Differences between patients with fibromyalgia and chronic low back pain in balance and sensitivity to pain

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Title: Differences between patients with fibromyalgia and chronic low back pain in balance and sensitivity to pain

AUTHOR: Cynthia Noguera Carrión

Master’s Thesis

Master’s degree in Neuroscience

at the

UNIVERSITAT DE LES ILLES BALEARS Academic year 2015-2016

Date 09/09/2016

UIB Master’s Thesis Supervisor Pedro Montoya Jiménez

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1 INDEX

Abstract……….2

Introduction………...3

 Objective………6

Methods………..6

 Participants………6

 Assessment of physical function………..7

 Procedure………..10

 Statistical analyses………10

Results………10

Discussion………..23

Conclusions………26

References……….28

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2 ABSTRACT. Fibromyalgia and chronic low back pain are two chronic diseases with several similarities from a clinical point of view. Thus, for instance, both are high- frequent reasons for medical consultation in primary care and both seriously affect patient’s quality of life due to the numerous symptoms. Moreover, it has been observed that patients with fibromyalgia and chronic low back pain showed similar patterns in terms of the pain response. The objective of the present study was to analyse if patients with fibromyalgia and patients with chronic low back pain (CLBP) displayed a similar impairment of physical function or not. For this purpose, measurements of pain sensitivity, postural balance, muscle strength, fatigue and impact of pain on daily life was obtained by using objective standardized instruments and self-report questionnaires. Overall, we found that patients with fibromyalgia displayed worse performance in several motor tasks and reported greater impact of pain on daily life than patients with CLBP. Moreover, higher pain sensitivity at several body locations patients, together with reduced sensitivity to vibration stimuli were observed in patients with fibromyalgia in comparison with patients with CLBP. The present study suggests that in addition to the role of central sensitization for the maintenance of persistent pain, widespread brain changes could be also responsible for altered physical functioning and impaired quality of life in fibromyalgia in comparison with patients with chronic low back pain. This would imply that intervention techniques for pain relief should also include strategies for improving physical functioning in fibromyalgia.

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3 Introduction

Pain was scientifically defined in the early twentieth century as the psychical adjunct to an imperative protective reflex (Sherrington, 1900). This is a concise definition, and it underlines the urgent primitive dimension of pain, the motor response that is teleologically oriented to remove tissue from potentially damaging insults (Lamont et al; 2000). More recently, the focus has expanded to encompass the subjective emotional and motivational-affective components of pain. The international Association for the Study of Pain has proposed the following definition: Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Thus, even though traditionally viewed as an entirely sensory phenomenon, pain differs fundamentally from other conventional sensory modalities in that numerous and diverse types of stimuli are capable of initiating a complex multifaceted pain response (Hooten et al; 2013).

In contrast to acute pain, which is directly associated with body injury, chronic pain has been defined as a sensation without biological value that has persisted beyond the normal time and despite the usual customary efforts to diagnose and treat the original condition and injury. In addition, it has been noted that if pain persisted for six weeks (or longer than the anticipated healing time), a thorough assessment for the development of chronic pain is warranted. Previous research has also referred to chronic pain syndrome as the end of the spectrum of pain experience (Croft et al; 1996; Lamont et al;

2000; Staud & Rodriguez, 2006) and has been defined as a constellation of behaviours and cognitions associated with the significant life disruption that represents the persistence of pain (Bonica, 1990; Wassem et al; 2002; Moore et al; 2010; Low &

Schweinhardt, 2011).

Nowadays, chronic pain seems to affect at least 100 million of adults per year in America (Simon, 2012) and more than 6 million in Spain (Langley et al; 2011).

Prevalence in primary care settings ranges from 5 to 33% and often imposes upon clinicians the responsibility of managing a substantial disability that can be exacerbated by patient's distress. Due to its prevalence, the cost of chronic pain is substantial (Turk, 2002; Raftery et al; 2011). Chronic pain has the ability to disable and significantly decrease the quality of life for the individual and his/her support systems (Viejo &

Huerta, 2000; Smith et al; 2001; Casals & Samper, 2004). The financial and personal

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4 costs for those who are affected by chronic pain are also highly significant (Reid et al;

2002). Hence, the assessment of chronic pain should include determining the mechanisms of pain through documentation of pain location, intensity, quality and onset/duration, as well as its psychosocial impact on individual´s functional ability and mental health (Hooten et al; 2013).

Fibromyalgia (FM) is a chronic condition causing pain, stiffness, and tenderness of the muscles, tendons, and joints (Wolfe et al; 2010). According with the EPISER study, prevalence of fibromyalgia in the Spanish population is around 2.73%, with 4.2% for females and 0.2% for male (Carmona, 2001). Moreover, fibromyalgia is considered the most common cause of chronic diffuse musculoskeletal pain (Valverde, 2000). The main reported symptoms are widespread pain, accompanied by myalgia at imprecise locations, long lasting and difficult to accurately define the beginning of the same (Wolfe et al; 2010). The pain is usually diffuse, deep, intense and difficult to describe in many occasions, and generally worsens with intense physical exercise, cold and emotional stress (Wassem et al; 2002; Younger & Mackey, 2009; Miró et al, 2012).

These symptoms are accompanied by asthenia, fatigue and bad night's sleep or insomnia, reduced isometric strength in the lower extremities, bradykinesia, among others (Villanueva et al; 2004; Góes, 2010). Although the etiology is unknown and its pathophysiology is still controversial, one of the most promising approaches for understanding fibromyalgia focuses on the role of the (central) nervous system (CNS) (Staud et al, 2001). In this sense, several techniques have been applied to detect abnormalities in CNS function, such as functional neuroimaging, electrophysiological recordings, brain stimulation and examination of spinal fluids, and, in particular, quantitative sensory testing (QST) (Dadabhoy et al, 2008).

In contrast to fibromyalgia, chronic low back pain (CLBP) is a similar chronic pain condition but with known etiology and pathophysiology. CLBP symptoms range from a dull ache to a stabbing or shooting sensation. Usually, pain makes hard to move or to stand up (Castro et al; 2011). Acute back pain frequently starts suddenly, often after an injury from sports or heavy lifting (Casado, 2008), and it is considered chronic if lasts more than three months (Wisconsin, 2004). Concerning the etiology and pathophysiology, it is known that the lower back is an intricate structure of interconnected and overlapping elements (tendons, muscles and other soft tissues, nerve roots and highly sensitive nerves, small joints and complex and intervertebral discs with

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5 gelatinous cores) (Fleites & Álvarez, 1985; Castro et al; 2011). Thus, it is possible that irritation or problem in any of these structures may cause back pain or pain by radiating to other parts of the body (Samanta et al; 2003; Simmond, 2006). Pain caused by the resulting lower back muscle spasms can be strong and there are several syndromes that cause pain that can become chronic. Usually, traumatic injuries, secondary hyperlordosis to obesity, abdominal muscles flaccid or pregnancy, lumbar disc disease, infections, lumbosacral sacralization (decompensate overload, overweight or vicious posture), spondylolisthesis, spondyloarthrosis, scoliosis, tumours, inflammatory processes such as rheumatoid arthritis, ankylosing spondylitis, osteoporosis and arthrosis congenital or spinal stenosis are cited as causes of low back pain (Biyani, 2004). It has been suggested that a thorough interrogation, accompanied by a general physical examination of the painful area and the motor function should be conducted for the diagnosis of CLBP (Wisconsin, 2004).

Fibromyalgia and chronic low back pain are two chronic diseases with several similarities from a clinical point of view. Thus, for instance, both are high-frequent reasons for medical consultation in primary care (Andersson et al; 1999) and both seriously affect patient’s quality of life due to the numerous symptoms. Moreover, it has been observed that both patients with fibromyalgia and chronic low back pain showed enhanced pain sensitivity (hyperalgesia) in response to pain applied to a neutral site (thumbnail) in comparison with healthy controls (Giesecke et al, 2004). Furthermore fibromyalgia patients often report that their disease started with simple back pain (Lapossy et al, 1995; Müller et al; 2000) and thus chronic low back pain may be a pre- stage to fibromyalgia (Nijs & Van Houdenhove, 2009). In addition, movement dysfunction could be a co-morbid problem in these disorders, a cause or a consequence of pain. Some studies have suggested that pain may affect physical behaviour in some systematic ways (e.g., shorter-duration, slower, more fractionated movement) that are different from those characterizing other challenging conditions such as fatigue, regardless of the location, type, and chronicity of pain (Simmonds, 2006; Côté &

Bement, 2010). In addition, fibromyalgia and chronic low back pain have been associated with deficits in postural control, balance and a higher frequency of falls (Panjabi, 2003; Jones et al, 2011; Brumagne et al, 2008; Radebold et al, 2000).

Nevertheless, little is known about possible differences between patients with

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6 fibromyalgia and patients with chronic low back pain on physical function (including gait and balance) and quality of life.

The objective of the present study was to analyse the pain profile in fibromyalgia and chronic low back pain. To compare these pain profiles, this study assessed pain sensitivity, postural balance, muscle strength, fatigue and impact of pain on daily life by using subjective and objective measures. Considering that it has been suggested that fibromyalgia could cause a longstanding or permanent change in the function of the nociceptive nervous system (Gracely et al; 2002; Baraniuk, 2004; Nielsen &

Henriksson, 2007), it was hypothesised that patients with fibromyalgia would display more deficits in pain sensitivity, motor function and pain impact than patients with chronic low back pain.

Methods Participants

Thirty participants with fibromyalgia (FM) (n=15, 14 women) or chronic low back pain (CLBP) (n=15, 10 women) participated voluntarily in the study. Patients were excluded due to age below 30 or above 70 years old, pregnancy, neurological or psychiatric diseases (with exception of comorbid depression). All subjects were recruited from the Fibromyalgia Association of the Balearic Islands. Table 1 shows the sociodemographic

data for the two groups.

Table 1. Sociodemographic data

Group

FM CLBP

M SD M SD

Mean age 55.27 9.71 52.20 14.19

Weight 70.11 15.46 71.93 12.09

Height 159.53 6.81 167.67 7.51

Pain duration 9.53 8.123 12.67 9.34

BMI 27.71 6.83 25.71 4.71

Note: M = Mean; SD = Standard deviation

At the time of the study, most participants were taking pain medication such as analgesics, anxiolytics and antidepressants (Table 2).

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Table 2. Medication in fibromyalgia and chronic low back pain.

Group

FM CLBP

Analgesics Ibuprofen Paracetamol Metamizol

49 % 65 % 34 %

1 %

45 % 63 % 35%

2 % Anxiolytics

Diazepam Clonazepam Lorazepam

13 % 68 % 30 % 2 %

19 % 79 % 9 % 12%

Antidepressants Fluoxetina Citalopram

38 % 88 % 12 %

36 % 94 % 6 %

Interested participants were provided with a written explanation of the research objectives and the conditions under which various tests were performed. A signed an informed written consent was obtained if they agree to participate.

Assessment of physical function

Four types of measures about physical function were obtained: self-report questionnaires, motor function, balance and sensitivity.

Self-report questionnaires. The Fibromyalgia Impact Questionnaire (FIQ) is an extensively validated instrument designed to quantify the overall impact of fibromyalgia over many dimensions (e.g. function, pain level, fatigue, psychological distress, etc.).

The maximum test score is 100. The first 10 items evaluate the physical ability to perform tasks. Item 11 to 14 pain, items 15 and 16 fatigue, stiffness item 17, 18 anxiety and finally 19 depression. Thus, a higher score indicates a greater impact of the syndrome on the person (Monterde et al, 2004). The McGill pain questionnaire is a tool for the assessment of the impact of chronic pain on daily life. The short version has three subscales (A, B and C). Subscale A includes items that assess sensory function (items 1-11) and affective function (items 12-15). Subscale B consists of a visual

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8 analogue scale for assessing pain intensity. Finally, subscale C shows an evaluation scale of current pain intensity ranging from 0 (no pain) to 5 (unbearable pain) (Boyle et al; 2003).

Motor function tasks. The Berg Balance Scale is a performance-based assessment tool that was developed to measure standing balance during functional activities. It consists of 14 functional tasks (e.g., sitting unsupported, change of sitting to standing position or vice versa, standing with feet together, standing on one leg, turning 360 degrees) with scores ranging from 0 (cannot perform) to 4 (normal performance). Overall scores range from 0 (severely impaired balance) to 56 (excellent balance). Scores between 0 and 20 represent balance impairment, between 21 and 40 represent acceptable balance, and between 41 and 56 represent good balance. Scores lower than 46 are also considered as good predictors for the occurrence of multiple falls (Murir et al; 2008). This test is simple and easy to administer and it has been used for quantifying the role of balance in neurological disorders (Qutubuddin et al; 2005). The timed get up and go test (TUG) measures the time taken by an individual to stand up from a standard arm chair, walk a distance of 3 meters, turn, walk back to the chair, and sit down. Subjects were instructed to start the test with their back against the chair and to initiate the manoeuvres on the word “go”. They walked through the test once before being timed in order to become familiar with the test. A stopwatch was used to time the trial. Normal healthy elderly usually complete the task in 20 seconds or less (independent mobility). Values larger than 20 seconds indicate reduced mobility. Task performance correlates with gait speed, balance, functional level and ability to go out (Podsiadlo & Richardson, 1991;

Shumway-Cook et al; 2000). The six-minute walking test (6MWT) is a functional walking test in which the distance that a patient can walk within six minutes is evaluated. Subjects were instructed to walk for 6 minutes, with appropriate walking shoes, in order to measure the total distance walked. Two cones are placed with a distance of 20 meters between each and the subject must walk during those minutes going from cone to cone (Butland et al; 1982; Gochicoa-Rangel et al; 2015). The 6MWT is considered a good indicator of exercise tolerance and aerobic capacity, since it causes a physiological stress that does not demand the maximum aerobic capacity of a subject (Enright, 2003). The Borg scale is a self-report measure of fatigue and subjective perception of dyspnea (Burkhalter, 1996; Martínez-Moragón et al, 2003). It consists of a 10-point scale ranging from 0 (complete lack of dyspnea or fatigue) to 10

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9 (maximum dyspnea or fatigue). In the present study, ratings were obtained before and after the 6MWT. In addition, heart rate and blood pressure were measured before and after the 6MWT.

Static balance. Balance was assessed by using a modified version of the Romberg’s balance test (Khasnis & Gokula, 2003). For this purpose, participants were asked to remain in orthostatic position with their feet in parallel and separated, arms extended along the body and with eyes closed during one minute. The test is based on the fact that balance comes from the combination of several neurological systems (proprioception, vestibular input, and vision) and that maintaining balance while standing in the stationary position with closed eyes should rely on intact sensorimotor integration centers and motor pathways. Thus, the essential feature of the test is that the patient should become more unsteady with eyes closed. In the present study, we analyzed the oscillatory body movements during the test performance. Motion on the frontal and sagittal planes was captured with a digital video camera at 30 frames per second. The subject must carry on the head a diode that had two points to further analyze the motion parameters (velocity, acceleration and trajectory).

For analyses of motion parameters, a free open source software for computer vision analysis of human movement – CVMob - was used (CVMob, 2011). This program determines the displacement, velocity and acceleration in a movie by using computer vision techniques. Previous research has demonstrated that the software was very accurate for measuring position and velocity of human movement recorded by conventional cameras.

Sensitivity measures. Pressure pain sensitivity was assessed by using an algometer (Kinser et al; 2009). In the present study, pain pressure was bilaterally assessed at five body locations: epicondyle, ventral side of second metacarpal, greater trochanter, index fingertip and posterior superior iliac spine (PSIS). The strength of the lower extremities was assessed by using a dynamometer (Takei Physical Fitness Test). The subject was placed on top of the platform and was instructed to force upward, trying to put the body as vertical as possible (Olivares et al; 2014). Finally, peripheral sensory function was evaluated by using a Vibratron (Physitemp Instruments, Clifton, USA) (Deng et al;

1993). The Vibraton 2 consists of a controller and two identical transducers that were used to determine the intensity of the vibratory stimulus perceived by the patient. The

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10 testing started with a vibration intensity above the threshold (easily detected by the patient), and then it was gradually reduced, asking participants to indicate when the vibration was not perceived. The amplitude of vibration was measured in "vibration units" displayed on the control unit (Arezzo et al; 1985; Frenette et al; 1990).

Procedure

The assessment session was performed in a spacious and silent room (14 m x 12 m) by two investigators. After informed consent was signed, participants first completed the self-report questionnaires, followed by the motor function and sensitivity tasks. Finally, the static balance task was performed and recorded by using a video camera. The whole session lasted about one hour.

Statistical analyses

Statistical analyses were performed by using the SPSS software. Kolmogorov-Smirnov tests were previously carried out to test the normality assumption of the dependent variables. Mean comparisons between patients with fibromyalgia and chronic back pain were analyzed by using Student t-tests. In addition, Cohen's d was also calculated for determining the effect size. A size value less than 0.20 was considered nonsignificant, values between 0.20 and less than 0.50 were small, between 0.50 and less than 0.80 were moderate and equal to or greater than 0.80 were high.

Results

The Kolmogorov-Smirnov tests indicated that all dependent variables fulfilled the normality assumption for parametric analyses. Regarding the sociodemographic variables, significant group differences were only observed in height (t (28) = 3.107, p = .004), indicating that CLBP patients were higher than patients with fibromyalgia.

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Figure 1. FIQ Total Figure 2. FIQ Pain

Self-report questionnaires (FIQ and McGill pain questionnaire)

Significant group differences were found in the total scores of the FIQ (t (28) = 3.918, p

= .001) (d = 1.43) (Fig. 1), as well as in the FIQ sub-scales pain (t (28) = 2.859, p = .008) (d = 1.04) (Fig. 2), fatigue (t (28) = 3.648, p = .001) (d = 1.33) (Fig. 3), anxiety (t (28) = 3.970, p < .001) (d = 1.45) (Fig. 4), and depression (t (28) = 4.549, p < .001) (d = 1.66) (Fig. 5). In all cases, patients with fibromyalgia reported higher scores than patients with CLBP, indicating a worse impact of chronic pain on daily life. No significant group differences were in the FIQ sub-scales ability to perform tasks (t (19)

= 1.382, p = .182) (d = 0.50), and stiffness (t (28) = 1.907, p = .067) (d = 0.70).

Fibromyalgia Fibromyalgia

Chronic Low Back Pain

** **

Fibromyalgia

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Figure 3. FIQ Fatigue Figure 4. FIQ Anxiety

Figure 5. FIQ Depression

Regarding the McGill Pain questionnaire, significant group differences were observed in all three sub-scales (A, B, C). Thus, patients with fibromyalgia reported higher scores than patients with CLBP in the sensory (t (26) = 3.677, p = .001) (d = 1.34) (Fig. 7) and the affective components of pain (sub-scale A) (t (28) = 2.472, p = .020) (d = 0.90) (Fig.

8). Pain intensity as measured by the visual analogue scale of the McGill questionnaire (sub-scale B) was also higher in patients with fibromyalgia than patients with CLBP (t (28) = 2.316, p = .028) (d = 0.85) (Fig. 9). Finally, patients with fibromyalgia reported higher scores in the evaluative scale of the McGill questionnaire (sub-scale C) than patients with CLBP (t (28) = 3.400, p = .002) (d = 1.24) (Fig. 10). Again, higher scores in all these subscales indicated greater pain impact.

***

**

Fibromyalgia

Chronic Low Back Pain Chronic Low Back Pain

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13

Figure 6. McGill A Figure 7. McGill A sensoryscale

Figure 8. McGill A affective scale

Fibromyalgia

** **

*

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14 Figure 9. McGill B analogue visual scale Figure 10. McGill C evaluative

scale

Motor function tasks: Berg Balance Scale, TUG, 6MWT, and Borg scale

In general, patients with fibromyalgia performed worse than patients with CLBP in all measures of motor function. Thus, for instance, significant group differences were found in performance scores of the Berg Balance Scale (t (28) = 3.309, p = .003) (d = 1.21) (Fig. 11), indicating a worse performance in patients with fibromyalgia than in patients with CLBP. Moreover, although both groups of patients performed the TUG task in less than 20 seconds (criteria value for healthy performance in this test), patients with fibromyalgia were significantly slower than patients with CLBP (t (28) = 2.085, p

= 0.046) (d = 0.76) (Fig. 12). In a similar way, statistical analyses of the 6MWT revealed that patients with fibromyalgia walked less distance in 6 minutes than patients with CLBP (t (28) = 3.408, p = 0.002) (d = 1.24) (Fig. 13). Finally, analyses of physical effort obtained from the Borg scale revealed significant group differences in fatigue after (t (28) = 3.175), p = 0.004) (d = 1.16) (Fig. 15) and dyspnea before motor performance (t (28) = 2.165, p = 0.039) (d = 0.79) (Fig. 14), but not in dyspnea after (t

Fibromyalgia

* **

Fibromyalgia Chronic Low Fibromyalgia

Back Pain

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15 Figure 11. Berg Balance Scale

Figure 12. Timed get up and go test (TUG)

(28) = 1.736, p = 0.094) (d = 0.63) or fatigue before motor performance (t (28) = 1.970, p = 0.059) (d = 0.72).

**

Fibromyalgia Chronic Low

Back Pain

Fibromyalgia

**

Back Pain

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16 Sensitivity measures

Pain sensitivity obtained by algometry indicated that patients with fibromyalgia were more sensitive at different body locations than patients with CLBP (see Table 9). To the right epicondyle (t (28) = 2.723, p = 0.011) (d = 0.99) (Fig. 16); left epicondyle (t (28) = 2.507, p = 0.018) (d = 0.92) (Fig. 17); right second metacarpal ventral side (t (28) = 2.166, p = .039) (d = 0.79) (Fig. 18); right greater trochanter (t (22) = 2.863, p = .009) (d = 1.05) (Fig. 19); left greater trochanter (t (20) = 2.453, p = .023) (F = 6.388, p =

Figure 13. Six minute walking test (6MWT)

**

Back Pain

Fibromyalgia

* **

Back Pain

Chronic Low Back Pain Figure 14. Borg dyspnea before Figure 15. Borg fatigue after

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17 .017) (d = 0.90) (Fig. 20), right PSIS (t (21) = 2.607, p = .016) (F = 4.776, p = .037) (d

= 0.95) (Fig. 21), left PSIS (t (19) = 2.945, p = .008) (F = 4.874, p = .036) (d = 1.08) (Fig. 22).

No statistically significant differences for the second metacarpal left ventral (t (28) = 1.745, p = .092) (d = 0.63), the right index fingertip (t (28) = 1.981, p =. 57) (d = 0.72) and left index fingertip (t (28) = 1.511, p = 0.142) (d = 0.55). Similarly, results from the dynamometer test revealed that strength in the lower limbs was more reduced in patients with fibromyalgia than in patients with CLBP (t (18) = 4.555, p < 0.001) (d = 1.66) (Fig. 23). Finally, significant group differences were found vibration thresholds at all four body locations: right index (t (21) = 3.029, p = 0.006) (d = 1.11) (Fig. 24), left index (t (21) = 3.162, p = .005) (d = 1.15) (Fig. 25), right foot (t (23) = 2.954, p = .007) (d = 1.08) (Fig. 26), and left foot (t (24) = 3.374, p = .002) (d = 1.23) (Fig. 27). These results indicated that patients with fibromyalgia were less sensitive to vibration stimuli than patients with CLBP.

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18 Figure 17. Left Epicondyle

Fibromyalgia

*

* *

Figure 16. Right Epicondyle

Figure 18. Right second metacarpal ventral side

Figure 16. Right Epicondyle

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19 Figure 19. Right greater trochanter

Fibromyalgia

Chronic Low

Back Pain Chronic Low

Back Pain

** *

* **

Figure 20. Left greater trochanter

Figure 21. Right PSIS Figure 22. Left PSIS

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20 Figure 23. Dynamometer

Back Pain

***

Fibromyalgia

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21

Chronic Low Back Pain Figure 24. Right index threshold Figure 25. Left index threshold

Figure 26. Right foot threshold Figure 27. Left foot threshold Fibromyalgia

Fibromyalgia

Chronic Low

Back Pain Chronic Low

Back Pain

** **

Fibromyalgia

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22 Figure 28. Acceleration vector module

Figure 29. Trajectory Figure 30. Axis Y (Vertical)

Static Balance

Three parameters were obtained from the analyses of the Romberg’s static balance task:

velocity, acceleration and trajectory of the body sway. Significant group differences were observed in the acceleration vector module (t (15) = 2.144, p = .048) (d = 0.78) (Fig. 28), indicating that acceleration of body sway was greater in patients with fibromyalgia than in patients with CLBP. Moreover, it was also found that trajectory of body sway in the vertical plane was higher in patients with fibromyalgia than in patients with CLBP (t (28) = 2.618, p = .014) (d = 0.96) (Fig. 30). No significant group differences were observed in the velocity of body sways (t (18) = 2.055, p = 0.055) (d = 0.75) or the trajectory of the body sway in the horizontal plane (t (28) = .874, p = 0.389) (d = 0.32).

Fibromyalgia Chronic Low Back Pain

*

Fibromyalgia

Back Pain

* *

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23 Physiological measures

No significant group differences were observed in heart rate before (t (28) = .467, p = .644) (d = 0.17) or after the 6 minute walking test (t (28) = 1.854, p = .074) (d = 0.68).

No significant group differences were observed in blood pressure before (systolic: t (28)

= 1.239, p = .226; d = 0.45) (diastolic: t (17) = .660, p = .518; d = 0.24) or after the 6 minute walking test (systolic: t (28) = 1.456, p = .157; d = 0.53) (diastolic: t (28) = .538, p = .598; d = 0.20).

Discussion

The objective of the present study was to analyse if patients with fibromyalgia and patients with chronic low back pain (CLBP) displayed a similar impairment of physical function or not. For this purpose, measurements of pain sensitivity, postural balance, muscle strength, fatigue and impact of pain on daily life was obtained by using objective standardized instruments and self-report questionnaires. Based on previous evidence indicating that fibromyalgia could be considered a chronic disease with a major impact on the functioning of the nociceptive brain system (Baraniuk, 2004;

Nielsen, 2007; Latremoliere & Woolf, 2009), it was hypothesised that motor function would be more impaired in these patients than in those with CLBP. Overall, we found that patients with fibromyalgia displayed worse performance in several motor tasks and reported greater impact of pain on daily life than patients with CLBP. Moreover, higher pain sensitivity at several body locations patients, together with reduced sensitivity to vibration stimuli were observed in patients with fibromyalgia in comparison with patients with CLBP. Interestingly, all these group differences appeared in spite of similar intensity of clinical pain, pain duration or age in patients with fibromyalgia and patients with CLBP.

Self-report pain questionnaires such as the FIQ and the McGill makes possible to assess the impact of pain on quality of life. In the present study, we observed that patients with fibromyalgia reported more depression, anxiety and negative mood than patients with CLBP. Moreover, significant group differences were observed in all three sub-scales of McGill questionnaire (A, B, C). Patients with fibromyalgia reported higher scores than

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24 patients with CLBP in the sensory and affective components of pain. Pain intensity as measured by the visual analogue scale of the McGill questionnaire (sub-scale B) was also higher in patients with fibromyalgia than patients with CLBP. Finally, patients with fibromyalgia reported higher scores in the evaluative scale of the McGill questionnaire (sub-scale C) than patients with CLBP. This is consistent with data from other investigations showing elevated scores on alexithymia, somatization, depression, anxiety in fibromyalgia patients, this suggest that chronic pain patients might be particularly vulnerable to the effects of negative mood during information processing (Sitges et al; 2007;Tuzer et al; 2011, Cedraschi et al; 2012).

The assessment of motor function further showed that patients with fibromyalgia were also more impaired than patients with CLBP. Thus, for instance, patients with fibromyalgia were slower in the TUG and the 6-minute walking test (6MWT) and perceived greater fatigue than patients with CLBP, although there were no differences in clinical pain, pain duration, body-mass index or age between groups. Previous research has indicated that these tests are useful to determine the risk of falls (Shumway-Cook, 2000; Steffen, 2002), and performance could be related to pain sensitivity (Brown, 2007; Carbonell-Baeza, 2013). Moreover, research has shown that fatigue in fibromyalgia could be severe enough to limit patients’ motor activities and may lead to a sedentary lifestyle reducing physical abilities and increasing risk for disabilities (Bennett, et al; 2007). Nevertheless, current data on levels of physical function are mostly provided by community studies using subjective self-report measures (Da Costa et al; 2000). The present study expands previous results demonstrating that risk of falls in fibromyalgia could be associated with objective changes in motor function.

The kinematic parameters obtained from the modified version of the Romberg’s balance test also indicated that fibromyalgia patients displayed more impaired balance than healthy controls. Oscillatory movements on the frontal and sagittal planes and parameters of velocity and acceleration there were generally greater in fibromyalgia.

This finding is in accordance with a previous research suggesting that patients with fibromyalgia may also display balance deficits (Russek and Fulk, 2009). Taking into account that balance or postural stability is a complex task that involves the rapid and dynamic integration of multiple sensory, motor, and cognitive inputs to execute

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25 appropriate neuromuscular activity, it could be that patients with fibromyalgia may show significant alterations in these mechanisms (Horak, 2006).

Indeed, the findings of the present study are in agreement with previous studies showing that fibromyalgia may affect peripheral and/or central mechanisms of postural control (Jones et al; 2009). In this sense, previous research has proposed that muscle activation and recruitment could be altered in the presence of pain (neuromuscular activation model) (Sterling, 2001). According with this model, pain would affect the ability of muscles to perform synergistic functions related to maintaining joint stability and control. In this sense, a survey of 2,596 persons with FM reported balance problems as one of the top 10 most debilitating symptoms with a reported prevalence of 45%

(Bennet et al; 2007). Moreover, brain stimulation studies using transcranial magnetic stimulation (TMS) of the motor cortex demonstrated significant changes in cortical excitability and intracortical modulation in fibromyalgia (Salerno et al; 2000; Mhalla et al, 2010). These findings are also in agreement with a huge of accumulated evidence supporting the idea that chronic pain, such as it occurs in fibromyalgia, could be maintained due to significant alterations of brain functioning. In particular, central sensitization has been discussed as a key concept for the maintenance of chronic pain, leading to pain hypersensitivity, dynamic tactile allodynia and pressure hyperalgesia (Woolf, 2011). This phenomenon has been repeatedly confirmed in the case of fibromyalgia (Julien et al; 2005; Nielsen, 2007). Thus, it seems that patients with fibromyalgia could be characterized not only by an altered functioning of the somatosensory system, but also by a dysfunction of motor cortex involving excitatory and inhibitory mechanisms. This hypothesis would also explain the fact that worse motor performance in gait and balance tasks in fibromyalgia could be associated with increased number of falls (Berg, 1992; Lajoie, 2004).

Measurement of lower extremity strength, pain thresholds and sensitivity to vibration further supported the existence of significant alterations in somatosensory and motor mechanisms for postural control in patients with fibromyalgia as compared to patients with chronic low back pain. Our findings of enhanced pain sensitivity in fibromyalgia are in accordance with recent research, demonstrating that these patients displayed more pain sensitivity than patients with CLBP (Gerhardt & Blumenstiel, 2015). These data may suggest the existence of global central disinhibition as a potential mechanism in fibromyalgia, whereas a more localized alteration within the affected segment possibly

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26 due to peripheral sensitization would be more relevant in chronic low back pain. This would imply that fibromyalgia is the consequence of modified stimulus processing by the CNS without recognizable peripheral sources of nociceptive input or peripheral nerve dysfunction (Coderre et al; 1993, Desmeules et al; 2003). According with this interpretation, functional neuroimaging studies have consistently revealed that painful thermal, electrical, chemical, and pressure stimuli in fibromyalgia usually result in increased regional cerebral blood flow (rCBF) in structures involved in the processing of sensation, movement, cognition, and emotion (Jones et al 1991; Casey 1996; Peyron, 2000; Gracely et al 2002). Moreover, further studies have observed that central nervous system opioid dysfunction may contribute to pain in fibromyalgia but not in chronic low back pain (Baraniuk, 2004; Julien et al; 2005).

In summary, our data were consistent with the idea of worse physical function in fibromyalgia when compared to other chronic pain syndromes, such as CLBP.

Nevertheless, following shortcomings should be born in mind when interpreting the results. The sample size of the present study was small and the group distribution by sex was unequal. It could be also possible that physiological variables affecting pain perception such as blood pressure and heart rate would be more relevant in larger samples. It should be also noted that patients with chronic pain (fibromyalgia and CLBP) usually report sleep alterations (Smith, 2004) that could be influencing our results. Additionally, many of the medications used by these patients are associated with side effects of postural stability. Thus, for example, opioids, tricyclics, hypnotics, benzodiazepines, and cardiac medications can be associated with falls in the elderly (Jones et al, 2011). Therefore, this variable should be better controlled in future studies.

Finally, kinematic parameters of the gait cycle should be also analyzed since there are significant alterations in these parameters that could explain the reduced gait velocity in patients with fibromyalgia (Jiménez et al; 2009).

Conclusions

Our data revealed that patients with fibromyalgia had a more negative pain impact than patients with chronic low back pain. This was demonstrated by using subjective self- report questionnaires and objective measures of the motor function and balance, together with measurements of pain sensitivity, lower extremity strength and sensitivity

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27 to vibration stimuli. A plausible neurophysiological mechanism involved in the maintenance of chronic pain is central sensitization, which has been defined as an augmentation of responsiveness of central pain-signalling neurons to input from low- threshold mechanoreceptors (Staud et al, 2001). In this sense, central sensitization encompasses altered brain processing of sensory information and malfunctioning of pain-inhibitory brain mechanisms, involving multiple brain sites such as sensory (thalamus, insula, primary and secondary somatosensory cortices), cognitive evaluative- affective (anterior cingulated cortex and prefrontal cortex), and pain-modulating regions (anterior cingulated cortex and periaqueductal gray matter) (Staud et al., 2007). Thus, it seems that central sensitization is characterized by an enhanced reactivity of pain- related brain regions, as well as by a malfunctioning of central pain-inhibitory pathways. This appears particularly relevant given that both isometric and aerobic exercises activate endogenous opioid and adrenergic pain-inhibitory mechanisms in healthy subjects, but increases experimental pain ratings in patients with fibromyalgia (Staud et al., 2005) and chronic fatigue syndrome (Whiteside et al., 2004). Further studies are necessary to identify the relative contribution of neural, muscular and anthropomorphic challenges to postural stability in patients with fibromyalgia and chronic back pain and develop specific balance interventions to remediate these impairments. Finally, the present study shows that chronic pain syndromes can also have a considerable impact on daily activities and quality of life. It is therefore necessary that investigations are directed to try to reduce the negative impact generated by these pathologies in different areas, with appropriate therapy could achieve improved patient and above all a better quality of life.

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