Cerebrospinal fluid levels of opioid peptides in fibromyalgia and chronic low back pain
© Baraniuk et al; licensee BioMed Central Ltd. 2004
Received: 10 March 2004
Accepted: 09 December 2004
Published: 09 December 2004
The mechanism(s) of nociceptive dysfunction and potential roles of opioid neurotransmitters are unresolved in the chronic pain syndromes of fibromyalgia and chronic low back pain.
History and physical examinations, tender point examinations, and questionnaires were used to identify 14 fibromyalgia, 10 chronic low back pain and 6 normal control subjects. Lumbar punctures were performed. Met-enkephalin-Arg6-Phe7 (MEAP) and nociceptin immunoreactive materials were measured in the cerebrospinal fluid by radioimmunoassays.
Fibromyalgia (117.6 pg/ml; 85.9 to 149.4; mean, 95% C.I.; p = 0.009) and low back pain (92.3 pg/ml; 56.9 to 127.7; p = 0.049) groups had significantly higher MEAP than the normal control group (35.7 pg/ml; 15.0 to 56.5). MEAP was inversely correlated to systemic pain thresholds. Nociceptin was not different between groups. Systemic Complaints questionnaire responses were significantly ranked as fibromyalgia > back pain > normal. SF-36 domains demonstrated severe disability for the low back pain group, intermediate results in fibromyalgia, and high function in the normal group.
Fibromyalgia was distinguished by higher cerebrospinal fluid MEAP, systemic complaints, and manual tender points; intermediate SF-36 scores; and lower pain thresholds compared to the low back pain and normal groups. MEAP and systemic pain thresholds were inversely correlated in low back pain subjects. Central nervous system opioid dysfunction may contribute to pain in fibromyalgia.
Fibromyalgia (FM) is an enigmatic condition characterized by increased complaints of widespread pain with tenderness to palpation . The tenderness is traditional tested by manually pressing over so-called tender points, but more recent studies have shown that the tenderness is generalized phenomenon . The mechanisms responsible for the increase in the perception of pain in FM, and the variation of pain sensitivity in the general population are unclear. A similar continuum is seen with heat – induced pain. However, when subjects who report pain to a minimal stimulus (low pain threshold) were compared to subjects reporting less pain with the same stimulus (high pain threshold), there was enhanced functional magnetic resonance imaging (fMRI) responses in the low pain threshold group . The differences in activation were greatest in the primary somatosensory cortex, anterior cingulate cortex and prefrontal cortex. These fMRI patterns suggest there may be a continuum within the population for pain thresholds, central cortical activation and verbalized pain perception. These results may be applicable to FM since the same brain regions have been identified in response to painful stimuli .
The pain present in FM may induce antinociceptive neural mechanisms with the release of opioid peptides. This hypothesis was tested by measuring opioid peptides in cerebrospinal fluid, and comparing these levels to systemic pain thresholds, subjective complaints, and quality of life measures in 3 sets of volunteers. FM and Chronic Fatigue Syndrome often overlap . Chronic Fatigue Syndrome is characterized by severe fatigue associated with exertional exhaustion, pain symptoms, neurocognitive and sleep dysfunction . Therefore, opioid levels were compared for FM and FM/ Chronic Fatigue Syndrome subsets. The second group had chronic low back pain (LBP) without FM or Chronic Fatigue Syndrome. These subjects have a chronic regional pain syndrome  and served as a positive control group. The negative control group was formed by healthy persons with no pain or fatigue.
Two peptides were selected for measurements because they were involved in antinociceptive responses. Alternatively, dysfunction of their release could predispose to chronic pain. Preproenkephalin A is the precursor for leucine-enkephalin, methionine-enkephalin (Met-enk), Met-enk-Arg6-Gly7-Leu8, and Met-enk-Arg6-Phe7 (MEAP) . MEAP was elevated in many brain regions in inflammatory models of arthritis and gluteal carregeenan injection in rats [9, 10]. Nociceptin, also known as orphanin FQ, was increased in the cingulate gyrus in rat chronic pain models .
FM, LBP and Normal control subjects between the ages of 18 and 70 years were recruited to this IRB-approved protocol from rheumatology and orthopedics clinics, advertisements, and word of mouth. Normal subjects were pain and chronic fatigue free, had no diabetic, neurologic, inflammatory, autoimmune, or other chronic disorder that could predispose to pain, alterations in sensation, or known variations in cerebrospinal fluid composition. LBP inclusion criteria were (i) dominant pain complaint of low back pain, and (ii) imaging studies within the past 6 months. Exclusion criteria were: (a) evidence of a lumbar fracture or tumor to explain the pain, (b) any chronic illness that may affect functional status such as diabetes, cancer, chronic obstructive pulmonary disease, chronic inflammatory diseases, renal insufficiency or similar debilitating disorders, (c) previous back or neck surgery, and (d) FM or Chronic Fatigue Syndrome. FM subjects had a prior clinical diagnosis of FM including widespread pain affecting all 4 quadrants and the axial skeleton lasting at least 3 months that was not explained by any other chronic illness, and the presence of at least 11 of 18 tender points when manual, digital pressure of ~4 kg was applied . All subjects were medication-free for at least 4 days prior to study. Subjects participated in a 1/2 day protocol that involved confirmatory history and physical examination, questionnaires, tender point examinations, and lumbar puncture.
Systemic complaints questionnaire
This self – report questionnaire containing 44 queries grouped into the following modules: (i) Fatigue; (ii) Musculoskeletal: morning stiffness, muscle pain, muscle spasms, dry eyes, dry mouth, fingers sensitive to the cold, fingers turn blue and/or white in the cold, swollen lymph nodes, swollen joints, fever; (iii) Chest: shortness of breath (SOB), SOB when hurrying on level ground or walking up a slight hill, SOB when walking with other people of own age on level ground, stop for breath when walking at own pace on level ground, SOB when washing or dressing, rapid heart rate, chest pain, irregular heart rate, palpitations; (iv) Headaches: migraine or tension type; (v) Neurological: numbness or tingling of hands or legs, inability to concentrate, problems with memory, dizziness; (v) Ear, Nose and Throat (ENT): problems with balance, hearing loss, ear pain, sensation of ear blockage or fullness, ringing in the ears, sinus pain; (vi) Bladder: urinary urgency, pelvic discomfort / pain / pressure, persistent bladder fullness after urination, dysuria; and (vii) Irritable Bowel Syndrome (Rome I criteria): abdominal pain relieved with bowel movement, abdominal pain with a change in frequency or consistency of stool, changes in stool consistency, changes in stool form (hard or loose/watery), changes in passing of stool, bloating or feeling of abdominal distention, passage of mucus, nausea or vomiting . Subjects were asked to respond "Yes" if they had recurrent or chronic symptoms for more than 3 of the past 12 months. The sum of positive responses for each module and the total were determined.
Subjects completed the MOS SF-36. The domains were Physical Functioning (PF), Social Functioning (SF), Role Limitation due to Physical Problems (PP), Role Limitation due to Emotional Problems (EP), Mental Health (MH), Energy / Fatigue (E/F), Pain (P), General Perception of Health (GP) and Change in Health (CH).
Pain threshold and tender point examinations
All subjects had pressure testing at 9 bilateral sites (18 total) using a hand held dolorimeter (algometer) with a 1 cm2 rubber stopper making contact with the skin (Chatillon, etc.) [1, 2]. The degree of pressure required to cause pain (pain threshold) was recorded at each site, and the number with pain induced by < 4 kg / cm2 recorded. The average pressure causing pain was the Average Pain Threshold. FM and Normal subjects had manual digital pressure examinations of these points [1, 2]. The number of points that were painful was recorded as Manual Tender Points.
Cerebrospinal fluid (CSF) radioimmunoassays
Lumbar punctures were performed using local anesthetic and 23G spinal catheters. Volumes of 4 to 8 ml were obtained, centrifuged, aliquoted, and immediately frozen at -80°C. Samples were shipped on dry ice to Dr. Lars Terenius for measurement of neuropeptides. Neuropeptides were extracted from 1 ml aliquots using C-18 SepPak cartridges, eluted, dried, and resuspended for validated radioimmunoassays for MEAP [13, 14] and nociceptin  using the standard methodologies developed in their laboratory. Concentrations in samples were interpolated from parallel standard curves. There was insufficient CSF to use HPLC for precise peptide identification. Hence, immunoreactive materials (irm) were measured as MEAP-irm and nociceptin-irm.
Geometric mean and 95% confidence intervals were determined for each neuropeptide, with arithmetic means and 95% CI's for all other variables. Differences between groups were assessed by ANOVA. Differences between means for each pair of groups were assessed by 2-tailed unpaired Student's t-tests with Bonferroni corrections for multiple comparisons. Significance was ascribed for p < 0.05.
Lumbar punctures were performed on 14 FM (1 male), 10 LBP (5 male) and 6 Normal (2 male) subjects. The averages and ranges of ages for these 3 groups were similar (overall average 42.7 yr, 38.8 to 46.6; 95% CI). There were 4 African-Americans in the FM group, and 1 each in the LBP and Normal groups, and 1 Asian in the FM group. The remainder was Caucasian.
Systemic complaints questionnaire
Pain thresholds and tender point counts
Cerebrospinal fluid neuropeptide concentrations
MEAP – irm
Nociceptin – irm was not different between FM (4.27 pg/ml, 3.22 to 5.66, n = 14), LBP (4.52 pg/ml, 3.12 to 6.55, n = 10) and Normal (5.65 pg/ml, 2.65 to 12.04, n = 6) groups.
Systemic pain thresholds and MEAP – irm
The LBP group had a chronic regional pain syndrome, no fibromyalgia, normal pain thresholds and systemic complaints, but severe disability (SF-36 scores). Only the LBP group showed a linear correlation between pain threshold and MEAP – irm concentrations (figure 6). The parameters of this correlation were similar to that of the entire group. This was due to the overlap of some high pain threshold / low MEAP – irm LBP subjects with the Normal group, and low pain threshold / high MEAP – irm LBP subjects with the FM data. This continuum of pain threshold and MEAP – irm levels in LBP was different from the clustered FM and Normal datasets, and suggested a different mechanism of MEAP – irm regulation in LBP from FM.
The Normal group had Systemic Complaints and SF-36 scores in the normal ranges, high pain thresholds, low numbers of manual and dolorimetry-derived tender points, and low CSF concentrations of MEAP – irm and nociceptin – irm.
The LBP group was a positive control for chronic regional pain. Their Systemic Complaints scores, systemic pain thresholds and dolorimetry defined tender point counts were not significantly different from Normal. However, most of their SF-36 results were near zero indicating the worst level of impairment of the 3 groups. They were the only group to show a correlation of decreasing pain thresholds with increasing MEAP – irm concentrations. The continuum of MEAP – irm levels in the LBP group led to borderline significance for the comparison to Normal levels. Inclusion of LBP subjects with higher or lower pain thresholds may have shifted the MEAP – irm concentration distribution towards or away, respectively, from the Normal group results. This is important when comparing these data to those of other studies. For example, chronic sciatica patients did not have elevated MEAP – irm compared to controls . However, severity was not graded as extensively as in our study. Some subjects may have had less severe low back pain than in our group. If so, then the linear correlation noted in FIGURE 6 would predict no significant difference from normal subjects. Conversely, female LBP subjects with the lowest pain thresholds and highest MEAP – irm levels may have been making a transition from chronic low back pain to fibromyalgia . Half of our LBP group was male, introducing gender as a potentially confounding factor.
The FM group's results were distinctly different from the Normal and LBP groups. FM had widespread pain complaints, the highest Systemic Complaints scores, the lowest pain thresholds, and highest numbers of tender points of the 3 groups. Their SF-36 scores were intermediate between LBP and Normal groups. Widespread pain, low pain thresholds, and high Systemic Complaints scores differentiated FM from Normal and LBP. CSF MEAP – irm concentrations were approximately 3-fold higher in FM than Normal (figure 5). This confirmed earlier findings  where a group of women meeting an older set of fibromyalgia criteria [17, 18] had 34% higher CSF MEAP – irm concentrations than a group of 8 age-matched female control subjects . None of the FM subjects in the earlier group required analgesics or other medications suggesting that their symptoms may have been milder than for our FM group. Our group contained 1 male and 13 females. In contrast, Lui et al. found MEAP concentrations (peptide identity confirmed by HPLC) that were 38% lower in FM than control subjects (p < 0.01) . There was inadequate clinical data to compare the severity of complaints between these FM populations. These investigators also used a liquid-liquid peptide extraction method. The differences in FM severity, control groups, extraction procedures, and lack of sufficient CSF to identify precise peptides by HPLC  made it difficult to compare these sets of divergent results. Standardized measurements on CSF withdrawn from highly characterized and clearly defined subjects and controls will be required to resolve these inconsistencies.
This is the first investigation to examine the potential effect of co-existing CFS on MEAP – irm levels in FM. This suggested that the mechanism(s) of CFS were probably independent of those responsible for the elevated MEAP – irm levels in FM. Unfortunately, CFS subjects without FM could not be simultaneously tested to determine if their MEAP – irm levels were normal (as would be predicted).
Nociceptin – irm levels were the same in our three groups. The levels were about 10% of that found in women during labor . It was unclear if the higher concentrations were due to pregnancy, neurohormonal adaptations during labor and delivery, or the effects of acute pain. Again, the absence of a control group comparable to our pain-free Normal group makes mechanistic comparisons difficult.
The Normal group had Systemic Complaints and SF-36 scores in the normal ranges, high pain thresholds, low numbers of manual and dolorimetry-derived tender points and low cerebrospinal fluid MEAP and nociceptin concentrations. The LBP chronic regional pain group had similar Systemic Complaints scores, systemic pain thresholds and dolorimetry-defined tender point counts. However, most of their SF-36 results were near zero indicating the worst level of impairment of the 3 groups. MEAP – irm was just significantly elevated compared to the Normal group, and was correlated to the systemic pain threshold. The FM group was distinct since they had widespread pain complaints, the highest Systemic Complaints scores, the lowest pain thresholds, and highest numbers of tender points of the 3 groups. Their SF-36 scores were intermediate between the LBP and Normal groups. MEAP – irm concentrations were significantly higher in the FM than Normal group. The co-existence of Chronic Fatigue Syndrome with FM did not alter the MEAP – irm concentrations. This suggested that Chronic Fatigue Syndrome mechanism(s) did not involve preproenkephalin dysfunction. Nociceptin – irm levels were not different between these groups, and were lower than previously reported results from pregnant women in labor. Significant differences in MEAP – irm concentrations from previous studies may be due to the highly controlled definition of patients in this study, selection of control groups, and differences in peptide extraction methods.
functional magnetic resonance imaging
low back pain
short-form of 36 questions with the following domains: PF, physical functioning
role limitation due to physical problems
role limitation due to emotional problems
energy / fatigue
general perception of health
change in health
- Systemic Complaints domains:
ear, nose & throat
irritable bowel syndrome (Rome I criteria)
shortness of breath.
Special thanks to Dr. Lars Terenius, Karolinska Institute, for providing the antibodies and performing the radioimmunoassays for this study. The work was supported by Dept of Army Grant # DAMD17-00-2-0018 (GW, JC & DC), U.S. Public Health Service Award RO1 AI42403 (JNB), and 1 M01-RR13297-01A1 from the General Clinical Research Center Program of the National Center for Research Resources, National Institute of Health.
- Wolfe F, Smythe HA, Yunus MB, Bennett RM, Bombardier C, Goldenberg DL, Tugwell P, Campbell SM, Abeles M, Clark P: The American College of Rheumatology 1990 Criteria for the Classification of Fibromyalgia. Report of the Multicenter Criteria Committee. Arthritis Rheum. 1990, 33: 60-72.View ArticleGoogle Scholar
- Wolfe F: The relation between tender points and fibromyalgia symptom variables: evidence that fibromyalgia is not a discrete disorder in the clinic. Ann Rheum Dis. 1997, 56: 268-271.View ArticlePubMedPubMed CentralGoogle Scholar
- Coghill RC, McHaffie JC, Yen Y-F: Neural correlates of interindividual differences in the subjective experience of pain. Proc Natl Acad Sci USA. 2003, 100: 8538-8542. 10.1073/pnas.1430684100.View ArticlePubMedPubMed CentralGoogle Scholar
- Gracely RH, Petzke F, Wolf JM, Clauw DJ: Functional magnetic resonance imaging evidence of augmented pain processing in fibromyalgia. Arthritis Rheum. 2002, 46: 1333-1343. 10.1002/art.10225.View ArticlePubMedGoogle Scholar
- Bradley LA, McKendree-Smith NL, Alarcon GS: Pain complaints in patients with fibromyalgia versus chronic fatigue syndrome. Curr Rev Pain. 2000, 4: 148-157.View ArticlePubMedGoogle Scholar
- Fukuda K, Straus SE, Hickei I, Sharpe MC, Dobbins JC, Komaroff A: The chronic fatigue syndrome: a comprehensive approach to its definition and study. Ann Intern Med. 1994, 121: 953-959.View ArticlePubMedGoogle Scholar
- Lapossy E, Maleitzke R, Hrycaj P, Mennet W, Muller W: The frequency of transition of chronic low back pain to fibromyalgia. Scand J Rheumatol. 1995, 24: 29-33.View ArticlePubMedGoogle Scholar
- Yoshimasa T, Nakao K, Sakamoto M, Suda M, Morii N, Ikeda Y, Ishihara T, Manno M, Hamada S, Shimbo S: Demonstration and characterization of immunoreactive methionine-enkephalin, leucine-enkephalin, methionine-enkephalin-Arg6-Gly7-Leu8 and methionine-enkephalin-Arg6-Phe7 in human phaeochromocytoma. Acta Endocrinol (Copenh). 1984, 107: 261-267.Google Scholar
- Rosen A, Lundeberg T, Bytner B, Nylander I: Central changes in nociceptin, dynorphin B and Met-enkephalin-Arg-Phe in different models of nociception. Brain Res. 2000, 857: 212-218. 10.1016/S0006-8993(99)02432-4.View ArticlePubMedGoogle Scholar
- Spetea M, Rydelius G, Nylander I, Ahmed M, Bileviciute-Ljungar I, Lundeberg T, Svensson S, Kreicbergs A: Alteration in endogenous opioid systems due to chronic inflammatory pain conditions. Eur J Pharmacol. 2002, 435: 245-252. 10.1016/S0014-2999(01)01554-0.View ArticlePubMedGoogle Scholar
- Baraniuk JN, Clauw JD, Gaumond E: Rhinitis symptoms in chronic fatigue syndrome. Annals Allergy Asthma Immunol. 1998, 81: 359-365.View ArticleGoogle Scholar
- Ware JE, Sherbourne CD: The MOS 36-item short-form health survey (SF-36): I. Conceptual framework and item selection. Med Care. 1995, 30: 473-483.View ArticleGoogle Scholar
- Lyrenaes S, Nyberg F, Folkesson R, Lindberg B, Terenius L: Met-enkephalin-Arg6-Phe7 in human CSF. Increased levels in late pregnancy. Progress in Opioid Research. NIDA Res Monogr. 1986, 75: 430-433.Google Scholar
- Vaeroy H, Nyberg F, Terenius L: No evidence for endorphin deficiency in fibromyalgia following investigation of cerebrospinal fluid (CSF) dynorphin A and Met-enkephalin-Arg6-Phe7. Pain. 1991, 46: 139-143. 10.1016/0304-3959(91)90068-9.View ArticlePubMedGoogle Scholar
- Terenius L, Sandin J, Sakurada T: Nociceptin/orphanin FQ metabolism and bioactive metabolites. Peptides. 2000, 21: 919-922. 10.1016/S0196-9781(00)00228-X.View ArticlePubMedGoogle Scholar
- Giesecke T, Williams DA, Harris RE, Cupps TR, Tian X, Tian TX, Gracely RH, Clauw DJ: Subgrouping of fibromyalgia patients on the basis of pressure-pain thresholds and psychological factors. Arthritis Rheum. 2003, 48: 2916-2922. 10.1002/art.11272.View ArticlePubMedGoogle Scholar
- Yunus MB, Masi AT, Calabro JJ, Miller KA, Feigenbaum SL: Primary fibromyalgia (fibrositis): a clinical study of 50 patients with matched normal controls. Semin Arthritis Rheum. 1981, 11: 151-171. 10.1016/0049-0172(81)90096-2.View ArticlePubMedGoogle Scholar
- Smythe HA: Non-articular rheumatism and the fibrositis syndromes. In Arthritis and Allied Conditions. Edited by: Hollander E, McCarty DJ. 1972, Lea and Febviger, Philadelphia, PA, 11: 808-816. 8Google Scholar
- Liu Z, Welin M, Bragee B, Nyberg F: A high-recovery extraction procedure for quantitative analysis of substance P and opioid peptides in human cerebrospinal fluid. Peptides. 2000, 21: 853-860. 10.1016/S0196-9781(00)00219-9.View ArticlePubMedGoogle Scholar
- Lui DX, Wood GW, Desiderio DM: Proenkephalin A and proopiomelanocortin peptides in human cerebrospinal fluid. J Chromatogr. 1990, 530: 235-252.View ArticleGoogle Scholar
- Brooks H, Elton CD, Smart D, Rowbotham DJ, McKnight AT, Lambert DG: Identification of nociceptin in human cerebrospinal fluid: comparison of levels in pain and non-pain states. Pain. 1998, 78: 71-73. 10.1016/S0304-3959(98)00130-4.View ArticlePubMedGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2474/5/48/prepub
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.