Distinct pain profiles in patients with chronic obstructive pulmonary disease

Figures & data

Table 1 Characteristics in the total sample at enrollment into the study (n=267)

Characteristics	Mean (SD)	Range
Age (years)	63.2 (9.0)	37–84
FEV1 (liters)	1.0 (0.6)	0.2–2.9
FEV1 % predicted	38.9 (19.3)	10.4–80.0
Number of years with COPD	7.6 (6.3)	0–35
Pack-years smoking	35.7 (22.3)	0.3–160
Number of comorbidities	2.3 (1.7)	0–11
BMI (kg/m^2)	23.9 (4.6)	14.9–37.7
6MWT (meters)	378.8 (131.5)	36–720
	n	(%)
Sex
Male	126	(47.2)
Female	141	(52.8)
Cohabitation
Living with someone	175	(66.3)
Living alone	89	(33.7)
Education
Primary	96	(36.8)
Secondary	136	(52.1)
University/college	29	(11.1)
Smoking
Current	64	(24.0)
Previous	200	(74.9)
Never	3	(1.1)
Disease severity based on GOLD criteria
Moderate	83	(31.1)
Severe	61	(22.8)
Very severe	123	(46.1)

Abbreviations: BMI, body mass index; FEV₁, forced expiratory volume in one second; FEV₁%, forced expiratory volume in one second as a percentage of the predicted value; GOLD, Global Initiative for Chronic Obstructive Lung Disease; 6MWT, 6 Minute Walk Test.

Table 2 Latent class profile analysis solutions and fit indices for the 1-class through 3-class solutions for probability of occurrence of pain and severity of worst pain

Model	LL	AIC	BIC	Entropy	VLMR
Pain occurrence
1-class	−505.66	1,021.32	1,037.94	N/A	N/A
2-classa	−442.61	907.22	943.78	0.70	126.10*
3-class	−439.76	913.52	970.01	0.73	5.70^NS
Pain severity
1-class	−1,541.10	3,110.20	3,156.58	N/A	N/A
2-classb	−1,492.67	3,025.35	3,091.61	0.68	96.85
3-class	−1,476.31	3,004.63	3,090.77	0.77	32.71^NS

Notes:

* p<0.0001.

a The 2-class solution was selected for pain occurrence because the BIC for that solution was lower than the BIC for both the 1- and 3-class solutions. In addition, the VLMR was significant for the 2-class solution, indicating that 2-classes fit the data better than 1-class, but the VLMR was not significant for the 3-class solution, indicating that too many classes had been extracted. In addition, the 3-class solution resulted in a third, very small class (14 cases, 6.8% of the sample in the model) that is unlikely to generalize to other samples.

b The 2-class solution was selected for pain severity because the BIC for that solution was lower than the BIC for the 1-class solution. In addition, the VLMR was significant for the 2-class solution, indicating that 2-classes fit the data better than 1-class, but the VLMR was not significant for the 3-class solution, indicating that too many classes had been extracted. In addition, the 3-class solution resulted in a third, very small class (9 cases, 4.6% of the sample in the model) that is unlikely to generalize to other samples.

Abbreviations: AIC, Akaike’s Information Criterion; BIC, Bayesian Information Criterion; LL, log-likelihood; N/A, not applicable; ^NS, not significant; VLMR, Vuong-Lo-Mendell-Rubin likelihood ratio test for the K vs K-1 model.

Figure 1 Probability of pain occurrence in the two latent classes across five assessments.

Table 3 Differences in demographic and clinical characteristics, and health-related quality of life among the three latent pain groups based on probability of occurrence of pain

Characteristic	No pain (1)	Moderate probability of pain (2)	High probability of pain (3)	Statistics
	23.2% (n=62)	28.8% (n=77)	47.9% (n=128)
	Mean (SD)	Mean (SD)	Mean (SD)
Age (years)	62.4 (8.5)	62.1 (8.4)	64.2 (9.6)	F=1.56, p=0.213
SCQ score (0–57)	2.4 (2.4)	3.7 (3.0)	6.4 (4.4)	F=28.44, p<0.001, 3>1 and 2
Number of comorbidities	1.3 (1.2)	2.0 (1.5)	3.0 (1.8)	F=28.27, p<0.001, 3>2>1
Number of years since diagnosis of COPD	7.3 (6.2)	7.2 (5.9)	8.1 (6.5)	F=0.47, p=0.627
BMI (kg/m^2)	22.7 (4.2)	24.2 (4.7)	24.4 (4.6)	F=3.20, p=0.043, 3>1
FEV1 (liters)	0.9 (0.6)	1.1 (0.6)	1.1 (0.6)	KW, p=0.053
FEV1 % predicted	31.5 (16.8)	39.3 (19.0)	42.2 (19.8)	KW, p=0.001, 3>1 and 2
6MWT (meters)	386.9 (140.6)	394.2 (143.3)	364.3 (117.6)	F=1.15, p=0.319
Number of pain locations	N/A	1.7 (2.7)	6.0 (5.3)	t=−7.49, p<0.001
Pain inference (0–10)	N/A	1.4 (1.5)	3.5 (2.7)	t=−6.68, p<0.001
Symptoms (SGRQ, 0–100)	56.2 (21.6)	59.3 (20.3)	65.4 (19.7)	F=4.82, p=0.012, 3>1
Activity (SGRQ, 0–100)	70.3 (24.6)	70.5 (22.7)	70.7 (21.8)	F=0.01, p=0.994
Impact (SGRQ, 0–100)	40.1 (20.9)	43.8 (20.7)	48.3 (19.1)	F=3.41, p=0.035§
Total score (SGRQ, 0–100)	52.8 (20.1)	54.9 (18.2)	58.2 (17.3)	F=1.79, p=0.170
	% (n)	% (n)	% (n)
Sex				X^2=12.44, p=0.002, 3<1
Male*	64.5 (40)	49.4 (38)	37.0 (48)
Female	35.5 (22)	50.6 (39)	63.0 (80)
Cohabitation				X^2=3.84, p=0.156
Lives alone	24.6 (15)	32.5 (25)	38.9 (49)
Lives with someone	75.4 (46)	67.5 (52)	61.1 (77)
Education				KW, p=0.010, 3<1
Primary	23.3 (14)	39.0 (30)	41.9 (52)
Secondary	56.7 (34)	50.6 (39)	50.8 (63)
University	20.0 (12)	10.4 (8)	7.3 (9)
Smoking				X^2=3.48, p=0.159
Yes	96.8 (60)	100.0 (77)	99.2 (127)
No	3.2 (2)	0.0 (0)	0.8 (1)
Disease severity based on GOLD criteria				KW, p=0.019, 3<1
Moderate	16.2 (10)	35.0 (27)	36.0 (46)
Severe	25.8 (16)	18.2 (14)	24.2 (31)
Very severe	58.0 (36)	46.8 (36)	39.8 (51)
Comorbid conditions
Heart disease	10.2 (6)	12.9 (9)	25.9 (29)	X^2=8.33, p=0.015, 3>1
High blood pressure	29.3 (17)	23.6 (17)	34.8 (40)	X^2=2.65, p=0.262
Cancer	0.0 (0)	0.0 (0)	4.6 (5)	X^2=6.10, p=0.061
Diabetes	5.0 (3)	11.1 (8)	8.1 (9)	X^2=1.62, p=0.454
Ulcer or stomach disease	3.4 (2)	4.2 (3)	8.4 (9)	X^2=2.23, p=0.360
Bowel disease	1.7 (1)	4.3 (3)	6.5 (7)	X^2=1.95, p=0.385
Kidney disease	1.7 (1)	1.4 (1)	2.8 (3)	X^2=0.44, p=0.861
Liver disease	0.0 (0)	0.0 (0)	0.9 (1)	X^2=1.20, p=1.000
Anemia or other blood disease	0.0 (0)	2.9 (2)	1.9 (2)	X^2=1.60, p=0.593
Headache	8.5 (5)	22.9 (16)	32.4 (35)	X^2=12.14, p=0.002, 3>1
Depression	15.0 (9)	24.3 (17)	33.0 (37)	X^2=6.76, p=0.036, 3>1
Osteoarthritis	3.5 (2)	10.0 (7)	31.5 (35)	X^2=24.37, p<0.001, 3>1 and 2
Back and neck pain	8.5 (5)	43.1 (31)	68.7 (79)	X^2=57.36, p<0.001, 3>2>1
Rheumatoid arthritis	5.2 (3)	2.9 (2)	5.5 (6)	X^2=0.72, p=0.727
Disease of muscle/connective tissue	1.7 (1)	2.9 (82)	15.7 (17)	X^2=13.47, p=0.001, 3>1 and 2
Skin diseases	12.1 (7)	17.1 (12)	17.7 (20)	X^2=0.96, p=0.638

Note:

* Reference group.

§ indicates significant differences among the latent classes, but no significant pairwise group differences.

Abbreviations: BMI, body mass index; FEV₁, forced expiratory volume in one second; FEV₁%, forced expiratory volume in one second as a percentage of the predicted value; GOLD, Global Initiative for Chronic Obstructive Pulmonary Disease; KW, Kruskal–Wallis test; N/A, not applicable; SCQ, self-administered comorbidity questionnaire; SGRQ, St George Respiratory Questionnaire; 6MWT, 6 Minute Walk Test.

Figure 2 Severity of worst pain in the two latent classes across five assessments.

Table 4 Differences in demographic and clinical characteristics, and health-related quality of life among the three latent pain groups based on ratings of severity of worst pain

Characteristics	No pain (1) 24.0% (n=64)	Mild pain (2) 39.3% (n=105)	Moderate pain (3) 36.7% (n=98)	Statistics
	Mean (SD)	Mean (SD)	Mean (SD)
Age (years)	62.3 (8.4)	62.9 (8.4)	64.1 (10.0)	F=0.84, p=0.432
SCQ score (0–57)	2.3 (2.4)	4.0 (3.1)	6.9 (4.6)	F=32.91, p<0.001, 3>2>1
Number of comorbidities	1.2 (1.2)	2.2 (1.4)	3.2 (1.9)	F=32.01, p<0.001, 3>2>1
Number of years since diagnosis of COPD	7.3 (6.1)	7.7 (6.2)	7.8 (6.5)	F=0.09, p=0.919
BMI (kg/m^2)	22.7 (4.1)	24.1 (4.6)	24.6 (4.7)	F=3.62, p=0.028, 3>1
FEV1 (liters)	0.9 (0.6)	1.0 (0.5)	1.2 (0.6)	KW, p=0.004, 3>1
FEV1 % predicted	31.1 (16.6)	37.6 (18.4)	45.3 (19.9)	KW, p<0.001, 3>1 and 2
6MWT (meters)	385.3 (139.8)	376.7 (130.6)	376.5 (128.2)	F=0.09, p=0.918
Number of pain locations	N/A	2.5 (3.0)	6.5 (5.7)	t=−6.15, p<0.001
Pain inference (0–10)	N/A	1.6 (2.0)	4.0 (2.6)	t=−6.70, p<0.001
Symptoms (SGRQ, 0–100)	57.0 (21.7)	60.9 (20.8)	65.2 (19.2)	F=3.10, p=0.047§
Activity (SGRQ, 0–100)	70.4 (24.3)	70.9 (21.7)	70.3 (22.7)	F=0.02, p=0.982
Impact (SGRQ, 0–100)	41.0 (21.3)	45.5 (20.5)	47.2 (18.9)	F=1.77, p=0.173
Total score (SGRQ, 0–100)	53.5 (20.2)	56.0 (18.6)	57.7 (16.5)	F=0.92, p=0.399
	% (n)	% (n)	% (n)
Sex				X^2=11.28, p=0.004, 3<1
Male*	62.5 (40)	48.6 (51)	35.7 (35)
Female	37.5 (24)	51.4 (54)	64.3 (63)
Cohabitation				X^2=3.08, p=0.216
Lives alone	25.0 (16)	34.0 (35)	38.8 (38)
Lives with someone	75.0 (47)	66.0 (68)	61.2 (60)
Education				KW, p=0.005, 3 and 2<1
Primary	22.5 (14)	39.4 (41)	43.2 (41)
Secondary	56.5 (35)	53.9 (56)	47.4 (45)
University	21.0 (13)	6.7 (7)	9.4 (9)
Smoking				X^2=3.51, p=0.185
Yes	96.9 (62)	100.0 (105)	99.0 (97)
No	3.1 (2)	0.0 (0)	1.0 (1)
Disease severity based on GOLD criteria				KW, p<0.001, 3<1 and 2
Moderate	15.6 (10)	29.5 (31)	42.9 (42)
Severe	25.0 (16)	18.1 (19)	26.5 (26)
Very severe	59.4 (38)	52.4 (55)	30.6 (30)
Comorbid conditions
Heart disease	9.8 (6)	15.3 (15)	28.0 (23)	X^2=8.74, p=0.012, 3>1
High blood pressure	28.3 (17)	24.5 (24)	37.9 (33)	X^2=4.08, p=0.132
Cancer	0.0 (0)	1.0 (1)	5.0 (4)	X^2=5.08, p=0.072
Diabetes	4.8 (3)	7.1 (7)	12.0 (10)	X^2=2.70, p=0.266
Ulcer or stomach disease	3.3 (2)	6.1 (6)	7.6 (6)	X^2=1.13, p=0.575
Bowel disease	1.7 (1)	3.1 (3)	8.8 (7)	X^2=4.73, p=0.107
Kidney disease	1.7 (1)	1.0 (1)	3.8 (3)	X^2=1.65, p=0.532
Liver disease	0.0 (0)	1.0 (1)	0.0 (0)	X^2=1.45, p=1.000
Anemia or other blood disease	0.0 (0)	1.1 (1)	3.7 (3)	X^2=3.26, p=0.195
Headache	8.2 (5)	22.9 (22)	36.2 (29)	X^2=15.14, p<0.001, 3>1
Depression	16.1 (10)	25.3 (24)	34.1 (29)	X^2=6.07, p=0.048§
Osteoarthritis	3.4 (2)	13.7 (13)	34.5 (29)	X^2=24.70, p<0.001, 3>1 and 2
Back and neck pain	8.2 (5)	49.0 (48)	71.3 (62)	X^2=57.62, p<0.001, 3>2>1
Rheumatoid arthritis	5.0 (3)	1.0 (1)	8.6 (7)	X^2=5.76, p=0.051
Disease of muscle/connective tissue	1.7 (1)	5.4 (5)	17.1 (14)	X^2=12.50, p=0.002, 3>1 and 2
Skin disease	11.7 (7)	18.6 (18)	16.7 (14)	X^2=1.32, p=0.562

Notes:

* Reference group;

§ indicates significant differences among the latent classes, but no significant pairwise group differences.

Abbreviations: BMI, body mass index; FEV₁, forced expiratory volume in one second; FEV₁%, forced expiratory volume in one second as a percentage of the predicted value; GOLD, Global Initiative for Chronic Obstructive Pulmonary Disease; KW, Kruskal–Wallis test; N/A, not applicable; SCQ, self-administered comorbidity questionnaire; SGRQ, St George Respiratory Questionnaire; 6MWT, 6 Minute Walk Test.