Pain threshold and pain tolerance as a predictor of deliberate self-harm among adolescents and young adults.

BACKGROUND: Recently, the assessment of pain has been used as a parameter to differentiate adolescents who indulge in deliberate self-harm from healthy individuals. AIMS AND
OBJECTIVES: The present study was conducted to compare pain sensitivity between three groups, i.e., nonsuicidal self-injury/nonsuicidal self-harm (NSSI), suicide attempters (SA), and matched healthy control (NSSI, SA, and healthy controls).
MATERIALS AND METHODS: Ninety participants (30-NSSI, 30-SA, and 30 matched control) between the age of 10 and 25 years were inducted from the individuals who came for help at the outdoor and emergency services for recent self-harm. Pain sensitivity was assessed by cold pain stimulation test through a cold pressor task.
RESULTS: Pain threshold, pain tolerance, total pain index as well as pain experience intensity were significantly different in the three groups.
CONCLUSION: Participants who indulge in NSSI and SA have significantly higher pain threshold, pain tolerance, total pain index, and pain experience intensity as compared to healthy control. Although all the pain parameters were higher in the NSSI group as compared to SA group, the difference did not reach to significant level. Copyright:

INTRODUCTION

Pain perception has been an area of interest among adolescents and young adults who indulge in deliberate self-harm. Many studies have found that individuals with borderline personality disorder (BPD) who engage in nonsuicidal self-injury/nonsuicidal self-harm (NSSI) experienced no pain during self-injuring.[123] Research has also shown that approximately 60% of persons with BPD and 80% of adolescent from psychiatric inpatients services reported little or no pain during NSSI.[45] There is also evidence that heightened pain tolerance was associated with suicidal risk and adolescents who reported the absence of pain during NSSI reported twice as many suicide attempts as compared to those who reported experiencing pain during NSSI.[6]

Researchers have attempted to find out why persons engage in self-harm and how they are able to overcome the instinct to feel pain. It has been suggested that individuals who engage in NSSI gradually become desensitized to pain through opponent processing.[7] Research has shown that diminished pain perception has been attributed to altered levels of endogenous opioids.[8910] There is also evidence that cerebrospinal fluid β–endorphin and met-enkephalin levels of endogenous opioids are significantly lower in patients with a history of NSSI.[10] It has been suggested that people engage in NSSI to regulate their emotions.[2] The clinicians and researchers have been trying to find out whether pain perception can be used as a marker that differentiates between NSSI and suicidal attempt. Although there are encouraging indications from Western studies, there is no work from India. The present study was conducted to compare pain sensitivity between three groups (NSSI, Suicide Attempters [SA], and healthy controls).

MATERIALS AND METHODS

This study was conducted on 90 participants (30-NSSI, 30-Suicide attempters, and 30 matched control) between the age of 10–25 years. The study participants were inducted from the patients who came for help at the outdoor and emergency services for recent self-harm (within the past 7 days). The participants with comorbid medical and neurological illness, intellectual disability, accidental injury, and history of suicidal attempt were excluded from this study. The age and sex-matched control was inducted from the caregivers of the patient who accompanied the patient to the hospital and there was no history of DSH and psychiatric illness. The consent was obtained from the legal representatives in case of minors and participants in the case of adults. The protocol was approved by the research and ethics committee of the institute.

The socio-demographic and clinical details were recorded on specially developed semi-structured pro forma routinely used in the department of psychiatry. NSSI was defined as the deliberate, self-inflicted destruction of body tissue or ingestion of a harmful chemical or ingestion of a chemical in excess, without suicidal intent, and for the purposes not socially sanctioned. Suicide Attempt was defined as self-directed, potentially injurious behavior with intent to die as a result of the behavior.[11]

For assessing pain sensitivity, all the 90 participants were assessed by cold pain stimulation test through a cold pressor task (CPT) procedure.[12] For this, all the participants were asked to immerse their hand up to the wrist in a tank filled with water. Water temperature of the CPT was kept at approximately 4°C and controlled constantly with the help of thermostat. Before the immersion, the participants were told to keep the hand in the water until cold pressure pain turns intolerable. The latencies to the first pain sensation (pain threshold) and to the intolerable pain (pain tolerance) were measured with a stopwatch in seconds. After the CPT, the participants were asked to fill in the short-form McGill Pain Questionnaire (Melzack R. The McGill Pain Questionnaire: major properties and scoring methods. Pain 1975; 1:277-99.) which consists of 15 descriptors (11 sensory and 4 affective) that are rated on a 4-point intensity scale from zero as none to three as severe.[13] The questionnaire was administered to all the participants immediately after the cold pressure task was over. The total pain index was measured by the sum of the two pain scores (sensory and affective) obtained by adding the intensity rank values of the words chosen for descriptors. The overall pain experience was assessed by one descriptor, i.e., no pain, mild discomforting, distressing, and horrible or excruciating.

RESULTS

Table 1 shows that pain threshold, pain tolerance, total pain index as well as pain experience intensity was significantly different in the three groups. Intergroup analysis revealed significantly higher pain threshold and pain tolerance in the two groups compared to the control group. NSSI groups had maximum pain threshold and pain tolerance values, i.e., 66 and 101 s, respectively, compared to 38 and 75 s in the SA group and 26 and 51 s in the control group.

Table 1

Pain threshold and pain tolerance of the participants

Parameters	NSSI (n=30)		SA (n=30)		Healthy controls (n=30)		χ2 (df)	P
	Mean	SD	Mean	SD	Mean	SD
Pain threshold (s)	65.97	70.50	37.87	19.80	26.20	13.03	16.48 (2)	0.000
Pain tolerance (s)	101.2	60.64	74.83	34.17	50.67	24.95	21.21 (2)	0.000
Total pain index	3.57	2.06	4.00	1.08	5.10	1.65	10.86 (2)	0.004
Pain experience intensity	1.87	1.008	2.47	0.68	2.73	0.69	11.86 (2)	0.003

NSSI – Nonsuicidal self-injury; SA – Suicide attempters; SD – Standard deviation

Similarly, total pain index and pain experience intensity were lower in the two groups compared to the control group. Total pain index was 3.6 (±2.1) and 4 (±1.1) in NSSI and SA group, respectively, compared to 5.1 (±1.6) in healthy controls. Pain experience intensity values were 1.87 (±1) and 2.47 (±0.7) compared to 2.73 (±0.7) in the control group.

Comparing the participants of NSSI with SA, no significant difference was found in pain threshold, tolerance, and total pain index among both the groups. However, pain experience intensity was significantly different between two groups [Table 2].

Table 2

Comparison between nonsuicidal self-injury and suicide attempters on pain experience (Mann-Whitney test)

Parameter	P
Pain threshold	0.118
Pain tolerance	0.082
Total pain index	0.440
Pain experience intensity	0.029@

@P<0.05

Table 3 shows that when the participants from NSSI group were compared with healthy control, there was significant difference between all the four parameters, i.e., pain threshold, pain tolerance, total pain index, and pain experience intensity.

Table 3

Nonsuicidal self-injury versus healthy controls (Mann-Whitney test)

Parameter	P
Pain threshold	0.000
Pain tolerance	0.000
Total pain index	0.004
Pain experience intensity	0.001

Similarly, when participants from SA group were compared with healthy control [Table 4], there was significant difference in pain threshold, pain tolerance, and total pain index. However, there was no difference in pain experience intensity. When pain parameters of NSSI and SA participants were compared, suicide attempters were compared separately with the control group.

Table 4

Suicide attempters versus healthy controls (Mann-Whitney test)

Parameters	P
Pain threshold	0.010
Pain tolerance	0.003
Total pain index	0.006
Pain experience intensity	0.147

DISCUSSION

The present study attempted to study pain perception as a biological marker to differentiate between NSSI, SA, and healthy control groups. The results showed significant difference in pain perception using cold pressure task between the three groups and the difference was evident on all the pain parameters, i.e., pain threshold, pain tolerance, total pain index, and pain experience intensity. Both the NSSI participants and SA reported a higher pain threshold and pain tolerance level than the controls. The participants in the two study groups also reported lower pain intensities compared to the control groups.

Earlier studies have also found that self-injurers had higher pain thresholds and pain tolerance than noninjurers during a cold pressor task.[31214] Another recent systematic review suggested that those who engage in self-harm without suicidal intent have an increased threshold and tolerance for pain.[15] In order to study whether impairment in pain parameters is a trait or state dependent, a study examined pain perception in those who had formerly engaged in NSSI, currently engaged in NSSI and healthy controls and found that those who currently engaged in NSSI had the highest pain threshold, followed by those who used to engage in NSSI and the healthy controls had the least pain threshold.[16] It has also been reported that higher pain tolerance occurs in response to a wide variety of pain modalities, including the CPT, pressure algometer, and electrical pain.[15] Although several psychological correlates of pain threshold and tolerance have been explored in this population, however, the results are sometimes contradictory. Thus, there is no clear consensus as yet regarding the underlying mechanism for altered pain tolerance in NSSI[15] and future research is required to explore this area using large epidemiological studies.

Limitations

Although the present study was carried out using sound methodology, still the study has certain limitations. The study group may not be a true representative of the population as many cases avoid coming for treatment due to the fear of disclosure and legal consequences. Further, the patients were divided into two groups based on their self-report of intent, i.e., whether they engaged in self-harm with the intention of dying or without this intention and there was no objective tool to assess their intention before recruitment into the separate groups. Furthermore, the sample size was small and this might have limited the power to detect differences between the groups. Another limitation was lack of recording of the use of medication by the participants.

CONCLUSION

The participants who indulge in NSSI and SA have significantly higher pain threshold, pain tolerance, total pain index, and pain experience intensity as compared to healthy control. While comparing the NSSI and SA participants, although all the pain parameters were higher in the NSSI group as compared to SA group, the difference did not reach to significant level.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.