Heterogeneity Within the Fibromyalgia Population: Theoretical Implications of Variable Tender Point Severity Ratings

HILARY D. WILSON; TERENCE W. STARZ; JAMES P. ROBINSON; DENNIS C. TURK

doi:10.3899/jrheum.090432

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Figure 1.
Mean scores on the NS (neck/shoulder), GT (gluteal/trochanteric), UE (upper extremity), CON (control) factors for the 3 groups in the cluster solution. The HH (high/high) group was at least 25% higher than all other clusters on all standard TP sets (NS = 7.53 ± 1.25, GT = 8.12 ± 1.44, and UE = 7.59 ± 1.70), and over 2.5 times higher on the control domain (3.76 ± 1.91). Scores on the standard TP sets for the ML (moderate/low) cluster (NS = 5.3 ± 1.39, GT = 6.29 ± 1.83, UE = 6.02 ± 1.50) were all within one-half SD of the mean for all groups, and lower than one-half SD on the control factor (CON = 1.12 ± 1.16). Scores on the LL (low/low) group were more than one-half SD lower than the mean for both the standard and control factors (NS = 4.27 ± 1.74, GT = 4.19 ± 2.19, UE = 2.34 ± 1.55, CON = 1.15 ± 1.28).

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Table 1.

Demographic characteristics of patients with fibromyalgia (FM) for Sample 1 (n = 690) and Sample 2 (n = 743). Values are expressed as mean (SD) unless otherwise indicated.

Variable	Sample 1 (n = 690)	Sample 2 (n = 743)	Total (n = 1433)	p
Average age, yrs	48.95 (11.55)	49.80 (10.95)	49.39 (11.24)	0.15
Female, n (%)	664 (94.7)	718 (94.5)	1382 (94.6)	0.83
Duration of FM, mo	115.77 (97.01)	115.85 (94.42)	95.64 (2.51)	0.99
Height, m	1.64 (0.08)	1.64 (0.08)	1.64 (0.08)	0.71
BMI, weight/height, m²	30.57 (7.20)	30.92 (7.42)	30.75 (7.31)	0.35

BMI: body mass index.

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Table 2.

Frequency and average tender point severity for individual tender points and factor scores for total sample (n = 1433).

Tender Point (right)	Frequency	Mean (SD)
Occiput	1323 (90.3)	4.86 (2.78)
Trapezius	1410 (96.2)	6.13 (2.54)
Supraspinatus	1374 (93.8)	5.71 (2.75)
Low cervical	1389 (94.8)	5.85 (2.67)
Second rib	1400 (95.6)	6.01 (2.60)
N/S factor mean		5.68 (1.98)
Greater trochanter	1385 (94.5)	6.48 (2.83)
Gluteal	1353 (92.4)	6.31 (2.76)
G/T factor mean		6.58 (2.31)
Lateral epicondyle	1363 (93.0)	5.67 (2.78)
UE factor mean		5.61 (2.63)
Thumbnail	541 (36.9)	1.41 (2.34)
Mid-forehead	613 (41.8)	1.51 (2.27)
Dorsum forearm	950 (64.8)	2.95 (2.97)
CON factor mean		1.96 (1.98)
Knee (not in solution)	1384 (94.5)	6.18 (2.82)

N/S: neck/shoulder; G/T: gluteal/trochanteric; UE: upper extremity; CON: control.

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Table 3.

Factor loadings and communalities (h²; loadings below 0.45 are replaced by 0).

Item	NS	GT	UE	CON	h²
Occiput (R)/(L)	0.69/0.69	0/0	0/0	0/0	0.59/0.58
Trapezius (R)/(L)	0.77/0.79	0/0	0/0	0/0	0.63/0.64
Supraspinatus (R)/(L)	0.69/0.69	0/0	0/0	0/0	0.60/0.59
Low cervical (R)/(L)	0.68/0.65	0/0	0/0	0/0	0.59/0.59
Second rib (R)/(L)	0.61/0.59	0/0	0/0	0/0	0.59/0.59
Greater trochanter (R)/(L)	0/0	0.81/0.80	0/0	0/0	0.69/0.68
Gluteal (R)/(L)	0/0	0.72/0.72	0/0	0/0	0.62/0.65
Lateral epicondyle (R)/(L)	0/0	0/0	0.69/0.69	0/0	0.65/0.66
Thumbnail (L)	0/0	0/0	0/0	0.84	0.67
Mid-forehead	0/0	0/0	0/0	0.72	0.59
Dorsum forearm (R)	0/0	0/0	0/0	0.72	0.60

NS: neck/shoulder girdle factor; GT: gluteal/trochanteric factor; UE: upper extremity factor; CON: control factor; h²: portion of variance in each variable accounted for by the solution.

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Table 4.

Demographic characteristics of patients with fibromyalgia (FM) by cluster group for Sample 1 (n = 690). Values are expressed as mean (SD) unless otherwise indicated.

Variable	HH, n = 223	ML, n = 268	LL, n = 199	Total, n = 690	p	h²
Average age, yrs	50.27 (10.69)	49.59 (10.81)	46.70 (13.16)	48.98 (11.58)	0.004	0.01
Female, %	215 (96.4)	251 (94.4)	185 (93.4)	651 (94.8)	0.37
Duration of FM, mo	121.1 (92.25)	115.71 (101.76)	106.15 (91.94)	114.71 (96.01)	0.28
BMI, weight/height, m²	30.45 (7.26)	30.91 (7.6)	30.27 (6.55)	30.58 (7.2)	0.61

h²: portion of variance in each variable accounted for by the solution. BMI: body mass index.

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Table 5.

Psychosocial characteristics by cluster group for Sample 1 (n = 690). Values are expressed as mean (SD).

Variable	HH (n = 223)	ML (n = 268)	LL (n = 199)	Total (n = 690)	p	h²
Pain score (0–10)	7.58 (1.23)	6.69 (1.19)	6.42 (1.35)	6.9 (1.34)	< 0.001	0.13
Sleep score (0–10)	7.05 (1.61)	6.36 (1.53)	6.0 (1.54)	6.48 (1.61)	< 0.001	0.07
FIQ physical impairment (0–3)	1.35 (0.69)	1.20 (0.7)	1.09 (0.64)	1.22 (0.69)	0.001	0.02
HADS Anxiety	10.14 (4.57)	8.72 (4.36)	8.96 (4.23)	9.25 (4.43)	< 0.001	0.02
HADS Depression	8.42 (4.4)	7.53 (4.37)	6.83 (3.84)	7.62 (4.28)	< 0.001	0.02
Manual tender point count	17.79 (0.64)	17.06 (1.47)	15.72 (2.31)	16.91 (1.78)	< 0.001	0.21

FIQ: Fibromyalgia Impact Questionnaire; HADS: Hospital Anxiety and Depression Scale; h²: portion of variance in each variable accounted for by the solution.