQ scores were 15.30 ±7.78 for the sensory components and 6.00 ± 3.60 for theaffective components, while current pain intensity was
rated as 3.38 ± 1.21 on a six point scale ranging from 0(no pain) to 5 (unbearable pain). The severity of pain at
the injured site in the past week was rated as 6.71 ±2.50 cm on a 10-cm VAS (Table 1).

Comparison of the demographic and clinicalcharacteristics of the groups

Of the participants in the High-Sensitivity group 78.2%
were female, as were 50.0% of the participants in the
Others group. A χ2 test showed that the male-to-female
ratio did not differ between the groups. The mean ± SD
ages were 56.30 ± 15.83 years in the High-Sensitivity
group and 41.94 ± 16.35 years in the Others group. The
mean ± SD pain durations were 40.60 ± 76.42 months in
the High-Sensitivity group and 73.23 ± 81.90 months in
the Others group. The t-tests showed that neither age
nor pain duration differed between the groups. In
addition, t-tests showed that the scores on the sensitive
and affective components of the SF-MPQ, VAS scores,
and current pain ratings did not differ between thegroups (Table 3).

PTT

The PTTs to 250-Hz stimulus ranged from 0.80 mA to
9.99 mA, with a mean ± SD of 4.59 ± 3.00 mA. The PTTs
to 5-Hz stimulus ranged from 0.75 mA to 9.99 mA, witha mean ± SD of 4.23 ± 2.93 mA.
The mean ± SD PTTs to 250-Hz stimulus were 5.74 ±3.19 mA for male and 3.87 ± 2.67 mA for female participants, while those to 5-Hz stimulus were 5.53 ± 3.19 mA
and 3.41 ± 2.47 mA, respectively. The PTTs to both
stimuli were significantly lower for female participants(250 Hz, p < 0.05; 5 Hz, p < 0.01).
Table 1 Patient characteristics
Variablesn = 57 (Female, 61.4%)
Mean

SD

Age (y)

47.75

17.51

Pain Duration (m)

59.33

73.00

250 Hz PTT (mA)

4.59

3.00

5 Hz PTT (mA)

4.23

2.93

SF-MPQ sensory score

15.30

7.78

SF-MPQ affective score

6.00

3.60

SF-MPQ Visual Analog Scale

6.71

2.50

SF-MPQ Present Pain Intensity

3.38

1.21

SD standard deviation, PTT pain tolerance threshold, SF-MPQ Short-Form McGill
Pain Questionnaire

Comparison of the MMPI clinical scales of the highsensitivity and the others groups

In the MMPI profiles, both groups showed high values
on the Hs, D, and Hy, scales (t ≥ 70), which are typicalprofiles for patients with chronic pain (Fig. 2). Patientswere classified by three patterns of these three scales:
Conversion V pattern, in which the scores on the Hs
and Hy scales were higher than the score on the D scaleby 10 or more points; the Neurotic Triad pattern, in
which the scores on the Hs and Hy scales were lower
than the score on the D scale; and the others patterns.
The High-Sensitivity group contained no participants
with the Conversion V pattern, 11 with the Neurotic
Triad pattern, and 12 with other patterns, whereas the
Others group contained 17, 7, and 10 participants ineach of these categories, respectively (Table 4). A χ2 test
(Yates’ correction) showed that the distribution of thesepatterns differed significantly between the groups. The
residual analyses showed that the proportion of participants with the Conversion V pattern was significantly
lower in the High-Sensitivity group, while the Neurotic
Triad pattern was significantly higher (p < 0.01 for both).
No significant difference in the proportions of the participants with the other patterns was observed.

Kato et al. BioPsychoSocial Medicine (2017) 11:13

Page 5 of 9

Table 2 The prevalence of each diagnosis and pain location
Diagnosis categories%

Pain location%

Chronic pain40

Low back26

Functional dyspepsia

10

Lower extremities (both/each)

23

Fibromyalgia syndrome

9

Abdomen16

Premenstrual syndrome

9

Neck

14

Irritable bowel syndrome

4Shoulder (both/each)

10

Spinal canal stenosis

4

Back

9

Herniated intervertebral disc, Splenic flexure syndrome, Combined headache, Tension
headache, Chronic pancreatitis, Oral malaisis, Dysautonomia, Functional somatic syndrome

Epigastric region, Whole body, Half body,Head, Hypochondrial region, Buttocks, Chest,
Upper arm(both/each)

males and females. For instance, Fernández-Carnero etal. studied hyperalgesia in patients with unilateral epicondylalgia and reported that the pain threshold for experimental pain was lower in female than in malepatients [21], and Kindler et al. studied the sensitivity toexperimental and clinical pain in patients with shoulder
pain and reported that females were more sensitive toboth types of pain [50]. Our results supported these previous results.
Age was significantly higher in the High-Sensitivity
group compared to that in the Others group. Previous
studies have shown that aging is associated with an increase in pain perception threshold and a decrease in
PTT, and this has been attributed to aging-induced impairments in both the excitatory and inhibitory functionsin the mechanisms underlying pain perception [51]. The
results obtained in the present study were similar to theresults of these studies.
Although the pain duration of the participants did not
differ between the High-Sensitivity and the Others
groups, the pain duration varied widely, from 3 months
to 240 months. While pain duration has been reported
to be longer in patients with the Conversion V pattern[52], our results showed that some patients with long

Moreover, the scores on the MMPI clinical scales werecompared with a one-way ANOVA. The scores on theHs and Hy scales were significantly lower in the HighSensitivity group than in the Others group (p < 0.05 forboth) (Table 5).

Discussion
This study aimed to examine the relationship between
the PTTs and psychological traits of patients withchronic pain in order to evaluate the usefulness of pain
thresholds for assessing the pathological conditions ofpatients with chronic pain.
In this study, the PTT, which is an indicator of central
sensitization, was measured in non-injured sites in patients with chronic pain. This study had two important
findings: these measurements differentiated a HighSensitivity group of patients who showed substantial decreases in their PTTs, and assessment with the MMPI
revealed psychological traits that were characteristic of
the patients with chronic pain, some of which have beenreported by previous studies.
In this study, the PTT was significantly lower in female participants. Several previous studies on sex difference have shown that pain sensitivity differs between
Table 3 Characteristics of the high-sensitivity and the others groups
Variables

High-Sensitivity (n = 23)

Others (n = 34)

Female, 78.2%

Female, 50.0%
Mean

SD

p

Age (y)

56.35

15.83

41.94

16.35

0.00**

Pain Duration (m)

40.61

76.48

73.23

81.90

0.10

250 Hz PTT (mA)

0.99

0.56

6.36

2.66

0.00**

5 Hz PTT (mA)

1.59

0.54

6.01

2.51

0.00**

SF-MPQ sensory score

13.91

7.98

16.29

7.61

0.27

SF-MPQ affective score

6.42

3.76

5.71

3.53

0.51

SF-MPQ Visual Analog Scale

7.12

2.36

6.43

2.60

0.32

SF-MPQ Present Pain Intensity

3.55

1.26

3.26

1.18

0.40

Mean

SD

Test of significance by independent t-test
SD standard deviation, PTT pain tolerance threshold, SF-MPQ Short-Form McGill Pain Questionnaire**p < 0.01

Kato et al. BioPsychoSocial Medicine (2017) 11:13

Page 6 of 9

Table 5 Comparison of the MMPI clinical scales
MMPI
clinicalscalesHs

Fig. 2 Line graphs of the t-scores for the clinical scales on the MMPI.
The MMPI score profiles were compared between the High-Sensitivity(n = 23) and Others (n = 34) groups (one-way analysis of variance; Hs
scale: F, 6.505; p, 0.014; Hy scale: F, 5.997; p, 0.018). MMPI, Minnesota
Multiphasic Personality Inventory; Hs, Hypochondriasis; D, Depression;Hy, Hysteria; Pd, Psychopathic deviate; Mf, Masculinity-femininity; Pa,
Paranoia; Pt, Psychasthenia; Sc, Schizophrenia; Ma, Hypomania; Si,
Social introversion

pain duration were in the Others group, which included
many patients with the Conversion V pattern. An inverse correlation between pain duration and pain thresholds has also been reported [20]. Further studies arenecessary to determine the association between pain
duration and various factors.
Classification of patients with chronic pain according to
PTTIn this study, patients with chronic pain were classified
using cluster analysis of the PTT at non-injured sites
and their psychological traits were evaluated. As a result,we identified a characteristic High-Sensitivity group.
Several previous studies done to classify patients withchronic pain have suggested a relationship between pain
Table 4 The number of subjects with the three Hs-D-Hy scalepatterns
Hs-D-Hy scale patterns

GroupHigh-sensitivity (n = 23)

Others (n = 34)

Conversion V pattern (%)

0 (0)17**(100)

Neurotic Triad pattern (%)

11** (61)

7 (39)

Other patterns (%)

12 (56)

10 (45)

Test of significance by χ2 test (Yates’ correction)
Hs hypochondriasis, D depression, Hy hysteria**p < 0.01

Group
High-sensitivity (n = 23)

Others (n = 34)

Mean

Mean

SD

F

p

81.91

14.49

6.500

0.014*

72.74

SD
11.42

D

74.70

13.58

74.38

10.80

0.009

0.923

Hy

72.43

12.30

80.18

11.29

5.997

0.018*

Pd

66.17

11.30

65.71

11.60

0.023

0.881

Mf

49.22

8.06

51.12

11.64

0.446

0.507

Pa

54.83

9.55

61.97

15.68

3.806

0.056

Pt

65.26

14.36

66.35

14.18

0.080

0.778

Sc

68.30

11.18

65.50

15.84

1.845

0.180

Ma

45.00

8.58

50.68

12.00

3.821

0.056

Si

54.09

10.56

55.15

11.32

0.127

0.723

Test of significance by one-way analysis of variance
Hs hypochondriasis, D depression, Hy hysteria, Pd psychopathic deviate, Mf
masculinity-feminity, Pa Paranoia, Pt psychasthenia, Sc schizophrenia, Ma
hypomania, Si social isolation*p < 0.05

and psychological traits. Murphy et al. showed that there
were multiple detectable subgroups of patients withchronic pain by cluster analysis of clinical pain intensityand psychological variables [53]. In addition, CruzAlmedia et al. classified patients with chronic pain bycluster analysis of psychological variables and clarified
the association between psychological characteristics andboth clinical pain intensities and pain thresholds [37].
Previous studies were classified according to psychological variables. In this study, we classified patients with chronic pain by cluster analysis with only
reproducible PTT as a physical variable to assess therelationship between psychological factors and PTTs.
The results strongly supported the study of CruzAlmedia et al., which showed close relationshipamong psychological traits, somatosensory sensations,and central sensitization to chronic pain [37]. Thisshows that patients with chronic pain can be classified by PTT as a physical variable.
Association between PTT and psychological traits

This study yielded results indicating an association between classifications based on PTTs and psychologicaltraits. Previous studies that used MMPI for patients withchronic pain found that their participants could be classified into three to six types [54–56], and the inclusionof the following three patterns is common to all of theseclassifications: the Conversion V pattern, the Neurotic
Triad, and the normal patterns, which show scoreswithin the normal range on all scales. The Conversion V
and the Neurotic Triad patterns are known MMPI profiles of patients with chronic pain, and they were foundfor 35 of the 57 participants observed, representing over

Kato et al. BioPsychoSocial Medicine (2017) 11:13

60% of our sample. Furthermore, the High-Sensitivity
group in this study included significantly more participants with the Neurotic Triad pattern than did the
Others group, but it did not include any participants
with the Conversion V pattern. Moreover, the scores on
the Hs and Hy scales in the High-Sensitivity group fellon the border between moderate and high scores andwere significantly lower than the ones in the Others
group. This indicates that the participants in the HighSensitivity group had different psychological traits fromother participants with chronic pain. The lack of any significant group-to-group difference in subjective pain intensity in this study suggested that, even though noapparent differences are detected in the severity of pain
reported by patients in clinical practice, their responses
to QST might imply their psychological traits. Thus, assessment of pain sensitivity using the QST, which focuses on the close association between pain thresholds
and psychological traits, may be particularly useful for
prediction of the psychological traits of patients withchronic pain who are resistant to psychological intervention, such as psychological testing.
Psychological traits of the high-sensitivity group

In this study, analysis of the MMPI showed that theHigh-Sensitivity group contained significantly more participants with the Neurotic Triad pattern, but none with
the Conversion V pattern. Moreover, the scores on theHs and Hy scales were significantly lower than those of
the Others group. The Conversion V pattern relates to acharacteristic profile of patients with chronic pain. Itshows the tendency to replace psychological problems
with physical complaints, and its socially incompatible
personality is also known to cause difficulties in treatment. On the other hand, the Neurotic Triad pattern ischaracterized by depressive tendency and hypochondriac
concerns [34]. While people with the Neurotic Triadpattern are introverted and nervous, previous studies
have shown that they are less likely to engage in selfharming [29, 30] and that they respond well tomultimodal treatment [57]. The Hs scale indicates ahypochondriac tendency, strong health concerns, andcatastrophizing. Those who show high scores on the Hs
scale tend to associate their normal physical sensations
with somatic symptoms. The characteristics of the Hy
scale are common to the Conversion V patterndescribed above. The above suggest that the HighSensitivity group has quite different psychological aspects than the Others group.
Limitations

In this study, data on income, social status, and working
conditions of the participants were not collected, andfurther studies with such data will be necessary. As

Page 7 of 9

ethnic differences have been suggested to affect assessment of psychological traits when using the MMPI, further studies with multiple ethnic groups are needed.
Since several reports have indicated that pain thresholds
are affected by hormonal levels during the cycle phases[58, 59] the subjects also need to be classified by sex foranalysis in future studies. Many patients with chronic
pain have depression, which is known to affect pain sensation; for this reason, these patients were excluded fromthe study, resulting in a smaller final sample size. Furthermore, the involvement of central sensitization canbe analyzed by measuring thresholds multiple times atmultiple points in unaffected tissue. This study was aclinical study, thus the results might have been affectedby the fact that the participants may not have been completely free from the effects of medication. However, no
studies have sufficiently described the effects of drugs,
such as nonsteroidal anti-inflammatory drugs and opioids, on QST [60, 61].

Conclusions
In this study, we were able to differentiate the patients
into a High-Sensitivity group by performing a cluster
analysis of PTTs to two types of pain stimuli that wereapplied to unaffected tissue in patients with chronic
pain. This High-Sensitivity group showed a significant
difference in the pattern and level of neurosis scales,
which is a characteristic MMPI profile of patients withchronic pain, different than the Others group. These results suggest that PTT would be a useful tool for understanding the psychological traits of patients with chronicpain.
Abbreviations
ANOVA: Analysis of variance; MMPI: Minnesota Multiphasic Personality
Inventory; PTT: Pain tolerance threshold; QST: Quantitative sensory testing;
SD: Standard deviation; SF-MPQ: Short-Form McGill Pain Questionnaire;
VAS: Visual analog scale
Acknowledgements
Not applicable.
Funding
This work was not supported by any external funding.
Availability of data and materials
The datasets used and/or analyzed during the current study available fromthe corresponding author on reasonable request.
Authors’ contributions
FK and TA designed the study and wrote the protocol. FK and TA collected
and entered the data. FK undertook the statistical analysis and wrote the firstdraft of the manuscript. All authors contributed to and have approved thefinal manuscript.
Competing interests
The authors declare that they have no competing interests.
Consent for publication
Not applicable.

Kato et al. BioPsychoSocial Medicine (2017) 11:13

Ethics approval and consent to participate
The Ethics Committee of the Kansai Medical University Hospital approved
the study protocol.

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.
Received: 26 December 2016 Accepted: 21 April 2017

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