Differential Sensory and Clinical Phenotypes of Patients With Chronic Widespread and Regional Musculoskeletal Pain

Marina M. Finnern; Dieter Kleinböhl; Herta Flor; Justus Benrath; Rupert Hölzl

Pain. 2020;162(1):56-70.

Limitations

This cross-sectional study has several limitations: We included nonrandom clinic attendant samples that may not be representative of the chronic pain population in general. Moreover, we used multiple sequential structure-finding methods in which the indicator sets for the final phenotyping were optimized to retain maximum case numbers. The statistical probabilities of this explorative definition phase are inflated, but the final profile clustering is not, nor are the comparisons between clusters with respect to diagnoses, comorbidity, or psychosocial factors, which were corrected for α-inflation. The combined explorative-inferential strategy may also have lost relevant phenotypes marked by indicators that were abandoned because of sample attrition, sex prevalence differences, or unreliability of sensory assessments. The positively identified phenotypes, however, should be valid and so should the core result on the phenotypical heterogeneity of fibromyalgia and regional pain categories and the necessity to reinstall sufficient sensory assessment.

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Acknowledgements
This study was supported by grants of the Deutsche Forschungsgemeinschaft (Clinical Research Group 107, project 03 to H.F. and project 04 to R.H.; Collaborative Research Center 1158, project B03 to H.F.). M.M. Finnern was supported by a PhD scholarship of the Friedrich-Ebert-Stiftung e.V. The authors are indebted to the colleagues of the collaborating pain clinics who created the extensive sensory and clinical database used in this work.
Previous presentation: The study is based in part on the doctoral thesis of M.F.¹³ Part of the results (spatial clusters of pressure sensitivity) has been presented as poster at the World Congress of the International Association for the Study of Pain 2018, Boston, MA.

Table 1. Sociodemographics, pain characteristics, and comorbid medical diagnoses.
	Pain diagnosis
	FMS: N = 78†	CBP: N = 107‡
Age (y)
Mean ± SD	50.8 ± 9.5	48.3 ± 12.2
Range	23–68	18–68
Sex
Female	73 (93.6)	69 (64.5)
Male	5 (6.4)	38 (35.5)
Education
Up to college level	62 (79.5)	77 (72.0)
University	11 (14.1)	19 (17.8)
Missing	5 (6.4)	11 (10.3)
Work
Working	26 (33.3)	46 (43.0)
Not working	47 (60.3)	51 (47.7)
Missing	5 (6.4)	10 (9.3)
Pain characteristics
Present pain intensity§	3.3 ± 1.3	3.0 ± 1.3
Pain severity§	3.7 ± 1.1	3.4 ± 1.1
Pain duration (mo)§	50 ± 25	48 ± 32
CPG§	3 ± 1	2 ± 1*
Widespread pain†
4 quadrants + axis	71 (91.0)	28 (26.2)**
<5 regions	2 (2.6)	69 (64.5)**
FS scale\|\|
FMS criterion ≥12	63 (80.8)	23 (21.5)
FMS criterion <12	15 (19.2)	84 (78.5)
Mean ± SD	16.3 ± 6.3	8.2 ± 4.5**
Median ± 0.5 IQD	17.0 ± 4.5	8.0 ± 3.0**
Range	0–20	0–20
WPI\|\|
Mean ± SD	11.8 ± 3.8	5.5 ± 2.9**
Median ± 0.5 IQD	12 ± 3.0	5 ± 1.5**
Range	4–19	0–15
No. of present pain sites¶
Mean ± SD	6.8 ± 1.4	4.7 ± 1.7**
Median ± 1/2 IQD	7 ± 1	4.5 ± 1**
Range	3–9	0–9
Pain all over my body#	15 (19.2)	1 (0.9)
Comorbid diagnoses††
Neoplastic	3 (3.8)	8 (7.5)
Neurological	2 (2.6)	4 (3.7)
Otorhinal-respiratory	31 (39.7)	18 (16.8)
Cardiovascular	13 (16.7)	6 (5.6)
Gastrointest.-liver-pancreas	17 (21.8)	13 (12.1)
Endocrinol.-metabolic	10 (12.8)	7 (6.5)
Urogenital, kidney	10 (12.8)	12 (11.2)
Allergies, intolerances	38 (48.7)	27 (25.2)
No diagnose	22 (28.2)	50 (46.7)
Missing	5 (6.4)	9 (8.4)

Differences: t test, U test, C_corr, and K-S 2-sample test; *P < 0.05, **P < 0.001, Bonferroni–Holm corrected.
†ACR criteria 1990: 11 of 18 TPs; "widespread pain": present pain in 4 body quadrants plus axis.⁷⁴
‡Chronic primary back pain: pain ≥6 months in the upper or lower back, primary pain not related to acute trauma, inflammatory or neurologic disease, radicular and neuropathic signs absent; cf. "chronic primary pain."^49,67
§Present intensity of the major pain (MPI-D, item #1) and global pain severity score (MPI-D Scale 1, section I) summarizing present and recent pain with perceived suffering (t test: P = 0.033, n. s. after correction)¹⁷; duration: Deutscher Schmerzfragebogen (DSF), item #25: time since onset⁴⁸; CPG (U test: P = 0.007).⁴³
||FS scale⁷¹; WPI: 0–19 according to the FSQ.²⁸
¶Present pain sites reported by patients corresponding to Axis I, IASP Taxonomy of chronic pain³⁴; responses to item #20 in DSF.⁴⁸
#Response "pain all over my body" to item #21⁴⁸; N cases (%).
††Self-reported medical life-time diagnoses of specialist disciplines; responses to item #40 in DSF⁴⁸; N cases (%); multiple mentions allowed; diagnosed musculoskeletal disorders not listed.
CBP, chronic primary back pain; CPG, Chronic Pain Grade; DSF, Deutscher Schmerzfragebogen (German Pain Questionnaire); FMS, fibromyalgia syndrome; FS scale, Fibromyalgia Symptom scale; FSQ, Fibromyalgia Survey Questionnaire; IQD, interquartile distance; MPI, Multidimensional Pain Inventory; TP, tender point; WPI, Widespread Pain Index.

Table 2. Spatial distribution of pressure sensitivity in the standardized manual test.
Variable	FMS: 78	CBP: 107
No. of sensitive tender points†
Mean ± SD	15.0 ± 2.8	5.0 ± 4.6**
Median ± 1/2 IQD	15.5 ± 3.0	4.0 ± 4.0**
Range	7.0–18.0	0.0–18.0
Valid cases	76	102
No. of sensitive CPs†
Mean ± SD	4.4 ± 4.0	1.1 ± 2.0**
Median ± 1/2 IQD	3.0 ± 3.3	0.0 ± 1.0**
Range	0.0–14.0	0.0–10.0
Valid cases	77	101
Total no. of sensitive points†
Mean ± SD	19.2 ± 6.1	6.1 ± 6.6**
Median ± 1/2 IQD	19.0 ± 4.8	4.0 ± 4.3**
Range	0.0–32.0	0.0–26.0
Valid cases	77	102
Pain intensity tender points‡
Mean ± SD	5.8 ± 1.7	4.2 ± 1.8**
Median ± 1/2 IQD	5.7 ± 1.3	4.0 ± 1.2**
Range	2.6–10.0	1.0–10.0
Valid cases	N = 76	N = 102
Pain intensity CPs‡
Mean ± SD	4.9 ± 1.9	3.8 ± 1.9 *
Median ± 1/2 IQD	4.8 ± 1.3	3.0 ± 1.1 *
Range	1.5–9.0	1.0–10.0
Valid cases	62	33
Pain intensity all points‡
Mean ± SD	5.5 ± 1.6	4.10 ± 1.7**
Median ± 1/2 IQD	5.6 ± 1.2	3.7 ± 1.2**
Range	2.7–9.6	1.0–10.0
Valid cases	76	81
Pain intensity head-cervical region§
Mean ± SD	5.1 ± 1.9	4.1 ± 1.8*
Median ± 1/2 IQD	5.0 ± 1.5	4.0 ± 1.4*
Range	1.8–9.4	1.0–10.0
Valid cases	74	54
Pain intensity thoracic region§
Mean ± SD	5.6 ± 1.8	4.1 ± 1.8**
Median ± 1/2 IQD	5.6 ± 1.4	4.0 ± 1.4**
Range	1.3–10.0	1.0–8.1
Valid cases	76	63
Pain intensity lumbar region§	N = 76	N = 38
Mean ± SD	5.8 ± 2.3	4.1 ± 1.8**
Median ± 1/2 IQD	5.9 ± 2.0	4.0 ± 1.0**
Range	1.0–10.0	1.0–10.0
Pain intensity upper limbs§
Mean ± SD	5.5 ± 2.0	4.1 ± 2.1**
Median ± 1/2 IQD	5.5 ± 1.5	4.0 ± 1.3**
Range	1.9–10.0	1.0–10.0
Valid cases	68	34
Pain intensity lower limbs§
Mean ± SD	5.6 ± 1.9	4.0 ± 2.3**
Median ± 1/2 IQD	5.8 ± 1.6	3.3 ± 2.0**
Range	2.0–9.5	1.0–8.5
Valid cases	74	45

Differences: *P < 0.01, **P < 0001; U tests, familywise Bonferroni–Holm corrected with k = 3 for number of sites and related intensities and k = 5 for regional intensities.
†Number of TPs and CPs on both body sides with VAS ratings ≥1, corrected for individual number of test sites. Differences between left and right body sides n. s. (t test, Wilcoxon).
‡Average pressure pain intensity ratings (VAS 0–10) of the manual probes in 18 tender, 14 control, and all 32 points tested.
§Average pressure pain intensity ratings (VAS 0–10) of the manual probes in the 5 body regions of the Heidelberg pain drawing mask (zero values excluded).²³
CBP, chronic primary back pain; CP, control point; FMS, fibromyalgia syndrome; IQD, interquartile distance; TP, tender point; VAS, visual analogue scale.

Table 3. Spatial distribution of pressure sensitivity in the algometer test at the trapezius tender point and thenar control point.
	FMS: 78	CBP: 107	PFC: 41§
Pain threshold trapezius†
Mean ± SD	24.03 ± 14.32	40.99 ± 16.77*	34.81 ± 9.51*
Median ± 1/2 IQD	20.10 ± 13.04	39.23 ± 8.14	34.32 ± 4.61
Range	0.98–68.65	7.36–97.09	15.20–71.10
Valid cases	78	74	40
Pain threshold thenar†
Mean ± SD	27.95 ± 12.36	36.38 ± 9.71*	32.36 ± 9.81
Median ± 1/2 IQD	32.36 ± 10.79	39.23 ± 3.92	32.85 ± 7.75
Range	0.98–49.03	9.32–66.20	12.75–53.94
Valid cases	78	70	40
Pain intensity trapezius‡
Mean ± SD	5.99 ± 2.12	3.92 ± 2.81*	4.26 ± 2.83*
Median ± 1/2 IQD	6.00 ± 1.75	4.00 ± 2.63	5.00 ± 2.50
Range	1.00–10.00	0.00–9.00	0.00–8.00
Valid cases	77	101	38
Pain intensity thenar‡
Mean ± SD	3.14 ± 3.00	2.84 ± 2.93	4.26 ± 2.74
Median ± 1/2 IQD	3.00 ± 2.75	2.50 ± 2.75	4.00 ± 2.5
Range	0.00–9.00	0.00–9.00	0.00–8.00
Valid cases	77	102	39

†Phasic pressure pain thresholds ("just painful"), ascending method of limits, 4.9 N/s ramps; average of 3 trials with 1 initial accommodation trial. No significant differences between left and right body sides (t test, Wilcoxon).
‡Mean pain intensity ratings (NRS 0–10) for complete stimulation series for pain threshold testing. No significant differences between left and right body sides (t test, Wilcoxon).
§Differences: *P < 0001; t tests of FMS or CBP (2 groups × 4 variables) against PFC; familywise Bonferroni–Holm corrected with k = 2 for 2 thresholds and 2 intensities.
CBP, chronic primary back pain; FMS, fibromyalgia syndrome; IQD, interquartile distance; NRS, numerical rating scale; PFC, pain-free controls.

Table 4. Sensory-clinical phenotypes in patients with FMS and CBP: FMS and CBP diagnoses across phenotype clusters.
Diagnosis†	Cluster*				Σ
Diagnosis†	1	2	3	4	Σ
FMS	44‡ [94/64]	16 [76/23]	9 [16/13]	0 [0/0]	69
CBP	3 [6/3]	5 [24/6]	49 [84/54]	33 [100/37]	90
FS ≥12	40 [85/49]	17 [81/21]	19 [33/23]	5 [15/6]	81
FS <12	7 [15/9]	4 [19/5]	39 [67/50]	28 [85/39]	78
Σ	47	21	58	33	159

*Cluster numbering according to CBP = non-FMS frequency; LCA maximum likelihood extraction sequence 4-1-3-2.
‡Absolute frequencies, column/row % in brackets.
†Correlation clusters × previous diagnoses: C_corr = 0.881, P < 0.001; clusters × FS ≥12: C_corr = 0.713, P < 0.001.
CBP, chronic primary back pain; FMS, fibromyalgia syndrome; FS, Fibromyalgia Symptom scale; LCA, latent class analysis.

Table 5. Sensory-clinical phenotypes in patients with FMS and CBP: discriminator profiles of phenotype clusters.
Indicator	Cluster				Distance*
Indicator	1	2	3	4	Distance*
1. Sensitive TPs^†	16 ± 1.5	13 ± 3.0	6.5 ± 3	0 + 2	302.78
2. Pressure pain intensity^‡	6.0 ± 2.0	6.0 ± 1.5	2.0 ± 2.0	0.0 ± 0.0	220.00
3. WPI^†	13 ± 3.0	11 ± 3.0	5 ± 1.6	4 ± 2.0	168.41
4. Sensitive CPs^†	3 ± 2.5	6 ± 2.3	0 + 2	0 ± 0‡	150.01
5. Pressure pain threshold^§	16.6 ± 7.9	39.1 ± 1.3	44.8 ± 20.9	35.1 ± 8.5	67.35
6. Present pain intensity^\|\|	3.0 ± 0.5	4.0 ± 0.5	3.00 ± 1	3.0 ± 1	50.01
Cluster description	Wide-spread pain; high sensitivity	Mixed pain; moderate sensitivity	Mixed pain; normal sensitivity	Regional pain; low sensitivity

*Absolute cluster mean differences of all cluster pairs for the indicator (0–100, modified after⁶⁵). The nonparametric estimator does not regard oblique relations and provides only ordinal ranking of the LCA discriminators for parameter selection (standardized point distances per indicator in supplementary Table S11, available at https://links.lww.com/PAIN/B131).
†Absolute frequencies: 18 ACR TPs, 14 CPs, and 19 WPI body sites; medians ± 0.5 IQD.
‡Pressure pain intensity of the manual test at the right trapezius, VAS rating from no to worst pain, transformed to values 0–10; medians ± 0.5 IQD.
§Pressure pain threshold algometer test; Newton; mean ± SD.
||Present pain intensity (MPI, item #1), NRS scale 0–6; medians ± IQD.
CP, control point; IQD, interquartile distance; LCA, latent class analysis; MPI, Multidimensional Pain Inventory; NRS, numerical rating scale; TP, tender point; VAS, visual analogue scale; WPI, Widespread Pain Index.

Table 6. Pain, comorbidity, and psychosocial factors of 4 sensory-clinical phenotypes of patients with previous FMS and CBP diagnoses.
Variable†	Cluster				Difference‡ between clusters 1 and 2 and clusters 3 and 4
Variable†	1 (N = 47)	2 (N = 21)	3 (N = 58)	4 (N = 33)	Difference‡ between clusters 1 and 2 and clusters 3 and 4
Age (y)	49.9 ± 8.9 [22–63]	48.4 ± 12.9 [23–69]	50.2 ± 11.3 [23–68]	47.5 ± 13.7 [18–67]	n. s.
Sex (f/m)	45/2	19/2	39/19	20/13	χ²(1,4); P < 0.001***
Chronicity^§
Duration (mo)	50 ± 27 [60 ± 18]	50 ± 28 [60 ± 9]	48 ± 27 [60 ± 18]	48 ± 34 [60 ± 18]	n. s.
CPG	3.1 ± 1.2 [3.5 ± 1.0]	2.8 ± 1.1 [3.0 ± 1.0]	2.2 ± 1.2 [2.0 ± 1.0]	2.2 ± 1.4 [1.0 ± 1.5]	P < 0.001***d = 0.650
Pain characteristics^\|\|
WPI	12.1 ± 3.7 [13.0 ± 3.0]	11.2 ± 4.1 [11.0 ± 3.0]	6.2 ± 3.0 [5.0 ± 1.6]	5.0 ± 3.2 [4.0 ± 2.0]	P < 0.001***d = 1.773
Intensity	3.3 ± 1.24 [3.0 ± 0.5]	3.4 ± 1.3 [4.0 ± 0.5]	2.9 ± 1.17 [3.0 ± 1.0]	3.1 ± 1.46 [3.0 ± 1.0]	P = 0.012*d = 0.395
Severity	3.8 ± 1.1 [3.7 ± 0.9]	3.9 ± 1.1 [4.0 ± 1.2]	3.2 ± 1.1 [3.0 ± 0.9]	3.6 ± 1.1 [3.5 ± 0.7]	P = 0.005*d = 0.462
Pain impact¶
FM impact	56.6 ± 18.6 [55.8 ± 13.4]	53.7 ± 14.3 [56.3 ± 12.7]	42.9 ± 14.8 [42.4 ± 12.9]	39.9 ± 19.8 [34.4 ± 14.9]	P < 0.001***d = 0.797
Interference	3.5 ± 1.4 [3.8 ± 1.2]	3.3 ± 1.4 [3.6 ± 0.9]	2.4 ± 1.2 [2.5 ± 0.9]	3.4 ± 1.4 [3.6 ± 1.2]	P = 0.008*d = 0.504
Functional capacity	54.5 ± 16.9 [54.2 ± 13.4]	57.5 ± 15.2 [58.3 ± 11.5]	74.6 ± 17.3 [75.0 ± 10.4]	68.3 ± 20.0 [70.8 ± 13.5]	P < 0.001***d = 0.967
Pain cognitions#
Catastrophizing	2.6 ± 1.1 [2.6 ± 0.9]	2.3 ± 0.6 [2.3 ± 0.3]	1.8 ± 0.9 [1.9 ± 0.8]	1.7 ± 1.1 [1.6 ± 0.6]	P < 0.001**d = 0.826
Return to work	12.9 ± 9.8 [12.0 ± 9.5]	9.6 ± 8.8 [7.0 +7.5]	6.9 + 9.1 [5.0 ± 4.5]	9.9 ± 8.0 [11.5 ± 8.4]	P = 0.061
Somatic symptoms††
GBB sum	46.9 ± 16.8 [50.0 ± 12.0]	38.0 ± 10.3 [38.0 ± 6.0]	30.1 ± 14 [26.0 ± 10.5]	24.6 ± 15.5 [19.0 ± 9.8]	P < 0.001***d = 1.273
GBB exhaustion	14.6 ± 5.8 [15.0 ± 4.8]	12.2 ± 4.6 [12.0 ± 4.8]	9.5 ± 5.8 [9.0 ± 4.0]	7.8 ± 6.6 [6.0 ± 4.3]	P < 0.001***d = 0.849
GBB gastrointest.	7.6 ± 5.6 [7.0 ± 4.1]	5.0 ± 3.0 [5.0 ± 2.5]	4.1 ± 3.4 [3.0 ± 2.5]	3.3 ± 4.0 [2.0 ± 3.0]	P < 0.001***d = 0.674
GBB cardiovascul.	7.0 ± 4.3 [6.5 ± 3.1]	5.4 ± 3.5 [5.0 ± 3.0]	3.9 ± 3.6 [3.0 ± 2.5]	2.7 ± 3.6 [2.0 ± 2.0]	P < 0.001***d = 0.794
GBB musc.-skeletal	17.3 ± 4.5 [17.0 ± 3.1]	15.2 ± 4.1 [16.0 ± 2.3]	12.6 ± 4.4 [12.0 ± 3.0]	10.8 ± 4.2 [11.0 ± 3.8]	P < 0.001***d = 1.072
SF-12 physical	29.6 ± 7.2 [29.1 ± 5.2]	35.2 ± 9.9 [32.4 ± 5.7]	38.4 ± 9.0 [38.8 ± 7.0]	35.6 ± 9.2 [38.1 ± 8.1]	P < 0.001***d = 0.690
PSQI sleep	10.3 ± 4.3 [11.0 ± 2.8]	11.7 ± 3.8 [12.0 ± 2.4]	9.0 ± 4.4 [8.0 ± 3.2]	7.9 ± 4.8 [8.0 ± 3.5]	P = 0.028
FGID [N (%)]	18 (38.3)	9 (42.9)	12 (20.7)	1 (3.0)	P = 0.006*d = 0.390
Comorbidity with mental disorder‡‡
Anxiety	48.3 ± 12.5 [47.0 ± 10.5]	50.7 ± 10.8 [51.5 ± 9.4]	43.7 ± 9.5 [41.0 ± 7.5]	42.2 ± 11.2 [39.0 ± 6.8]	P = 0.012
Depression	22.3 ± 12.3 [21.0 ± 9.0]	20.3 ± 12.3 [20.0 ± 5.0]	19.6 ± 9.8 [17.5 ± 6.1]	19.6 ± 13.0 [16.0 ± 7.5]	P = 0.262
Psychosoc. factors§§
Stress perception	34.2 ± 15.8 [34.0 ± 12.8]	36.7 ± 13.5 [35.0 ± 12.0]	30.8 ± 12.9 [28.5 ± 11.4]	25.7 ± 10.7 [25.5 ± 8.6]	P = 0.067
Social support	3.6 ± 1.7 [3.8 ± 1.3]	3.3 ± 1.8 [4.0 ± 1.5]	2.8 ± 1.7 [3.0 ± 1.4]	3.2 ± 1.7 [3.5 ± 1.1]	P = 0.076
Solicitous response	3.2 ± 1.6 [3.2 ± 1.5]	3.0 ± 1.6 [3.4 ± 1.4]	2.5 ± 1.4 [2.6 ± 1.2]	2.7 ± 1.5 [2.8 ± 1.2]	P = 0.030

†Mean ± SD, medians ± 0.5 interquartile distances in brackets; frequencies and range for categorical variables.
‡Exact probabilities of the ex-post t test (or U test if required); effect sizes according to scale levels: Cohen's d (interval), z values transformed to η² (ordinal) or phi coefficient (nominal) of the cluster-pair difference between clusters 1 and 2 and clusters 3 and 4 after a significant H-test or contingency test. Significance levels Bonferroni–Holm corrected, familywise for the independent domains pain characteristics and chronicity (k = 7), pain impact (k = 4), pain cognitions and coping (k = 7), comorbidity (k = 12), psychosocial factors, and stress (k = 13). *P < 0.05; **P < 0.01; ***P < 0.001 after correction; variables with differences P > 0.10 not shown but included in correction.
§CPG,⁴³ Md ± 0.5 IQD, and frequencies of individual grades, expected frequencies in parentheses.
||WPI: range 0–19 according to the FSQ,²⁸ the survey version of the FS scale.⁷¹ Intensity: item #1 of the MPI-D;¹⁷ Severity: MPI-D = scale value.
¶FM Impact: Fibromyalgia Impact Questionnaire (German version⁵¹; original version⁸); Interference: MPI-D scale; Functionality: FFbH-R.⁴²
#Catastrophizing: PRSS;¹⁶ Belief return to work: FABQ.⁵³
††GBB sum: total somatic load, sum score of the Giessen Subjective Complaints List (GBB-24);⁶ GBB subscales: exhaustion; gastrointestinal, musculoskeletal complaints; SF-12 physical: somatic component of the Health-Related Quality of Life Questionnaire—Short Version (SF-12)⁷; PSQI sleep: sum score of the Pittsburgh Sleeping Quality Index;⁹ FGID [N (%)]: absolute/relative frequency of functional g. i. t. disorders according to the self-report questionnaire for functional gastrointestinal disorders (functional dyspepsia/nonulcer dyspepsia and/or irritable bowel syndrome).³¹
‡‡STAI-T⁴⁴ Center for Epidemiological Studies Depression Scale—German Version (ADS).³⁰
§§Stress load: subjective global strain load according to the BSS (German "Kurzer Fragebogen zur Erfassung von Belastungen")¹⁵; Social support: MPI-D¹⁷; Solicitous resp.: MPI-D scale solicitous response of spouse.
BSS, Brief Stress Scale; CBP, chronic primary back pain; CPG, Chronic Pain Grade; FAPQ, Fear-Avoidance-Beliefs Questionnaire; FFbH, Hannover Functional Ability Questionnaire; FGID, functional gastrointestinal disorders; FMS, fibromyalgia syndrome; FS scale, Fibromyalgia Symptom scale; FSQ, Fibromyalgia Survey Questionnaire; IQD, interquartile distance; MPI, Multidimensional Pain Inventory; PRSS, Pain-Related Self-Statements Scale; PSQI, Pittsburgh Sleep Quality Index; STAI-T, Trait Anxiety Scale of the State-Trait Anxiety Inventory; WPI, Widespread Pain Index.