Clin Rheumatol (2008) 27:1543–1547 DOI 10.1007/s10067-008-0966-1

ORIGINAL ARTICLE

A cross-sectional study of the relationship between body mass index and clinical characteristics, tenderness measures, quality of life, and physical functioning in fibromyalgia patients Lily Neumann & Ella Lerner & Yael Glazer & Arkady Bolotin & Alexander Shefer & Dan Buskila

Received: 15 October 2007 / Revised: 10 June 2008 / Accepted: 25 June 2008 / Published online: 12 July 2008 # Clinical Rheumatology 2008

Abstract We examined the relationship between body mass index (BMI) and measures of tenderness, quality of life, and physical functioning in female fibromyalgia (FMS) patients. A random sample of 100 female FMS patients from a database of 550 FMS individuals was interviewed and assessed according to a structured questionnaire that included FMS-related symptoms, measures of tenderness (point count and dolorimetry), quality of life (SF-36), physical functioning, and BMI. Weight was defined as normal, overweight, and obesity according to BMI. Twenty-seven percent of the FMS patients had normal BMI, 28% were overweight, and 45% were obese. BMI was negatively correlated with quality of life (r=−0.205, P=0.044) and tenderness threshold (r=−0.238, P=0.021) and positively correlated with physical dysfunctioning (r= 0.202, P=0.047) and point count (r=0.261, P=0.011). Obese FMS patients display higher pain sensitivity and lower levels of quality of life. In designing studies that explore factors affecting tenderness, BMI should be included in addition to sex, age, etc. Keywords Body mass index . Fibromyalgia . Obesity . Pain . Physical functioning . Quality of life L. Neumann (*) : Y. Glazer : A. Bolotin Epidemiology Department, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel e-mail: [email protected] E. Lerner : A. Shefer : D. Buskila Internal Medicine, Soroka Medical Center and Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel

Fibromyalgia syndrome (FMS) is characterized by widespread pain and various associated symptoms as well as increased pain sensitivity and higher nonarticular tenderness to different pain stimuli. Studies have demonstrated the existence of several factors affecting tenderness, namely, gender, age, diagnosis, ethnicity, and educational level [1–4]. The relationship between obesity and nonarticular tenderness has scarcely been studied, though in National Institute of Health conference in 1994 on fibromyalgia, it was recommended that this issue should be studied [5]. We have previously reported that obese women display increased nonarticular tenderness [6]. Interestingly, this tenderness remained high after weight reduction following bariatric surgery [7]. Data on the relationship between body mass index (BMI) and chronic pain are also limited. In a study that assessed blood pressure and metabolic factors in relation to chronic pain, it was found that subjects with widespread pain and/or intense chronic pain had higher BMI than healthy controls [8]. Yunus et al. [9] provided the first report examining the relationship between FMS and BMI. Two hundred eleven female FMS patients were analyzed, and a significant positive correlation was found between BMI and age and a negative correlation between BMI and educational level. Health assessment questionnaire (HAQ) score was significantly correlated with BMI, whereas fatigue and number of tender points showed a trend [9]. Consistent with the study of Yunus et al. [9], it was reported that in FMS patients, weight was positively correlated with multiple pain measures, functional disability, and pain interference [10]. In addition, pain was positively correlated with depression, anxiety, and body concerns and negatively related to quality of life (QoL). In

1544

this study, weight loss significantly predicted a reduction in FMS-related symptoms and improvement in QoL [10]. The aim of the present study was to further examine the relationship between BMI and FMS-related symptoms, measures of tenderness, quality of life, and physical functioning in female FMS patients.

Materials and methods Subjects The 100 subjects were randomly chosen from a list of 550 female patients with FMS attending the rheumatology outpatients’ clinic in the Soroka University Hospital, Beer Sheva, Israel. The clinic serves as a tertiary referral center for the southern part of Israel. All subjects fulfilled the 1990 American College of Rheumatology criteria for the classification of FMS [11]. All data were collected by protocol, which included demographic and clinical background, assessment of quality of life, physical functioning, and measures of tenderness (point count and dolorimetry). Each patient was assessed by the same researcher (EL). Body mass index was calculated as weight in kilograms divided by the square of the height in meters. Normal weight was defined as BMI 18.5–24.9, overweight as BMI 25.0–29.0, and obesity as BMI≥30. The study was approved by the Helsinki Ethics’ Committee of the Soroka Medical Center, with all participants giving their written consent after having received detailed information about the study. FMS symptoms Visual analog scales were used by the subjects to evaluate their current level of pain, fatigue, anxiety, depression, morning stiffness, and the global well-being. The items were scored on a 0- to 10-point scale, with 10 denoting the worst possible condition. The reported frequencies of headache, paresthesias, sleep disturbances, subjective joint swelling, and irritable bowel syndrome were also recorded. Physical functioning assessment Physical functioning was assessed using the Fibromyalgia Impact Questionnaire (FIQ) [12, 13]. The first part of the FIQ focuses on the patients’ ability to perform daily tasks (i.e., cooking, cleaning, walking, etc.) and contains ten items with responses ranked 0 to 3, where 0=always able to do, and 3=never able to do. The mean of these items yields one physical functioning score.

Clin Rheumatol (2008) 27:1543–1547

Quality of life assessment Quality of life was assessed by SF-36 [14, 15]. This is a health-related profile of QoL that contains 36 items and measures health status across three domains: functional status, well-being, and overall evaluation of health. Its psychometric properties are well characterized, and it has been determined to have high reliability and validity in a wide range of patient populations [16], including rheumatologic conditions [17, 18]. The Hebrew translation of the SF-36 was validated in the adult general population [19], and we used it in patients with widespread pain [20]. The SF-36 contains eight scales: physical functioning, social functioning, and role limitations attributable to physical and emotional problems, mental health, vitality, bodily pain, and general health. Each scale generates a score from 0 to 100, with a higher score indicating better health and less body pain. Tenderness assessment Tenderness was assessed manually and with a dolirimeter at tender points and control sites [11]. Tender points are specific, predictable autonomic sites that reveal tenderness upon physical examination that is lacking in control sites. A count of 18 tender points in nine symmetric sites was performed by thumb palpation. Manual pressure was demonstrated at control site first. Subjects were told to expect sensation of pressure but to indicate if it became painful. Definite tenderness at any of the points was considered to be present if some involuntary verbal or facial expression of pain occurred or wince or withdrawal was observed. The amount of manual pressure applied over the tender points was about 4 kg/cm2 (tested periodically with a dolorimeter).

Table 1 Severity and frequency of FMS-related symptoms Symptoms Severitya Pain Fatigue Anxiety Depression Morning stiffness Global well being Reported frequency Sleep disturbance Headache Paresthesias Subjective joint swelling Irritable bowel syndrome a

Mean (SD)

7.2 7.5 3.8 4.4 6.3 6.9

n

Percent

83 87 86 77 45

83 87 86 77 45

(2.8) (3.4) (3.6) (3.4) (2.3) (2.5)

The scale is 0–10, 10=worst condition

Clin Rheumatol (2008) 27:1543–1547

1545

Table 2 Correlation coefficients between BMI and measures of quality of life, physical functioning, and measures of tenderness Variable

BMI

Quality of lifea Physical dysfunctioningb Point count Tenderness thresholdc (at 9 tender points)

−0.205 0.202 0.261 −0.238

P value 0.044 0.047 0.011 0.021

a

From SF-36 From FIQ c Dolorimetry b

rate about 1 kg/s. The subject was asked to say yes when the sensation changed from the pressure to definite pain. Preliminary measurements of the control sites were obtained not only to familiarize the subject with the process but also to discourage anticipation of exaggerated responses. Patients were not told which were tender points and which were control points, and the points were mixed together in the examination. All dolorimeter measurements, as well as a total point count, were done by one observer. Statistical analysis

Thirteen point sites (nine tender point sites and four control sites) were further studied using a dolorimeter. The nine tender points were: the trapezius muscle (right and left), midpoint of the upper fold; the occiput (right), below the occipital prominence; cervical spine (right) the anterior aspects of the intertransverse spaces at C3–C5; the second costochondral junction (right) just lateral to the junctions, on the upper surface; the medial fat pad of the knee (right and left); 2 cm distal to the lateral epicondyle (right); and 2 cm posterior to the greater trochanter (right). The four control sites were: the forehead (middle), the forearm (right distal third); the lateral surface of the knee (right); and the shaft of the third metatarsal (right). The tenderness threshold was measured using Chatillon dolorimeter, model 719-20, which has a maximum scale of 10 kg, with neoprene stopper footplate with a diameter of 1.4 cm [21]. The site of maximal tenderness over tender points was determined by preliminary light pressure. The footplate of the dolorimeter was then placed appropriately, and if necessary, its location was stabilized with examiner’s nondominant hand to prevent (often painful) shifting of the footplate under pressure, with care being taken not to add or subtract from the force applied. The dolorimeter was held close to the vertical position. Pressure was increased at the

Spearman correlation coefficients were applied to assess relationships between continuous variables. The Kruskal– Wallis test (with Bonferroni correction) was used to compare measures of quality of life, physical functioning, and tenderness in three BMI categories.

Results The study population included 100 FMS women. Their average age was 53.5 years (±11.6), and their average BMI was 29.4 (±SD, 5.6). Twenty-seven percent had normal BMI, 28% were overweight, and 45% were obese. Sixtyeight percent were married, they had little formal education (10.9±SD, 4.5 years of education), and only 18% were employed. Table 1 indicates a high frequency and considerable severity of FMS-related symptoms in the sample. The subjects displayed a high pain sensitivity: their mean point count was 15.7 tender points (±SD, 2.3) and their mean tenderness threshold was 2.4 kg (±SD, 0.8). Significant correlations were observed between BMI and measures of quality of life, physical functioning, point count, and tenderness threshold (Table 2). BMI was

Table 3 Measures of quality of life, physical functioning, and tenderness by BMI categories (n=100) Variable Quality of life

Physical functioning

Point count

Tenderness threshold

a b

Range Median Mean (SD) Range Median Mean (SD) Range Median Mean (SD) Range Median Mean (SD)

Normal BMI (20–24.9)a n=27

Overweight (25–29.9)a n=28

Obesity (30.0+)a n=45

28.7–49.3 39.8 41.4(16.7) 0.2–2.9 1.1 1.2(0.8) 11.0–18.0 14.0 15.1(2.4) 1.1–4.0 2.7 2.6(0.8)

26.0–42.7 32.7 37.5(17.4) 0.1–2.7 1.9 1.6(0.8) 10.0–18.0 15.0 15.3(2.4) 1.2–4.0 2.8 2.6(0.8)

26.5–35.5 31.0 35.3(17.1) 0.0–2.8 1.8 1.7(0.9) 13.0–18.0 17.5 16.4(1.9) 1.0–3.6 2.0 2.2(0.8)

BMI limits Kruskal–Wallis test (with Bonferroni correction), α=0.017

P valueb 0.261

0.136

0.099

0.050

1546

negatively correlated with quality of life (r=−0.205, P= 0.044) and tenderness threshold (r=−0.238, P=0.021) and positively correlated with physical dysfunctioning (r= 0.202, P=0.047) and point count (r=0.261, P=0.011). A similar trend was observed when we compared the abovementioned measures in three categories of BMI: normal, overweight, and obese (Table 3).

Discussion The present study of FMS patients demonstrates that our FMS patients are overweight, and they have lower quality of life and have higher pain sensitivity compared with patients with normal weight. Our study confirmed prior findings reported by Yunus et al., where the HAQ score was negatively associated with BMI, and there was a positive trend in the correlation between BMI and fatigue. Data on the relationship between BMI and chronic pain are limited. Pradalier et al. [22] evaluated the relationship between pain and obesity in healthy pain-free women. They used an electrophysiological method to measure pain sensation and reported a correlation between nociceptive threshold and overweight [22]. Mckendall and Haier [23] reported that obese subjects were found to be significantly more pain sensitive than nonobese subjects. Nilsson et al. [8] found that subjects with widespread pain or intense chronic pain had higher BMI than healthy controls. Buskila et al. [6] assessed tenderness using point count of 18 tender points and dolorimetry thresholds in 54 obese women and 54 age-related women with normal weight. The obese women displayed significantly higher sensitivity to pain than the normal weight controls. In addition, the obese women reported significantly lower quality of life, and their tenderness was negatively correlated with quality of life [6]. In a subsequent study, we examined the effect of weight reduction on tenderness [7]. Forty-two obese women were evaluated for tenderness before and 6 months after bariatric surgery. We confirmed our previous observation that obese subjects display increased tenderness. However, the level of increased tenderness remained unchanged 6 months after the surgery. These findings are contradictory to those reported by Larsson [24]. He showed that weight reduction had a positive short-term effect on musculoskeletal pain. A recent study of FMS patients reported that although weight was not related to pain at baseline, weight loss significantly predicted a reduction in FMS-related symptoms, body satisfaction, and quality of life [10]. It was suggested that behavioral weight loss treatment could be included in the treatment of overweight-obese women with FMS. It is not clear why obese subjects have higher pain sensitivity; it may result from local or general factors. It is

Clin Rheumatol (2008) 27:1543–1547

possible that high subcutaneous fat results in higher pain sensitivity, and it may be hypothesized that there are more pain receptors in fat tissue. Furthermore, other types of pain such as visceral pain have been found increased in obesity. Gastrointestinal symptoms were found to be more intense in morbidly obese patients [25], and chronic abdominal wall pain was frequently associated with obesity [26]. General factors that predispose obese subjects to higher sensitivity may be associated with deconditioning as often is seen in FMS patients. It is possible that the difference in pain sensitivity between obese and nonobese subjects may be related to endogenous opiates, since they have been implicated as regulators of mood and pain [23]. Indeed, a defect in endogenous opiods system was suggested in obese Zucker rats [27]. The recognition of the association between obesity and increased tenderness is important to physicians taking care of obese individuals and FMS patients. Symptoms of increased tenderness in these subjects may be misinterpreted by the physician unfamiliar with these associations as part of an underlying disease. Furthermore, these observations are important for researches in the field of pain. In designing future studies that explore factors affecting tenderness, BMI should be included in addition to gender and other factors. Conflict of interest statement

None.

References 1. Buskila D, Langevitz P, Gladman DD, Urowitz S, Smythe HA (1992) Patients with rheumatoid arthritis are more tender than those with psoriatic arthritis. J Rheumatol 19:1115–1119 2. Buskila D, Neumann L, Press J, Zaks N, Gedalia A (1995) Assessment of nonarticular tenderness of children of different ethnic groups. J Musculoskeletal Pain 3:83–90 3. Buskila D, Gladman DD, Langevitz P, Urowitz S, Smythe HA (1990) Fibromyalgia in human immunodeficiency virus infection. J Rheumatol 17:1202–1206 4. Neumann L, Buskila D (1998) Ethnocultural and educational differences in Israeli women correlate with pain perception in fibromyalgia. J Rheumatol 25:1369–1373 5. Pillemer SR (1994) The fibromyalgia syndrome: current research and future directions in epidemiology pathogenesis and treatment. NIH conference. J Musculoskeletal Pain 2:113–115 6. Buskila D, Neumann L, Frenkel A, Bolotin A, Levi I, Press J (2002) Increased nonarticular tenderness in obese woman. Pain Clin 13:313–318 7. Buskila D, Neumann L, Malkin S, Levi I (2005) Does nonarticular tenderness change after bariatric surgery? Obes Surg 15:1243–1246 8. Nilsson PM, Kandell-Collen A, Andersson HI (1997) Blood pressure and metabolic factors in relation to chronic pain. Blood Press 6:294–298 9. Yunus MB, Arslan S, Aldag JC (2002) Relationship between body mass index and fibromyalgia features. Scand J Rheumatol 31:27–31

Clin Rheumatol (2008) 27:1543–1547 10. Shapiro JR, Anderson DA, Danoff-Burg S (2005) A pilot study of the effects of behavioral weight loss treatment on fibromyalgia symptoms. J Psychosom Res 59:275–282 11. Wolfe F, Smythe HA, Yunus MB, Bennett RM, Bombardier C, Goldenberg DL, Tugwell P, Campbell SM, Abeles M, Clark P et al (1990) The American College of Rheumatology 1990 Criteria for the classification of fibromyalgia. Report of the multicenter criteria committee. Arthritis Rheum 33:160–172 12. Burckhardt CS, Clark SR, Bennett RM (1991) The fibromyalgia impact questionnaire: development and validation. J Rheumatol 18:728–733 13. Buskila D, Neumann L (1996) Assessing functional disability and health status of women with fibromyalgia: validation of a Hebrew version of the Fibromyalgia Impact Questionnaire. J Rheumatol 23:903–906 14. Stewart AL, Hays RD, Ware JE (1988) The MOS short-form general health survey. Reliability and validity in a patient population. Med Care 26:724–735 15. Ware JE Jr, Snow KK, Kosinski M et al (1993) SF-36 Health survey: manual and interpretation guide. New England Medical Center, The Health Institute, Boston 16. McHorney CA, Ware JE Jr, Lu JF, Sherbourne CD (1994) The MOS 36-item short-form health survey (SF-36): III. Tests of data quality. Med Care 32:40–66 17. Gladman DD, Urowitz MB, Gough J, MacKinnon A (1997) Fibromyalgia is a major contributor to quality of life in lupus. J Rheumatol 24:2145–2148 18. Ruta DA, Hurst NP, Kind P, Hunter M, Stubbings A (1998) Measuring health status in British patients with rheumatoid arthritis: reliability, validity and responsiveness of the short form 36-item health survey (SF-36). Br J Rheumatol 37:425–436

1547 19. Lewin-Epstein N, Sagiv-Schifter T, Shabtai EL, Shmueli A (1998) Validation of the 36-item short-form Health Survey (Hebrew version) in the adult population of Israel. Med Care 36:1361–1370 20. Neumann L, Berzak A, Buskila D (2000) Measuring health status in Israeli patients with fibromyalgia syndrome and widespread pain and healthy individuals: utility of the short form 36-item health survey (SF-36). Semin Arthritis Rheum 29:400–408 21. McCarty DJ Jr, Gatter RA, Steele AD (1968) A twenty-pound dolorimeter for quantification of articular tenderness. Arthritis Rheum 11:696–698 22. Pradalier A, Willer JC, Boureau F, Dry J (1981) Relationship between pain and obesity: an electrophysiological study. Physiol Behav 27:961–964 23. McKendall MJ, Haier RJ (1983) Pain sensitivity and obesity. Psychiatry Res 8:119–125 24. Larsson UE (2004) Influence of weight loss on pain, perceived disability and observed functional limitations in obese women. Int J Obes Relat Metab Disord 28:269–277 25. Clements RH, Gonzales QH, Foster A et al (2003) Gastrointestinal symptoms are more intense in morbidly obese patients and are improved with laparoscopic Roux-en-Y gastric bypass. Obes Surg 13:610–614 26. Costanza CD, Longstreth GF, Liu AL (2004) Chronic abdominal wall pain: clinical features, health care costs, and long-term outcome. Clin Gastroenterol Hepatol 2:395–399 27. Roane DS, Porter JR (1986) Nociception and opioid-induced analgesia in lean (Fa/−) and obese (fa/fa) Zucker rats. Physiol Behav 38:215–218