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. Author manuscript; available in PMC: 2020 Sep 1.
Published in final edited form as: Nurs Res. 2019 Sep-Oct;68(5):365–373. doi: 10.1097/NNR.0000000000000375

Relationship of Pain Quality Descriptors and Quantitative Sensory Testing: Sickle Cell Disease

Brenda W Dyal 1, Miriam O Ezenwa 2, Saun-Joo Yoon 3, Roger B Fillingim 4, Yingwei Yao 5, Judith M Schlaeger 6, Marie L Suarez 7, Zaijie J Wang 8, Robert E Molokie 9, Diana J Wilkie 10
PMCID: PMC6715502  NIHMSID: NIHMS1531636  PMID: 31283720

Abstract

Background

Chronic pain in adults with sickle cell disease (SCD) may be the result of altered processing in the central nervous system as indicated by quantitative sensory testing (QST). Sensory pain quality descriptors on the McGill Pain Questionnaire (MPQ) are indicators of typical or altered pain mechanisms but have not been validated with QST-derived classifications.

Objectives

The specific aim of this study was to identify the sensory pain quality descriptors that are associated with the QST-derived normal or sensitized classifications. We expected to find that sets of sensory pain quality descriptors would discriminate the classifications.

Method

A cross-sectional quantitative study of existing data from 186 adults of African ancestry with SCD. Variables included MPQ descriptors, patient demographic data, and QST-derived classifications.

Results

The participants were classified as central sensitization (n = 33), mixed sensitization (n = 23) and normal sensation. Sensory pain quality descriptors that differed statistically between mixed sensitization and central sensation compared to normal sensitization included: cold (p = .01), and spreading (p=.01). Aching (p = .01) and throbbing (p = .01) differed statistically between central sensitization compared with mixed sensitization and normal sensation. Beating (p = .01) differed statistically between mixed sensitization compared with central sensitization and normal sensation. No set of sensory pain quality descriptors differed statistically between QST classifications.

Discussion

Our study is the first to examine the association between MPQ sensory pain quality descriptors and QST-derived classifications in adults with SCD. Our findings provide the basis for the development of an MPQ subscale with potential as a mechanism-based screening tool for neuropathic pain.

Keywords: central sensitization, McGill Pain Questionnaire, neuropathic pain, pain quality, pain quality descriptors, quantitative sensory testing

PAINReportIt® a computerized extension of the McGill Pain Questionnaire (MPQ), includes a subscale: The PAINReportIt® number of neuropathic pain words (PR-NNP). The PR-NNP is a screening tool for neuropathic pain in patients with sickle cell disease (SCD) but it lacks sufficient construct validity. The PR-NNP has only a moderate positive correlation (r = .41, r = .43, p = .001) with other neuropathic pain scales (Roach et al., 2016). The PR-NNP contains sensory pain quality descriptors that provide discrimination of pain type as well as differentiation between pain conditions (Campbell, Carroll et al., 2016; Campbell, Moscou-Jackson et al., 2016; Ezenwa et al., 2016; Melzack, 1975; Wilkie, Huang, Reilly, & Cain, 2001). The use of a standardized assessment tool to aid in the diagnosis of pain type could serve to decrease the use of opioid analgesics and reduce unnecessary treatment costs in patients with SCD (Bennett, Blair, Torrance, & Potter, 2005; Jensen, 2006; Roach et al., 2016; Wilkie et al., 2001). The purpose of this study was to identify the MPQ sensory pain quality descriptors that are associated with the quantitative sensory testing (QST)-derived sensitization response classifications in patients with SCD who experience chronic pain.

SCD is an inherited blood disorder that occurs in approximately 100,000 Americans, mainly of African descent (National Heart, Lung, and Blood Institute, 2017). Many adults with SCD can suffer from constant “chronic” pain, and results of recent studies reveal evidence of neuropathic pain in the SCD population (Campbell, Carroll et al., 2016; Campbell, Moscou-Jackson et al., 2016; Ezenwa et al., 2016; Molokie, Wang, & Wilkie, 2011; Wilkie et al., 2010). Neuropathic pain is pain resulting from nerve injury caused by a lesion or disease of the central (CNS) and/or peripheral (PNS) somatosensory nervous system (International Association for the Study of Pain, 2017). Even minor injury to the nerve can result in PNS and CNS changes that can lead to chronic pain (Dworkin et al., 2003). Neuropathic pain could result from increased responsivity of peripheral nociceptive afferents (e.g., peripheral sensitization) and/or increased excitability of neurons that transmit nociceptive information within the central nervous system (e.g., central sensitization; Darbani, Ballas, & Clauw, 2014; Woolf, 2011). The mechanisms of central sensitization are not well understood but are believed to result when innervation of central neurons cause permanent functional changes resulting in a state of hyperexcitability (Campbell & Meyer, 2006; Dworkin et al., 2003). Symptoms of central sensitization include hyperalgesia (an exaggerated pain response to normally painful stimulus) or allodynia (a painful response to normally nonpainful stimulus) and hyperalgesia occurring outside of the area of injury and continued pain sensation when the stimulus has ceased (Darbani et al., 2014; Woolf, 2011). Recent findings with QST indicate evidence of sensitization to thermal and mechanical stimuli in adults with SCD (Campbell, Carroll et al., 2016; Campbell, Moscou-Jackson et al., 2016; Ezenwa et al., 2016). Use of QST, however, requires a certain provider skillset together with the use of specialized equipment and normed values and, therefore, may not be feasible in all settings (Cruz-Almeida & Fillingim, 2014; Ezenwa et al., 2016; Rolke et al., 2006; Shy et al., 2003).

In a pilot study conducted with QST in adults with SCD, Ezenwa et al. (2016) found that 24 out of 25 adults with SCD had allodynia or hyperalgesia to thermal and mechanical stimuli. Other studies involving QST in patients with SCD reveal significantly increased heat sensitivity (lower heat pain thresholds) compared to their African American controls (Brandow, Stucky, Hillery, Hoffmann, & Panepinto et al., 2013; Campbell Moscou-Jackson et al., 2016; Ezenwa et al., 2016). Responses of adults with SCD to mechanical QST revealed abnormal sensitivity in the form of reduced mechanical pain thresholds compared to their African American controls (Ezenwa et al., 2016; Jacob et al., 2015; O’Leary, Crawford, Odame, Shorten, & McGrath, 2014).

It would be helpful if a self-report pain tool, such as the MPQ, could also accurately identify individuals with these abnormal sensory experiences. The MPQ was effective to discriminate between pain types in patients with trigeminal neuralgia and atypical facial pain and in lung cancer patients experiencing pain associated with neuropathic pain sites (Melzack, Torrence, Fromm, & Amsel, 1986; Wilkie et al, 2001). This previous research serves to demonstrate the potential of the MPQ for use in pain conditions. Problems with previous research include: (a) the finding that patients with neuropathic pain sites also selected pain quality words typically associated with nociceptive pain (Wilkie et al., 2001); and (b) researchers in previous studies relied upon clinical evaluation that may have included pain descriptors and patient health history for diagnosis of pain type (Melzack et al., 1986). Selection of nociceptive pain quality descriptors by patients with neuropathic pain can be indicative of the lack of specific verbal descriptors for pain type (Rasmussen et al., 2004) or could indicate incorrect diagnostic categorization (Boureau, Doubrère, & Luu, 1990). The concern with reliance upon clinical evaluation and patient health history for discrimination of pain type is that the results of physical examination are not well correlated with neurological disease pathology (Backonja, 2003). The use of pain quality descriptors provides discrimination of pain type as well as differentiation between pain conditions and is useful for researchers and clinicians in the diagnosis and treatment goals, and may serve to decrease the use of opioid analgesics and reduce unnecessary treatment costs in patients with SCD (Bennett et al., 2005; Jensen, 2006; Roach et al., 2016; Wilkie et al., 2001). Finding an association between the sensory pain quality descriptors on the MPQ and central sensitization versus normal sensory function with QST would demonstrate the discriminative value of the MPQ.

Avoiding pitfalls of the prior research, the specific aim of this study was to identify the MPQ sensory pain quality descriptors that are associated with the QST-derived classifications (central sensitization, mixed sensitization, normal sensation). We analyzed sets of sensory pain quality descriptors that, based on extensive evidence, were categorized as neuropathic and nociceptive quality descriptors. We expected to find that individual descriptors, sets of sensory pain quality descriptors, or both would correctly discriminate between patients classified by QST into sensitized versus normal sensation groups.

Methods

Design

This was a secondary analysis of a cross-sectional, single-session study that included 186 adults of African ancestry with SCD. The original study was approved by the University of Chicago at Illinois (UIC) institutional review board (IRB), and written signed consent of the participants was obtained. Approval to conduct the analysis of existing data was obtained from the University of Florida (UF) prior to request for the de-identified dataset.

Setting

The primary setting for collection of the data occurred at the UIC College of Nursing. UIC is a world-renowned center for the care of patients with SCD and has been instrumental in the development of policy and treatment for patients with SCD. The setting for the analysis of existing data was the UF College of Nursing.

Participants

The subjects were those who participated in the primary study. The target population for the primary study included current and new adult SCD patients who attended outpatient sickle cell clinics associated with University of Illinois Hospital and Health Sciences System (UIH). As SCD affects mainly those of African descent, recruitment targets included a sample of which 100% were from African descent, with intentional recruitment of male participants to achieve gender balance. Eligibility criteria required that the participant (a) was diagnosed with SCD; (b) had chronic SCD pain, defined as patient-reported pain > 0 on at least one half of the days for about three months during the previous 12 months; (c) was at least 18 years of age; (d) had moderate to severe pain level of pain (> 3 on 0–10 scale) within the last 12 months or currently on routine pain medications without which would have pain > 3; (e) reported African ancestry; and (f) was able to speak and read English. Exclusion criteria included patients who were (a) legally blind; (b) physically or cognitively unable to complete the study procedure; or (c) diagnosed with polyneuropathy or diabetes mellitus. Of the 186 participants, three were excluded from analysis due to missing QST classification and one was excluded from analysis due to missing MPQ sensory pain quality descriptors and missing demographics. Therefore, analysis included 182 participants.

Measurements

McGill Pain Questionnaire

The MPQ embedded within the computerized PAINReportIt® is a pain assessment tool useful for measuring patient’s pain perception with content validity for adults with SCD and test-retest reliability (Ezenwa et al., 2016; Jha et al., 2010; Wilkie et al., 2010; Wilkie, Savedra, et al, 1990). The MPQ includes 78 descriptors categorized into 20 sets of words that describe various dimensions of the pain experience (Melzack et al., 1986). Each category of sensory pain quality descriptors contains a group of words that are similar enough to fit into the same category but has subtleties that aid individuals in communicating their pain experiences (Melzack, 2005; Melzack, 1975). For our study, we examined the 54 sensory pain quality descriptors that can be further categorized as words that reflect neuropathic (28 words) or nociceptive (26 words) pain mechanisms (Wilkie et al., 2001). As they completed the PAINReportIt® assessment tool, patients were instructed to select the words that describe how their pain usually feels or its “nature.” Patients selected as many words as needed to describe how the pain feels. Some of the neuropathic sensory pain quality descriptors on the MPQ also appear on other neuropathic pain measures, such as the self-report version of the Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS) and the Neuropathic Pain Symptom Inventory (NPSI)—two valid neuropathic pain measures (Bennett et al., 2005; Bouhassira et al., 2004).

PAINReportIt® includes demographic questions regarding age, sex, marital status, education, income, and ethnicity, and the valid and reliable Pain Intensity Number Scale (PINS, 0 = no pain, 10 = pain as bad as it could be) as the measure for current pain and least and worst pain in the past 24 hours (Wilkie, Lovejoy et al., 1990).

Quantitative sensory testing

We did not use dynamic QST, which would test pain inhibition by including temporal summation (TS) and conditioned pain modulation (CPM; Granovsky & Yarnitsky, 2013). CPM response is not consistent across pain conditions (Julien, Goffaux, Arsenault, & Marchand, 2005; Kosek & Ordeberg, 2000), and are reduced in African Americans (Campbell et al., 2008) and in patients with SCD (Campbell, Carroll et al., 2016). Of particular importance in adults with SCD, the reduction in CPM response could be the result of long-term pain and the use of opioid agents (Harris et al., 2007; Ram, Eisenberg, Haddad, & Pud, 2008). Exploration of sensory parameters related to ascending fibers and not inclusive of descending tracts suited our purpose of identifying neural damage in adults with SCD (Granovsky & Yarnitsky, 2013). Based on our own concerns and those of the IRB about stimulating a SCD pain crisis during or following QST, we did not test TS or CPM. In an attempt to avoid a potential pain crisis, we used a QST protocol that was shown to be safe in adults with SCD and provide evidence of central sensitization (Ezenwa et al., 2016).

As found in previous research (Ezenwa et al., 2016) and basic pain mechanisms (Fields, Rowbotham, & Baron, 1998; von Hehn, Baron, & Woolf, 2012) the synthesis of QST findings for heat, cold, and mechanical pain thresholds at three sites (one not painful, two painful) provided the basis for classification of each adult with SCD (Ezenwa et al., 2016). Participants able to sense the stimuli and with negative QST findings for allodynia or hyperalgesia at all test sites were classified as having normal sensation. Positive QST findings for allodynia or hyperalgesia at nonpainful test sites resulted in participants classified with central sensitization. Participants were classified as peripheral sensitization with negative findings at the nonpainful test sites (A-beta, A-delta, and C) and positive A-delta or C-fiber findings at both pain sites. Participants that did not fit either central or peripheral sensitization or normal sensation criteria were classified as mixed sensitization. For this study, we were interested in understanding ascending peripheral fiber function and used this QST protocol to detect allodynia and hyperalgesia as potential indicators of neuropathic pain.

Analysis

Data were received in a de-identified electronic format so that privacy of the participants was maintained. Access to the electronic data was limited to the researchers who required access to perform analysis. Data were exported to IBM SPSS Statistics for Windows, version 25, for analytics. Descriptive statistics (mean, standard deviation, frequency) were generated. For each sensory pain quality descriptor, the proportion of positive responses was compared between the QST classifications using Fisher’s exact test. For each set of sensory pain quality descriptors, the proportion of positive responses was compared between the QST classifications using one-way analysis of variance (ANOVA). The level of significance was set at .05. As our study was an exploratory analysis to generate hypotheses to be tested through future study, we did not perform adjustments for the multiple tests.

Results

Sociodemographic Description of Participants

The participants with SCD were classified across the QST categories as follows: central sensitization 33 (18%), peripheral sensitization 1 (> 1%), mixed sensitization 23 (13%), and normal sensation 123 (69%). Due to missing response data for three of the participants and the one participant classified with peripheral sensitization, we focused on the 179 participants with variables of interest and classified as normal, mixed, or central sensitization in the following analysis. Among these 179 participants, most were female (60%), all were Black and/or African American (100%), but four of them also self-identified as multiracial and two as “other.” The participants also self-identified as non-Hispanic (98%), single or widowed (72%), and ranging in age between 19 to 66 years (M = 36.0, SD = 11.2; Table 1).

Table 1.

Demographic Characteristics of Participants and QST Classification

Variable Category Overall (n = 179) Central (33, 18%) Mixed (23, 13%) Normal (123, 68%) p-Value*
Age
(M=36.0 SD=11.2)		 19–39 years 117 (65) 17 (52) 16 (70) 84 (68) .20
40–66 years 62 (35) 16 (49) 7 (52) 39 (32)
Education High school or less 75 (42) 15 (46) 11 (48) 49 (40) .94
College/Vocational 72 (40) 12 (36) 9 (39) 51 (42)
Other/No Response 32 (18) 6 (18) 3 (13) 23 (19)
Race Black/African-American 173 (97) 31 (94) 22 (96) 120 (98) 1
Multi-race/Multi-ethnic 4 (2) 1 (3) 0 (0) 3 (2)
Other 2 (1) 1 (3) 1 (4) 0 (0)
Income $10,000 or less 74 (41) 19 (58) 10 (44) 45 (37) .12
More than $10,000 99 (55) 12 (36) 13 (57) 74 (60)
Other/No Response 6 (3) 2 (6) 0 (0) 4 (3)
Marital Married/partner 37 (21) 5 (15) 6 (26) 26 (21) .89
Single/Widowed 129 (72) 26 (79) 16 (69) 87 (71)
Other/No Response 13 (7) 2 (6) 1 (4) 10 (8)
Ethnicity Hispanic/Latino 4 (2) 1 (3) 1 (4) 2(2) .37
Not Hispanic/Latino 175 (98) 32 (97) 22 (99) 121 (98)
Sex Female 107 (60) 21 (64) 20 (87) 66 (54) .01
Male 72 (40) 12 (36) 3 (13) 57 (46)
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Note: Data are frequencies (percentages) unless otherwise specified; M = mean; SD = standard deviation.

*

Fisher’s exact test.

Participants’ Pain Experience Context

The number of neuropathic words selected by the adults with SCD ranged from 0 to 19 (M = 4.9, SD = 3.6), and the number of nociceptive words selected by adults with SCD ranged from 0 to 22 (M = 7.3, SD = 4.0). The number of sensory pain quality descriptors selected by participants ranged from 1 to 41 (M = 12.2, SD = 7.0). As a context for the amount of pain the participants experienced at the time of their other measures, the mean and standard deviation for participants’ current pain intensity was M = 3.8, SD = 2.9, least pain intensity in the past 24 hours was M = 3.3, SD = 2.5, and worst pain intensity in the past 24 hours was M = 5.9, SD = 3.1. There was a statistically significant difference in current pain intensity by classification groups [F (2, 176) = 3.62, p = .03] and a statistically significant difference in least pain intensity by classification groups [F (2, 176) = 4.59, p = .01]. A Tukey post hoc test revealed the mean current pain intensity was higher in the central sensitization group (M = 4.8, SD = 2.8) compared to the normal sensation group (M = 3.4, SD = 2.8, p = .04). Similarly, the least pain intensity in the past 24 hours was higher in central sensitization group (M = 4.2, SD = 2.1) compared to the normal sensation group (M = 3.1, SD = 2.5, p = .03). There were no other significant differences in pain intensity scores by QST classification.

Bivariate Analyses

Bivariate associations between the sensory pain quality descriptors (selected/not selected) and the QST-derived classifications (central sensitization, mixed sensitization, and normal sensation to mechanical and thermal QST) were evaluated using Fishers exact test (Table 2). Frequencies and percentages were used to describe the distributions of the 54 sensory pain quality descriptors across the QST-derived classifications. Analysis of each of the 54 sensory pain quality descriptors revealed that five sensory pain quality descriptors (aching, beating, cold, spreading, throbbing) differed significantly by QST classification (Table 2). Of the descriptors indicative of nociceptive pain, throbbing was selected by a larger proportion of the mixed sensitization group and the normal sensation group a lower proportion of the central sensitization group, and beating was selected by a larger proportion of the mixed sensitization group and a lower proportion of the central sensitization group and normal sensation group. Of the descriptors indicative of neuropathic pain, cold was selected by a larger proportion of the central and mixed sensitization groups and a lower proportion of the normal sensation group; and spreading was selected by a larger proportion of the mixed and central sensitization groups and a lower proportion of the normal sensation group. Aching was selected by a larger proportion of the mixed sensitization group and the normal sensation group and a lower proportion of the central sensitization group.

Table 2.

Sensory Quality Descriptors with QST Classification

Selected Word Overall (n=179) Central (33, 18%) Mixed (23, 13%) Normal (123, 68%) p-Value*
Aching 139 (78) 19 (58) 20 (87) 100 (81) .01
Boring 7 (4) 3 (9) 1 (4) 3 (2) .12
Burning 31 (17) 8 (24) 5 (22) 18 (15) .31
Cold 17 (10) 7 (21) 4 (17) 6 (5) .01
Cool 14 (9) 5 (15) 2 (9) 7 (6) .19
Drawing 3 (2) 1(3) 0 (0) 2 (2) .68
Drilling 23 (13) 6 (18) 3 (13) 14 (11) .54
Flashing 23 (13) 3 (9) 5 (22) 15 (12) .36
Flickering 12 (7) 1 (3) 0 (0) 11 (9) .30
Freezing 10 (6) 2 (6) 3 (13) 5 (4) .17
Hot 35 (20) 6 (18) 6 (26) 23 (19) .68
Itchy 24 (13) 6 (18) 3 (13) 15 (12) .63
Jumping 29 (16) 6 (18) 5 (22) 18 (15) .55
Lancinating 2 (1) 1 (3) 0 (0) 1 (1) .53
Numb 33 (18) 8 (24) 3 (13) 22 (18) .58
Penetrating 51 (29) 9 (27) 9 (39) 33 (27) .47
Pricking 18 (10) 4 (12) 4 (17) 10 (8) .29
Quivering 10 (6) 1 (3) 1 (4) 8 (7) .88
Radiating 39 (22) 6 (18) 7 (30) 26 (21) .53
Scalding 5 (3) 2 (6) 1(4) 2 (2) .23
Searing 10 (6) 3 (9) 2 (9) 5 (4) .31
Shooting 86 (48) 11 (33) 15 (65) 60 (49) .06
Smarting 3 (2) 0 (0) 0 (0) 3 (2) 1
Spreading 52 (29) 15 (46) 10 (44) 27 (22) .01
Stabbing 83 (46) 17 (56) 12 (52) 54 (44) .63
Stinging 23 (13) 7 (22) 5 (23) 11(9) .06
Tight 63 (35) 14 (42) 6 (26) 43 (35) .46
Tingling 39 (22) 10 (30) 4 (17) 25 (20) .41
Beating 63 (35) 7 (21) 14 (61) 42 (34) .01
Cramping 64 (36) 13 (39) 10 (44) 41 (34) .55
Crushing 41 (23) 8 (24) 6 (26) 27 (22) .89
Cutting 23 (13) 4 (12) 4 (17) 15 (12) .74
Dull 29 (16) 4 (12) 4 (17) 21 (17) .82
Gnawing 16 (9) 4 (12) 1 (4) 11 (9) .67
Heavy 52 (29) 9 (27) 10 (44) 33 (27) .26
Hurting 115 (64) 21 (33) 17 (74) 77 (63) .62
Lacerating 2 (1) 1 (3) 0 (0) 1 (1) .53
Piercing 45 (25) 5 (15) 9 (39) 31 (25) .14
Pinching 29 (16) 5 (15) 3 (13) 21 (17) .95
Pounding 93 (52) 12 (36) 16 (70) 65 (53) .05
Pressing 48 (27) 9 (27) 6 (26) 33 (27) 1
Pulling 33 (18) 9 (27) 5 (22) 19 (15) .25
Pulsing 69 (38) 11 (33) 8 (35) 50 (41) .73
Rasping 7 (4) 3 (9) 0 (0) 4 (3) .20
Sharp 141 (79) 26 (79) 20 (87) 95 (77) .67
Sore 91 (51) 17 (52) 15 (65) 59 (48) .32
Splitting 21 (12) 6 (18) 2 (9) 13 (11) .42
Squeezing 39 (22) 6 (18) 5 (22) 28 (23) .89
Taut 8 (5) 0 (0) 1 (4) 7 (6) .45
Tearing 22 (12) 4 (12) 5 (22) 13 (11) .29
Tender 68 (38) 8 (24) 13 (57) 47 (38) .05
Throbbing 138 (77) 20 (61) 22 (96) 96 (78) .01
Tugging 11 (6) 2 (6) 2 (9) 7 (6) .81
Wrenching 32 (18) 5 (15) 4 (17) 23 (19) .95
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Note: Data are frequencies (percentages); words are alphabetized; neuropathic words are above the dotted line; nociceptive words are below the dotted line (Wilkie et al., 2001).

*

Fisher’s exact test.

We tested eight sets of sensory pain quality descriptors based on subclasses described by Melzack (1975) and classified as neuropathic (Wilkie et al., 2001). We tested one set of MPQ sensory pain quality descriptors that appear on at least one other valid neuropathic pain screening tool. The comparisons of the nine sets of pain quality descriptors by the QST-derived classifications appear in Table 3. The set of sensory pain quality descriptors with the highest mean score value was “sensory,” which included the sensory pain quality descriptors cold, cool, and freezing. The central sensitization group mean for the sensory set was M = 10.6, SD = 4.0 (Table 3). The set of sensory pain quality descriptors with the lowest mean score value was for the set “temporal.” The central sensitization group mean for the temporal set was M = 0.1, SD = 0.2 (Table 3). Out of the nine sets of pain quality descriptors, no statistically significant difference was found between classification groups,

Table 3.

Scores, Means and Standard Deviation for Sets of Neuropathic Pain Quality Descriptors and QST Classification

Sets of Words Overall (n = 179)
 Central (n = 33)
 Mixed (n = 23)
 Normal (n = 123)
 F p-Value*
M SD M SD M SD M SD
Brightness1 1.4 1.9 1.9 2.0 1.6 2.0 1.2 1.8 2.08 .13
Pressure2 1.6 1.5 1.9 1.5 1.7 1.5 1.5 1.5 .831 .44
Sensory3 9.0 5.2 10.6 4.0 9.9 4.7 8.4 5.5 2.69 .07
Sensory Misc.4 .8 .9 .9 .9 1.1 1.2 .7 .9 2.45 .09
Sensory Misc2.5 .6 .7 .7 .8 .4 .7 .5 .7 1.28 .28
Spatial6 .6 .5 .5 .5 .7 .4 .5 .5 1.94 .15
Temporal7 .1 .3 .1 .2 .1 .2 .1 .3 1.20 .40
Thermal8 2.9 4.2 3.8 4.5 3.5 4.5 2.5 4.0 1.63 .21
NP Tools9 1.0 1.1 1.2 1.1 1.1 1.1 .9 1.0 1.20 .31
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Note: M = mean; SD = standard deviation.

1

tingling, itchy, smarting, stinging

2

pricking, boring, drilling, stabbing, lancinating

3

cool, cold, freezing

4

spreading, radiating, penetrating

5

tight, numb, drawing

6

jumping, flashing, shooting

7

flickering, quivering

8

hot, burning, scalding, searing

9

NP Tools = neuropathic pain tools; jumping, stabbing, burning, tingling

*

Analysis of variance (ANOVA), p < .05

Discussion

Our study is the first to examine the association between MPQ sensory pain quality descriptors and QST-derived classifications in adults with SCD. In our exploratory study, we examined the 54 MPQ sensory pain quality descriptors and nine sets of descriptors selected by adults with SCD and compared the descriptors or sets of descriptors across the QST-determined classifications. Although every MPQ descriptor was selected by at least one participant, only five descriptors were selected by different proportions of the QST-classification groups. These five descriptors were selected by larger proportions of participants found to have some sensitization (central and/or mixed sensitization) compared to participants classified as normal sensation. Three of the five descriptors selected by larger proportions of participants classified as sensitized are associated with neuropathic pain in the research literature. For unknown reasons, contrary to our expectations, the other sets—the other 25 descriptors of neuropathic pain—and the other 24 descriptors of nociceptive pain did not discriminate significantly between the normal sensation and mixed and central sensitization groups. This is possibly related to the presence of multiple pain types resulting from the lifetime of pain experienced by many adults with SCD.

As pain of SCD usually begins in infanthood and continues into adulthood, pain pathways may be activated over extended periods of time and result in both acute, episodic and chronic, intractable pain. Chronic pain in adults with SCD may result from peripheral and central sensitization, but interestingly, only one participant in our sample had evidence of peripheral sensitization alone, which was not a large enough group to include in other analyses. Central sensitization occurs when continued pain signals from nociceptive receptors in the periphery alter the processing in the spinal cord or brain resulting in heightened pain sensations such as allodynia and hyperalgesia (Woolf, 2011). Recent research in adults with SCD indicated the presence of allodynia and hyperalgesia leading to the conclusion that a component of the pain experienced by adults with SCD may arise from neuropathic mechanisms (Campbell, Carroll et al., 2016; Ezenwa et al., 2016). As with our study, in other research with pain quality descriptors adults with SCD selected pain quality descriptors that are consistent with neuropathic pain (Wilkie et al., 2010), but in that study no sensory findings were available for validation in SCD.

An important finding is that adults with SCD classified as sensitized by QST selected sensory pain descriptors that, based on extensive literature were useful for the diagnosis of neuropathic pain in SCD and other pain conditions (Melzack, 2005; Melzack, 1975; Wilkie et al., 2001). For example, aching is found in the literature to characterize both neuropathic (Dubuisson & Melzack, 1976; Masson et al., 1989; Wilkie et al., 2001) and nociceptive (Dubuisson & Melzack, 1976) pain conditions. Aching and cold are consistent with descriptors selected in neuropathic pain conditions including diabetic peripheral neuropathy, postherpetic neuralgia, spinal cord injury, and cerebral palsy (Dudgeon et al., 2005; Mackey et al., 2012). However, in our study, aching was selected by a smaller proportion of adults with SCD classified by QST as having central sensitization, and cold was selected by a larger proportion of those classified by QST as sensitized (central and mixed). Research with pain quality descriptors and 145 patients with SCD found that participants with SCD selected descriptors aching (68%), cold (16%), and spreading (25%) (Wilkie et al., 2010). Beating and throbbing are found in the literature to characterize nociceptive pain; however, in our study beating and throbbing were both selected by a larger proportion of adults with SCD that were classified by QST as sensitized, either central or mixed sensitization (Boureau et al., 1990; Wilkie et al., 2001).

Measurement of pain is of concern for clinicians and researchers in part because pain is a subjective experience, and there may be large differences in sensitivity even among individuals suffering from the same pain condition. Our findings of a relationship between some sensory pain quality descriptors and sensitization in adults with SCD can be applied to the education of clinicians and patients. Understanding the language utilized by those experiencing pain can direct researchers and clinician decision-making, and open dialogue between clinician and patient and help to create a more satisfying experience with the healthcare system for adults with SCD.

One potential limitation of our study is the small percentage of participants classified by QST with peripheral sensitization. Although our small percentage with peripheral pain is similar to the findings in a pilot study (Ezenwa et al., 2016), our findings may not be characteristic of all African-American adults with SCD. It will be important in future research to validate the prevalence of peripheral sensitization in adults with SCD. Adults with SCD suffer a lifetime of pain that may result in the presence of multiple pain types. As part of PAINReportIt®, patients completed a body outline to illustrate all of their pain sites. Based on the QST protocol, we tested only two of these pain sites. Future studies should explore which sensory pain quality descriptors are associated with specific pain sites—especially those likely to be indicative of neuropathic pain. Another issue that may be viewed as a limitation is the issue of multiplicity. As our study was an exploratory analysis to generate hypotheses to be tested through future study, we did not perform adjustments for the multiple tests (Feise, 2002).

The complex relationship between sensory pain quality descriptors and QST-derived classification presents interpretive problems in establishing associations without considering the influence of other variables (e.g., current pain, pain intensity over time, pain location). Our findings show some association with sensory pain quality descriptors and central sensitization; future studies should include nerve conduction testing and sensory pain quality descriptors. Our study was an exploratory analysis to generate hypotheses about sensory pain quality descriptors and QST-derived normal or sensitized classifications with the expectation that hypotheses could be tested through future study. Control of variables, such as clinical pain ratings or age differences, was not the intention of this work; additional studies are needed to determine other variables that discriminate classification groups rather than controlling for the variables. The inclusion of pain intensity with sensory pain quality descriptors could be considered for the next phase of research in sensory pain quality descriptors and QST-derived classification.

Conclusion

Our finding that five sensory pain quality descriptors were statistically significant across the QST classifications offers potential value for the MPQ to differentiate pain mechanisms in adults with SCD. Because all clinics do not have access to QST measures required for classification, the development of standardized assessment tools with discriminatory properties—that are efficient and do not lengthen the clinic visit—could provide a valuable self-report pain assessment tool that aids researchers and clinicians in pain management and treatment decision-making.

Acknowledgement

The study was supported by grant number R01HL124945 from the National Institutes of Health, National Heart Lung & Blood Institute (NHLBI). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH, NHLBI. The final peer-reviewed manuscript is subject to the National Institutes of Health Public Access Policy.

Conflict of Interest:

Drs. Dyal and Fillingim have nothing to disclose. Drs. Ezenwa, Yao, Yoon, Schlaeger, Suarez, and Molokie report grants from NHLBI, during the conduct of the study. Dr. Wang reports grants from NIH, during the conduct of the study. Dr. Wilkie reports grants from NHLBI, during the conduct of the study; and other from eNursing llc, outside the submitted work.

Ethical Conduct of Research: The original study was approved by the University of Illinois Chicago (UIC) institutional review board (IRB), and written signed consent of the participants was obtained. Approval to conduct the analysis of existing data was obtained from the University of Florida prior to request for the de-identified dataset.

Contributor Information

Brenda W. Dyal, University of Florida College of Nursing, Gainesville, FL.

Miriam O. Ezenwa, University of Florida College of Nursing, Gainesville, FL.

Saun-Joo Yoon, University of Florida College of Nursing, Gainesville, FL.

Roger B. Fillingim, University of Florida College of Dentistry, Gainesville, FL.

Yingwei Yao, University of Florida College of Nursing, Gainesville, FL.

Judith M. Schlaeger, University of Illinois at Chicago College of Nursing Chicago, IL.

Marie L. Suarez, University of Illinois at Chicago College of Nursing Chicago, IL.

Zaijie J. Wang, University of Illinois at Chicago College of Pharmacy, Chicago, IL.

Robert E. Molokie, University of Illinois at Chicago College of Medicine, Jesse Brown VA Medical Center, Chicago, IL.

Diana J. Wilkie, Director, Center for Palliative Care Research and Education, University of Florida College of Nursing, Gainesville, FL.

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