Eur Spine J DOI 10.1007/s00586-014-3723-y

ORIGINAL ARTICLE

Evaluation of quality of life and neuropathic pain in patients with low back pain using the Japanese Orthopedic Association Back Pain Evaluation Questionnaire Akihiko Hiyama • Masahiko Watanabe • Hiroyuki Katoh • Masato Sato • Daisuke Sakai Joji Mochida



Received: 6 August 2014 / Revised: 7 December 2014 / Accepted: 8 December 2014 Ó Springer-Verlag Berlin Heidelberg 2014

Abstract Purpose To examine the impact that neuropathic or nociceptive pain has on the quality of life (QOL) in patients with low back pain (LBP) using the Japanese Orthopedic Association Back Pain Evaluation Questionnaire (JOABPEQ) and the Japanese version of the PainDETECT Questionnaire (PDQ-J). Methods Between June 2012 and December 2013, 650 new patients were treated at our institution for LBP. All patients between the ages of 20 and 79 were asked to complete a set of questionnaires including the PDQ-J, a pain visual analog scale (VAS), the JOABPEQ, and the Short Form 36 (SF-36). Based on the PDQ-J scores, participants were classified into three groups: a neuropathic pain group, a nociceptive pain group, and an intermediate mixed pain group. Among them, patients with clear neuropathic and nociceptive LBP were selected. To investigate the differences between neuropathic and nociceptive LBP,

diagnosis of spinal disorder, prevalence, age, gender, duration of symptoms, VAS scores, and self-reported general health (SF-36 and JOABPEQ) were compared between the neuropathic and nociceptive pain groups. Results Of 650 patients with LBP, 331 completed the questionnaires and were enrolled in the study. There were 193 men (58.3 %) and 138 women (41.7 %) with a mean age of 54.5 years (range 20–79 years). From the PDQ-J survey, 49 patients (15 %) were classified as having neuropathic pain, and 190 (58 %) were categorized as having nociceptive pain. Patients in the neuropathic pain group had significantly higher VAS scores and lower SF-36 and JOABPEQ scores compared to the nociceptive pain group. Conclusion We examined the impact of nociceptive or neuropathic LBP on QOL. A comparison of JOABPEQ scores between LBP patients assessed by PDQ-J as having neuropathic pain or nociceptive pain suggests that neuropathic pain affects the social and psychological well-being of LBP patients.

A. Hiyama (&)  M. Watanabe  H. Katoh  M. Sato  D. Sakai  J. Mochida Department of Orthopaedic Surgery, Surgical Science, Tokai University School of Medicine, 143 Shimokasuya, Isehara, Kanagawa 259-1193, Japan e-mail: [email protected]

Keywords PainDETECT (PDQ)  Low back pain (LBP)  JOA Back Pain Evaluation Questionnaire (JOABPEQ)  Neuropathic pain  Quality of life (QOL)

M. Watanabe e-mail: [email protected]

Introduction

H. Katoh e-mail: [email protected]

Low back pain (LBP) is a common ailment, with roughly 60–80 % of the adult population in the US estimated to have LBP. It is the second most frequent reason for people to go to see a doctor, both in the US and in Japan, and it is the leading cause of disability [1]. The complaint of LBP is varied, often making a precise diagnosis difficult. LBP persisting for more than 3 months is referred to as chronic LBP, and has an increased association with psychological

M. Sato e-mail: [email protected] D. Sakai e-mail: [email protected] J. Mochida e-mail: [email protected]

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factors. It is, therefore, essential for the physician to be able to diagnose accurately the pain characteristics of the LBP patient at an early stage, so that an appropriate treatment may be initiated and a transition to chronic LBP avoided. Although the pain has been categorized into a variety of ways, one classification that has been particularly useful is that of nociceptive and neuropathic pain. Nociceptive pain results from activity in neural pathways caused by tissue injury or potential tissue-damaging stimuli such as surgery and arthritis. Mechanical LBP is considered to be a mainly nociceptive pain. In contrast, neuropathic pain is defined as pain arising as a direct consequence of a primary lesion or disease affecting the somatosensory system [2]. Diabetic peripheral neuropathy, postherpetic neuralgia, complex regional pain syndrome, and neuropathic back and leg pain are considered to be examples of neuropathic pain [3, 4]. Neuropathic pain can be acute in nature, but is often persistent and difficult to treat [5]. Although the mechanisms that lead to neuropathic pain are still being investigated, excess stimulation of nociceptive pathways and damage to inhibitory pathways are believed to alter the balance between painful and non-painful sensory inputs, eliciting pain even in the absence of nociceptive stimulation [6]. LBP often comprises both nociceptive pain and neuropathic pain, and large epidemiological studies show that 20–35 % of patients with LBP suffer from neuropathic pain [7]. O’Connor et al. [8] reported that neuropathic pain profoundly impairs the quality of life (QOL) and that patients with neuropathic pain are likely to have more medical expenses than those with other painful conditions. Therefore, it is important to clarify the involvement of neuropathic and nociceptive pain in patients with LBP and to tailor the approaches to treatment. However, the diagnosis and treatment of neuropathic and nociceptive pain remain an enigma, mainly because of the lack of a standard tool to evaluate neuropathic and nociceptive pain in patients with LBP. Although various clinical scales have been developed for diagnosing neuropathic pain [e.g., the Leeds assessment of neuropathic symptoms and signs (LANSS), and Douleur Neuropathique en 4 Questions (DN4)] [9, 10], their complexity makes routine clinical application impractical. The painDETECT (PDQ) has been a recently developed screening tool designed to detect neuropathic pain in chronic LBP patients based on their self-reported pain characteristics [11]. On the basis of verbal symptom descriptors, this tool distinguishes neuropathic pain from non-neuropathic pain with 85 % sensitivity and 80 % specificity, slightly higher than the conventional questionnaires DN4 and LANSS. The purpose of this study was to evaluate the percentage of neuropathic pain, mixed pain and nociceptive pain in new outpatient LBP patients using the Japanese version of

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the PDQ (PDQ-J) and to examine the effects of neuropathic and nociceptive LBP patients on the QOL.

Materials and methods Ethics statement and subjects The Committee on Ethics and the Institutional Review Board of Tokai University School of Medicine approved the study protocol (Approved number: 13R238) and all enrolled patients gave written consent. This investigation was designed as a single-center retrospective comparative study of LBP patients at their first medical examination. Each patient was seen by two investigators. The first investigator proposed a diagnosis of LBP on the basis of interview performed according to his/ her usual practice, and gave the paper-based questionnaires to each patient. Thereafter, the second investigator proposed a diagnosis and treatment of LBP on the basis of an interview and examination performed according to his/her usual practice, and then collected the questionnaires. In all of the patients, the diagnosis was defined by more than one spine surgeon, including a co-author. The data obtained were gathered, transferred to a database (ExcelÒ) and then processed and evaluated. Between June 2012 and Dec 2013, 650 new patients were treated for LBP at our university hospital, which is a suburban tertiary care center. The inclusion criteria were: (1) patients aged between 20 and 79 years with a main complaint being LBP (pain between the 12th rib and buttock crease) with or without associated leg pain or numbness; (2) patients were able to understand the Japanese language; (3) patients who answered all questions on the self-administered questionnaires. Patients were excluded if they: (1) had signs of nerve root compromise, defined as sensory loss and severe motor deficits; (2) were diagnosed as having poor mental health problems or a metastatic tumor. Duration of LBP was not a factor for enrollment into this study. Diagnosis of nervous or somatic lesions was based on medical history and physical examination. In the first survey, all patients between the ages of 20 and 79 who visited the hospital complaining of LBP were asked to complete a set of paper-based self-administered questionnaires: the Japanese version of PDQ (PDQ-J) [12], a pain visual analog scale (VAS), the Japanese Orthopedic Association Back Pain Evaluation Questionnaire (JOABPEQ) [13–17] and the Short Form 36 (SF-36) [18]. The JOABPEQ consists of five subscales and the SF-36 consists of eight subscales; with both tests, a higher score means a better QOL.

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Questionnaires PainDETECT-J The PDQ allows clinicians to evaluate the likelihood of a person’s LBP to have a neuropathic or non-neuropathic component, based on the following self-reported pain characteristics: the degree of the seven types of pain qualities, the type of pain pattern, and the presence of radiating pain. The PDQ has been translated into numerous languages [19, 20], and the PDQ-J has been reported to have similar reliability and validity to the original PDQ [12]. Cronbach’s alpha for the total score of the PDQ-J was 0.78 and that of the main component of the PDQ was 0.80, which was comparable to the 0.83 reported in the original report. Matsubayashi et al. [12] have encouraged researchers and clinicians to use the PDQ-J for the assessment of patients suffering from pain that is suspected to be neuropathic in origin. From the three components of the PDQ-J, a total score is calculated; a high score indicates that the pain is likely to have a neuropathic component. Using the cut off scores proposed by Freynhagen et al. [11], participants were classified into three groups: a group ‘‘likely’’ to have neuropathic pain (neuropathic pain group with scores C19), a group ‘‘unlikely’’ to have neuropathic pain (nociceptive pain group with scores B12), and an intermediate ‘‘mixed’’ group (scores 13–18). The percentage of neuropathic pain, mixed pain and nociceptive pain in new outpatient LBP patients using the PDQ-J was investigated. Among them, we focused on the patients with clear neuropathic and nociceptive LBP. To investigate the differences between the neuropathic and nociceptive pain groups, the spinal disorder diagnosed, age, gender, duration of symptoms, VAS scores, and QOL scores (SF-36 and JOABPEQ) were compared between the two groups. LBP was also classified by duration as acute/subacute (pain lasting less than 12 weeks) or chronic (more than 12 weeks). VAS score Also included in the PDQ-J are three visual analog scales with a range of 0–10 (0 = no pain, 10 = worst pain imaginable) to portray the current pain, the maximum pain during the past 4 weeks, and the average pain for the past 4 weeks.

functional scores (LBP, lumbar function, walking ability, social life function, and mental health) using the provided formulas or by entering the data into the Excel file that are available on the website of the Japanese Orthopedic Association (http://www.jssr.gr.jp/jssr_web/html/index.html). SF-36 The SF-36 v2 is a 36-item general health questionnaire that yields an 8-scale profile of health: physical function (PF), social function (SF), role-emotional (RE), role-physical (RP), bodily pain (BP), general health (GH), mental health (MH), and vitality (VT). These can be combined into three component summary measures: physical (PCS), mental (MCS), and role/social component summary measures (RCS). The scales are linearly transformed into a 0–100 scale, with 0 indicating the least favorable health state and 100 indicating the best state of health. The validity and reliability of the SF-36 have been tested extensively. Statistical analysis Statistical analysis was performed using SPSS version 20.0 (SPSS Inc., Chicago, IL). All values are expressed as mean ± standard deviation. An analysis of variance with a post hoc test (Mann–Whitney U test) and student’s t test were used for comparisons. Normally distributed variables were compared using the student’s t test and non-normally distributed variables were compared using Mann–Whitney U test. For gender and age, the number of cases and the percentage were compared using the student’s t test. Oneway ANOVA was used to compare the LBP patients grouped according to pain duration (acute/subacute and chronic LBP) and pain classification (neuropathic and nociceptive LBP). To identify the minimum number of participants required for adequate statistical power, we used the G-Power Analysis software program (G Power 3.1.9, University of Du¨sseldorf, Germany, http://www. gpower.hhu.de/.) [21]. A power analysis performed to calculate the minimum sample size necessary to detect a difference between two independent groups (calculated with Cohen’s d = 0.8, alpha = 0.05, two-tailed, power = 0.8) indicated a required sample size of 26 participants per group, for a total of 52. For all statistical analyses, type 1 error was set at 5 % and p \ 0.05 was considered significant.

JOABPEQ

Results

JOABPEQ is a patient-based measure of health-related QOL for patients with low back disorders [13–17]. From the answers to 25 questions, the examiner calculates five

Of the 650 new patients with LBP, 331 patients were enrolled in this study, resulting in a recruitment rate of 50.9 %. Following exclusion criteria, 72 patients were

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excluded in this study. Furthermore, LBP patients with missing questionnaire data for the PDQ-J, JOABPEQ and SF-36 were excluded from this study. A surprisingly large number of 247 patients were excluded because of incomplete responses to proposed question; most of the blank responses for the PDQ-J were to the question regarding the presence of radiating pain. There were 193 men and 138 women with a mean age of 54.5 years (range 20–79 years) (Fig. 1). Of the 331 patients with LBP, 135 patients (40.8 %) showed symptoms in the lower limbs, such as leg pain and/or numbness, etc. From the PDQ-J survey, 49 patients were classified as having neuropathic pain and 190 as having nociceptive pain (Fig. 2a). The PDQ-J survey of the presence of lower limb symptoms indicated that 8 % (15/196) of patients with LBP without lower limb symptoms had neuropathic pain, while the percentage of neuropathic pain in patients with LBP who had lower limb symptoms was significantly higher at 25 % (34/135 patients) (Fig. 2b). Because it has been suggested that the percentage of neuropathic pain becomes higher in patients with chronic LBP, a survey of symptom duration was conducted, revealing neuropathic pain in 26 of the 130 (20 %) patients with chronic LBP and in 23 of the 201 (12 %) patients with acute/subacute LBP (Fig. 2c). The percentage of patients with chronic LBP was higher in those with lower limb symptoms (79/135 patients, 58.5 %) compared with that in patients without lower limb symptoms (51/196 patients, 26.0 %).

Fig. 1 Flow diagram of this study

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Table 1 shows the detailed demographics of the neuropathic and nociceptive pain groups. There was a significant difference in the age distribution: patients in the neuropathic pain group were significantly older than the patients in the nociceptive pain group (p \ 0.05) (Table 1). However, there was no significant difference in the mean age between the two groups (p = 0.241). The distribution of men and women was similar in the two groups (p = 0.344). The period between the onset of symptoms and the initial hospital visit tended to be longer in the neuropathic pain group compared with the nociceptive pain group. LBP was chronic in 53.1 % (26 of 49 patients) of the neuropathic pain group and in 33.2 % (63 of 190 patients) of the nociceptive pain group (p \ 0.05). The VAS pain intensity scores were significantly higher in the neuropathic pain group compared with the nociceptive pain group for both acute/subacute and chronic LBP (p \ 0.05) (Table 2). The diagnosis of lumbar disease outlined in Table 3 shows that lumbar disc herniation was the most prevalent diagnosis in the neuropathic pain group (36.7 %), while non-specific LBP was most prevalent in the nociceptive pain group (44.2 %). Because the neuropathic pain group had more severe pain for longer periods, we examined its effect on QOL by comparing SF-36 and JOABPEQ scores between the two groups. Evaluation of SF-36 scores demonstrated that in patients with neuropathic pain, all eight scales showed lower values, regardless of the presence of lower limb

Eur Spine J Fig. 2 The percentage of neuropathic pain, nociceptive pain and mixed pain components. a The PDQ-J survey of total patients. b The PDQ-J survey of the presence of lower limb symptoms. c The PDQ-J survey of symptom duration

Table 1 Detailed demographics of the patients in the two groups (neuropathic LBP group and nociceptive LBP group) Characteristic (n)

NeP (49)

NocP (190)

PainDETECT (PDQ-J)

23.0 ± 3.6

7.5 ± 3.6

Age (years) 20–29

4a

8.2b

24a

12.6b

30–39

a

b

a

12.6b

a

12.6b

a

13.7b

a

28.9b

a

19.5b

40–49 50–59 60–69 70–79

3

6.1

a

24 b

5

10.2 a

14

a

12

a

11

b

28.6

b

24.5

b

22.4

24 26 55 37

Mean age ± SD (years)

57.3 ± 14.9

53.5 ± 16.9

Sex (male/female)

26/23

115/75

Duration of symptom (chronic [12 weeks)

26a

53.1b

63a

NeP neuropathic pain group, NocP nociceptive pain group a

Number

b

Percentage

33.2b

symptoms, compared with those for nociceptive pain (Fig. 3a). Next, when evaluating whether the presence of lower limb symptoms affected the QOL of the neuropathic pain group and the nociceptive pain group, respectively, we found that the QOL score was lower when lower limb symptoms were present, but this difference was not significant. The SF-36 scores evaluating the duration of pain, also shown in Fig. 3b, reveal that patients with neuropathic pain scored significantly lower than those with nociceptive pain on all eight scales and on the PCS and RCS summary measures, but not the MCS summary measure. JOABPEQ scores also revealed that patients in the neuropathic pain group had lower QOL scores compared with the nociceptive pain group, for patients with both acute/subacute and chronic LBP (Table 4). While all QOL parameters were lower in the neuropathic pain group, it is interesting to note that the difference between the two groups in the walking ability parameter was greater than

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Eur Spine J Table 2 VAS scores for three time points (i.e., pain at the time of initial visit, the maximum pain experienced during the prior 4 weeks and the average pain for that period) Outcomes (n)

NeP (23)

NocP (127)

(n)

Acute/subacute (201)

p value

NeP (26)

NocP (63)

p value

Chronic (130)

VAS (present)

8.5 ± 1.3

5.7 ± 2.1

*

8.1 ± 1.8

5.0 ± 2.3

*

VAS (maximum)

8.8 ± 1.1

6.5 ± 2.8

*

8.5 ± 1.6

6.6 ± 2.3

*

VAS (average)

6.7 ± 2.1

4.4 ± 2.3

*

7.4 ± 1.9

5.1 ± 2.0

*

Score = mean ± SD The single asterisk (*p \ 0.05) indicates significant differences between the neuropathic and nociceptive LBP groups NeP neuropathic pain group, NocP nociceptive pain group, n number of patients

Table 3 Lumbar disease diagnosis of patients in the two groups (neuropathic pain group and nociceptive pain group) Diagnosis

NeP

NocP

No.of patients

%

No.of patients

%

7 18

14.3 36.7

84 13

44.2 6.8

Spondylosis

6

12.2

40

21.1

Spinal canal stenosis

5

10.2

25

13.2

Degenerative spondylolisthesis

4

8.2

10

5.3

Non-specific LBP Lumbar disc herniation

Compression fracture

5

1.0

5

2.6

Degenerative scoliosis

2

4.1

5

2.6

Spondylolysis/ spondylolisthesis Spondylitis

0

0.0

2

1.1

0

0.0

1

0.5

Spinal tumor

0

0.0

0

0.0

Other disease

2

4.1

5

2.6

NeP neuropathic pain group, NocP nociceptive pain group

for other parameters. Upon evaluating the JOABPEQ with respect to the presence of lower limb symptoms, the QOL of the neuropathic pain group was lower than the nociceptive pain group, regardless of whether lower limb symptoms were present (Table 5). Focusing on the walking ability parameter, when lower limb symptoms were present, both neuropathic and nociceptive pain groups had low scores, but only the nociceptive pain group showed a statistically significant difference. This indicated that the presence of lower limb symptoms associated with LBP may affect the walking ability parameter in JOABPEQ.

Discussion The incidence of The International Association for the Study of Pain defined neuropathic pain as ‘‘pain initiated or caused by a primary lesion or dysfunction in the nervous system.’’ Although this definition appears simple, the lack

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of anatomic precision and diagnostic specificity has hindered progress in the diagnosis, classification, and treatment of neuropathic pain, because many pain conditions display symptoms of neuropathic pain, but do not meet this criterion. Debate concerning the appropriateness of this definition led Treede et al. [2] to propose a revised definition of neuropathic pain as ‘‘pain arising as a direct consequence of a lesion or disease affecting the somatosensory system’’. LBP is common and a significant number of people in the general population appear to suffer from LBP. In 2010, Hoy et al. [22] published a systematic review of the prevalence of LBP. In this review, 1-year incidence of a first-ever episode of LBP ranges between 6.3 and 15.4 %, while estimates of the 1 year incidence of any episode of LBP range between 1.5 and 36 % [22]. While LBP is generally a combination of neuropathic and nociceptive pain in varying degrees, patients with predominantly neuropathic pain often have severe, chronic symptoms that decrease their QOL. As mentioned above, nociceptive LBP is caused by injury and/or inflammatory process associated with actual or potential tissue damage, while neuropathic LBP results from a lesion or a malfunction within the nervous system. However, it is difficult to distinguish the specific clinical difference between patients with nociceptive and neuropathic LBP. Although the need to identify and effectively manage neuropathic pain in LBP patients is well understood, the strict clinical diagnosis of neuropathic pain is based on the evidence of a lesion or disease of the somatosensory system, ascertained primarily by interviewing the patient and performing clinical examinations [2]. However, the need for a simpler means to diagnose neuropathic pain led to the development of standardized screening tools that distinguish neuropathic pain on the basis of patient-reported verbal pain descriptors which can be conducted with a limited interview and bedside examination. The identification of neuropathic pain using such screening tools has enabled clinicians to evaluate the involvement of neuropathic pain and to implement a more direct and specialized management strategy for these

Eur Spine J Fig. 3 SF-36 scores for the lower limb symptoms (a) or pain period (b) in the neuropathic and nociceptive pain groups. Eight multi subscales (PF physical function, RP role-physical, BP bodily pain, GH general health, VT vitality, SF social function, RE role-emotional, MH mental health) three summary measures (PCS physical component summary, MCS mental component summary, RCS role/ social component summary) NeP neuropathic pain group, NocP nociceptive pain group, n number of patients. *p \ 0.05 indicates significant differences between the neuropathic and nociceptive LBP groups., n.s. not significant

Table 4 JOABPEQ scores for acute/subacute and chronic LBP patients in the neuropathic and nociceptive pain groups

Table 5 JOABPEQ scores for LBP patients with or without leg pain in the neuropathic and nociceptive pain groups

Acute/subacute (n)

NeP (23)

NocP (127)

p value

NeP (15)

Low back pain

29 (23.7 ± 25.6)

43 (50.2 ± 31.5)

*

Lower limb symptoms (-) (n)

Lumbar function Walking ability

33 (29.7 ± 19.6) 29 (33.2 ± 27.8)

50 (54.7 ± 28.3) 64 (59.4 ± 29.4)

* *

Low back pain

29 (25.7 ± 27.5)

43 (49.3 ± 31.9)

*

Social life function

35 (29.6 ± 17.7)

51 (52.3 ± 22.0)

*

Lumbar function

33 (26.1 ± 17.5)

58 (56.6 ± 30.5)

*

Mental health

36 (32.4 ± 16.6)

51 (49.9 ± 17.4)

*

NocP (63)

p value

29 (24.8 ± 22.3)

43 (48.5 ± 32.3)

*

37.5 (34.7 ± 32.3)

75 (65.2 ± 29.9)

*

Chronic (n) Low back pain Lumbar function Walking ability

NeP (26)

21 (33.7 ± 33.2)

64 (59.4 ± 32.0)

*

Social life function

39.5 (35.8 ± 27.5)

51 (53.1 ± 25.4)

*

Mental health

38.5 (35.1 ± 20.4)

48 (49.2 ± 18.4)

*

Score = median (mean ± SD) The single asterisk (* p \ 0.05) indicates significant differences between the neuropathic and nociceptive LBP groups NeP neuropathic pain group, NocP nociceptive pain group, n number of patients

patients. The PDQ is a simple and reliable screening tool that was developed to assess the likelihood of a neuropathic pain component in patients with LBP, and it is reported to have slightly higher sensitivity and specificity compared with other screening tools for neuropathic pain. The selfadministered questionnaires are easier to standardize because the possibility of systematic differences in

NocP (142)

p value

Walking ability

43 (40.0 ± 31.2)

71 (62.4 ± 30.7)

*

Social life function

35 (35.5 ± 21.0)

51 (53.0 ± 23.9)

*

Mental health

36 (35.0 ± 13.1)

51.5 (50.4 ± 18.5)

*

NocP (48)

p value

Lower limb symptoms (?) (n)

NeP (34)

Low back pain

29 (23.6 ± 22.2)

43 (50.5 ± 31.3)

Lumbar function

37.5 (35.1 ± 30.0)

62.5 (62.9 ± 24.8)

*

Walking ability

21 (30.6 ± 30.1)

46.5 (50.7 ± 27.1)

*

Social life function

38 (31.7 ± 24.6)

51 (51.4 ± 20.7)

*

Mental health

37 (33.4 ± 20.7)

48 (47.5 ± 14.9)

*

Score = median (mean ± SD) The single asterisk (* p \ 0.05) indicates significant differences between the neuropathic and nociceptive LBP groups NeP neuropathic pain group, NocP nociceptive pain group, n number of patients

interviewing technique is avoided. On the other hand, they are limited by the need to be unambiguously understood by all patients. Thus, a disadvantage of self-administered

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questionnaires is their low response rate, which in this case was 57.3 % (331 complete versus 247 incomplete questionnaires). Because self-administered questionnaires (PDQ-J, SF-36, and JOABPEQ) require adequate reading and comprehension skills, the fact that 300 of the 650 LBP patients were 65 years of age or above may partially explain the low rate of completed questionnaires. This study reports a number of unique findings from the use of the PDQ-J screening questionnaire in the Japanese population. The percentage of neuropathic pain in patients with LBP was 14.8 %, which is similar to that found by Morso et al. (19.3 %) [23] and Beith et al. (16.0 %) [24]. In studies conducted using different screening questionnaires such as the DN4 and LANSS in Europe and the US, neuropathic pain in the general population (not specific for LBP) was reported to be 3–9 % [25–27]. Another study conducted in Saudi Arabia using the LANSS reported a neuropathic component in 55 % of LBP patients [28]. Studies from Germany using the PDQ reported 37 and 36 % prevalence rates of neuropathic pain in patients with LBP [11, 29]. Apart from the obvious differences that would arise when other questionnaires are utilized to evaluate neuropathic pain, variability in results may arise from different pathoanatomy, cultural differences, or translation imperfections in different language versions of the PDQ. The rate of neuropathic pain is higher in patients with chronic LBP, suggesting that neuropathic pain may be deeply involved in chronic LBP. In addition to the increase in the rate of neuropathic pain in the chronic LBP group, there is a significant increase in the number of patients with mixed pain with an overall decrease in patients in the nociceptive pain group. This suggests that some patients who started out with nociceptive pain developed neuropathic pain over time, causing them to be recategorized into the ‘‘mixed pain group’’, and LBP may be associated with neuropathic pain in some cases when some kind of damage to the peripheral nervous tissue in the lumbar spine is present or neuroplastic changes have developed in the synapses of the dorsal horn of the spinal cord as a result of prolonged afferent signal from nociceptors. VAS scores also revealed that the neuropathic pain group experienced pain that was significantly more severe than that in the nociceptive pain group. A previous study also found that patients with more severe pain recorded a higher total score on PDQ-J [12], suggesting that stronger pain may lead to a higher involvement of a neuropathic component. The QOL of LBP patients was evaluated using the JOABPEQ and SF-36 scores, revealing that patients suffering from neuropathic pain had impaired physical and mental QOL. Although the medians for the five categories of the JOABPEQ were distributed around 50 as reported

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by Ohtori et al. [17], patients with neuropathic pain had significantly lower scores in all five categories compared with patients with nociceptive pain, suggesting that neuropathic pain decreases QOL and affects the social life of LBP patients. Scores for physical and mental components of the SF-36 were significantly lower in neuropathic pain patients with both acute/subacute and chronic LBP, confirming the findings of Freynhagen et al. [11]. These results might indicate its action for neuropathic pain. In a previous study, Beith et al. [24] also demonstrated that patients with neuropathic pain have lower QOL compared with other pain groups, with significantly greater pain, disability, anxiety and depression. While all parameters of the JOABPEQ were lower in the neuropathic pain group, the difference between the two groups in scores for walking ability was especially large. Because neuropathic pain arises from nerve root compression or irritation, certain activities and positions, such as walking, may lead to aggravation of the nerve root and increased pain. In the present study, the presence of lower limb symptoms affected the walking ability score on the JOABPEQ, which once again indicated that in the case of neuropathic pain, many patients present with lower limb symptoms. Therefore, the JOABPEQ score for walking ability may be lower in LBP patients with neuropathic pain than in patients with nociceptive pain. Ohtori et al. [17] also reported significant differences in average JOABPEQ scores depending on age, sex, and type of disease diagnosed. Because the patients with neuropathic pain were older than the patients with nociceptive pain and were diagnosed with different spine diseases, these factors may have affected the scores. Recently, Yamashita et al. [30] reported that logistic regression analysis identified the following risk factors for the presence of spine-related neuropathic pain in the Japanese population: advanced age, severe pain, disease duration longer than 6 months, and a cervical lesion. These risk factors suggest that the more severe is the damage to the nerve tissue, the higher is the incidence of neuropathic pain. The limited number of patients in the neuropathic pain group in this study made it difficult to reach any conclusive results using logistic regression analysis. We plan to perform additional studies with a larger sample size to include a sufficient number of participants with neuropathic LBP.

Limitations This study has several limitations. First, the involvement of neuropathic pain in this study was determined solely on the basis of the PDQ-J. As there is an ongoing debate about the definition of neuropathic pain, a consensus on the most

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appropriate screening tool remains to be reached. Despite good sensitivity and specificity of the PDQ, the question remains whether the distinction between neuropathic and nociceptive symptom profiles truly represents the biological background of pain or whether it may be an artificial effect. Although screening tools may give guidance to clinicians by selecting patients who need further diagnostic evaluation and pain management by specialists, they clearly do not replace clinical judgment. Furthermore, PDQ was originally validated in a population of pain patients seeking medical opinion; further validation in the general population is needed. The second limitations of this study include that it is a single-center retrospective study conducted at a tertiary care university hospital, limiting generalizability; possible unmeasured residual confounding; and small numbers of patients with neuropathic and nociceptive LBP. The spectrum of presenting patients obviously differs between primary care clinics, community hospitals, and tertiary care facilities. Furthermore, the location of our university hospital in the suburbs of Tokyo may also be a factor in limitation; Bouhassira et al. and Torrance et al. [25, 27] reported that neuropathic pain is more prevalent in unemployed rural dwellers and those with a lower professional or educational status. A multicenter study, including a spectrum of medical facilities spanning both metropolitan and rural areas may solve this limitation. Third, because an identifiable lesion to the somatosensory nervous system has yet to be determined in LBP patients, there is insufficient evidence to suggest that neuropathic pain is a comorbid condition in LBP. Fourth, the sample size precluded further evaluation with multivariate analyses to uncover the factors that may result in lower QOL. Further study with a larger sample size may reveal factors other than old age. Fifth, the purpose of the present study was not to focus on non-specific LBP, but to serve as a retrospective study examining the QOL of patients initially diagnosed at our hospital with a main complaint being LBP, and the percentage thereof with neuropathic pain. For that reason, there are constraints on the subjects, because not just those with LBP, but also patients with lower limb symptoms are included. However, upon considering the QOL of patients with LBP because of the presence of lower limb symptoms, and the percentage thereof, with neuropathic pain, it was clear that regardless of whether or not lower limb symptoms were present, the QOL was lower for patients with neuropathic pain compared to patients with nociceptive pain. In the present study, nonspecific LBP and various diagnoses, such as intervertebral disc hernia, are included, so this is not a disease-specific study. Therefore, we believe that it will be necessary in the future to conduct a prospective study focused on nonspecific LBP.

Conclusions This study comparing the QOL between LBP patients with neuropathic pain and nociceptive pain suggests that neuropathic pain affects the social and psychological wellbeing of LBP patients. By using screening tools such as the PDQ, it is possible to evaluate the involvement of neuropathic pain at an early time point, which enables clinicians to implement a focused strategy to treat the pain and improve the QOL of LBP patients. This study was purely an observational study and was not planning to evaluate the proper dose regimen of any medications or the neuropathic and nociceptive LBP patient’s response to such treatment. Further studies will be necessary to investigate whether PDQ-J scores are predictive of treatment response when therapy is targeted to neuropathic and nociceptive LBP. Acknowledgments

No funds were received in support of this work.

Conflict of interest

None.

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Evaluation of quality of life and neuropathic pain in patients with low back pain using the Japanese Orthopedic Association Back Pain Evaluation Questionnaire.

To examine the impact that neuropathic or nociceptive pain has on the quality of life (QOL) in patients with low back pain (LBP) using the Japanese Or...
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