Elevated cerebrospinal fluid levels of substance P in patients with the fibromyalgia syndrome

Current concepts in the pathophysiology of abnormal pain perception in fibromyalgia

Fibromyalgia is a noninflammatory rheumatic disorder characterized by chronic widespread musculoskeletal pain. Although many studies have described the pain and other clinical symptoms associated with this disorder, the primary mechanisms underlying the etiology of fibromyalgia remain elusive. This article reviews recent data supporting the links among each of three systems--the musculoskeletal system, the neuroendocrine system, and the central nervous system (CNS), all of which appear to play major roles in fibromyalgia pathophysiology--and pain in fibromyalgia, and concludes by presenting a model of the pathophysiology of abnormal pain perception in fibromyalgia which integrates the research findings described.

Abnormal functional activity of the central nervous system in fibromyalgia syndrome

The evaluation of pain is one of the major problems facing general practitioners and specialists in medicine. Although the source of pain can be usually be traced to specific abnormalities in a given organ system, some patients present with generalized pain syndromes, such as fibromyalgia, for which no specific source can be found. Some researchers have begun to consider that although there may be a somatic source of such pain at its initiation, over time the pain may be maintained or exacerbated by functional alterations in critical regions of the brain and spinal cord that are involved in pain processing or pain inhibition. This article describes the techniques currently used to measure regional cerebral blood flow (rCBF) in the brain by single photon emission computed tomography (SPECT) imaging, and reviews the SPECT and positron emission tomography literature concerning alterations in functional brain activity associated with pain in healthy individuals and in patients with chronic pain, including those with fibromyalgia. The article concludes by describing the implications of current knowledge about pain and abnormal functional brain activity in the understanding of the pathophysiology of fibromyalgia and in the development of therapeutic strategies to manage patients with this disorder.

A possible role for saliva as a diagnostic fluid in patients with chronic pain

OBJECTIVES

The focus of this review was on proteins and peptides found in saliva. Of greatest interest were those neuropeptides relevant to nociception and to the pathogenesis of chronic pain syndromes. An additional goal was to develop a standardized protocol to collect saliva for laboratory assessment.

METHODS

Data were obtained through discussion with experts at the medical schools in San Antonio and Heidelberg and a Medline literature search involving all relevant studies from 1966 to 1997. The literature search was based on the following key terms: saliva, serotonin, neuropeptide, substance P (SP), calcitonin gene-related peptide (CGRP), and nerve growth factor (NGF).

RESULTS

The mean concentration of SP in the saliva of healthy normal controls ranged from 9.6 to 220 pg/mL. Generally, the concentration of SP was approximately three times higher in saliva than in plasma. In a number of painful conditions, particularly tension headache, substantial elevations of salivary SP were found. Mean values for salivary CGRP in healthy controls were approximately 22 pmol/L and were significantly elevated in patients with migraine attacks or cluster headache. There were no data to indicate prior quantitative determination of NGF in human saliva.

CONCLUSIONS

After sampling and processing techniques have been standardized, measurement of neuropeptides in human saliva could provide a valuable tool for study of patients with chronic painful disorders such as rheumatoid arthritis, osteoarthritis, and even fibromyalgia syndrome.

Advances in fibromyalgia: possible role for central neurochemicals

The neurophysiologic term allodynia has been applied to fibromyalgia because people with that disorder experience pain from pressure stimuli which are not normally painful. The nociceptive neurotransmitters of animal studies are now relevant to this human model of chronic, widespread pain. Evidence is presented to implicate several chemical pain mediators (including serotonin, substance P, nerve growth factor, and dynorphin A) in the pathogenesis of fibromyalgia. This perception is hopeful because it offers many new options for the development of innovative therapy.

Elevated cerebrospinal fluid substance P-like immunoreactivity in patients with painful osteoarthritis, but not in patients with rhizopatic pain from a herniated lumbar disc

Cerebrospinal fluid (CSF) levels of substance P like immunoreactivity (SPLI) were determined in 11 patients with painful osteoarthritis in hip or knee, 9 patients with rhizopatic pain from a herniated lumbar disc, and in 9 healthy volunteers without pain. The patients with osteoarthritis had increased levels of SPLI in CSF (p < 0.001) compared to the controls. A positive correlation was also seen between the CSF SPLI and the degree of pain. At a second lumbar puncture 5 months after operation, SPLI had decreased, but was still significantly higher than in the controls. No difference in CSF SPLI was seen in the patients with herniated lumbar disc compared to the controls, neither before treatment, nor at follow up CSF postoperatively. The results suggest that nociceptive joint pain is consistent with increased SPLI in CSF. Differences in SPLI in CSF may be useful to differentiate pain from various origin, and may also increase our understanding of different pain mechanisms.

Elevated cerebrospinal fluid level of substance P and decreased undecapeptidase activity at term pregnancy

This paper reports a study of substance P and its converting enzyme substance P endopeptidase (SPE) in cerebrospinal fluid (CSF) collected from women at term pregnancy. A method was developed to assess the CSF levels of substance P itself with minimum contribution from prestages or fragments of the undecapetide. The measured activity was compared with that detected in CSF from control, non-pregnant, non-puerperal women. The result indicates a significant increase in substance P-like immunoreactivity at term pregnancy (19.9 +/- 3.9 fmol/ml, n = 10) compared with that of control subjects (12.3 +/- 2.8 fmol/ml, n = 9; P < 0.001). This elevation was suggested to reflect an increased activity in spinal sensory neurons at this stage of pregnancy. The activity of SPE was assessed by measuring the product substance P1-7 by a radioimmunoassay specific for this fragment. It was found that the enzyme activity was significantly decreased in CSF from pregnant women (11.2 +/- 0.71 pmol/h.ml), compared with control samples (18.4 +/- 0.73 pmol/h.ml; P < 0.05). Moreover, a significant negative correlation was found to exist between the level of substance P and the activity of SPE (P < 0.05, r2 = 0.65), suggesting that the enzyme may be involved in a mechanism regulating the level of substance P concentration.

The fibromyalgia syndrome

The term fibromyalgia describes a complex syndrome characterized by pain amplification, musculoskeletal discomfort, and systemic symptoms. Although its existence has been controversial, nearly all rheumatologists now accept fibromyalgia as a distinct diagnostic entity. In fact, in the United States it is the third or fourth most common reason for rheumatology referral. Exciting new insights into the aetiology, pathogenesis, diagnosis and treatment of fibromyalgia will be reviewed.

A randomized, double-blind crossover trial of fluoxetine and amitriptyline in the treatment of fibromyalgia

OBJECTIVE

To study the effect of fluoxetine (FL) and amitriptyline (AM), alone and in combination, in patients with fibromyalgia (FM).

METHODS

Nineteen patients with FM completed a randomized, double-blind crossover study, which consisted of 4 6-week trials of FL (20 mg), AM (25 mg), a combination of FL and AM, or placebo. Patients were evaluated on the first and last day of each trial period. Outcome measures included a tender point score, the Fibromyalgia Impact Questionnaire (FIQ), the Beck Depression Inventory (BDI) scale, and visual analog scales (VAS) for global well-being (1 completed by the physician and 1 by the patient), pain, sleep trouble, fatigue, and feeling refreshed upon awakening.

RESULTS

Both FL and AM were associated with significantly improved scores on the FIQ and on the VAS for pain, global well-being, and sleep disturbances. When combined, the 2 treatments worked better than either medication alone. Similar, but nonsignificant, improvement occurred in the BDI scale, the physician global VAS, and the VAS for fatigue and feeling refreshed upon awakening. Trends were less clear for the tender point score.

CONCLUSION

Both FL and AM are effective treatments for FM, and they work better in combination than either medication alone.

Nitric oxide mediates long-term hyperalgesic and antinociceptive effects of the N-terminus of substance P in the formalin assay in mice

Conditions such as hyperalgesia can occur days or months after the noxious insult. Substance P (SP) is released in response to noxious stimuli. Given the long-term effects of the N-terminus of SP on putative nociceptive transmitters, we investigated changes in formalin-induced nociception following an accumulation of SP N-terminal metabolites in mice. Pre-treatment with the N-terminal metabolite of SP, SP(1-7), was without effect when injected intrathecally (i.t.) 5 or 30 min before formalin. However, at 24 h, SP(1-7) increased behaviors during Phase 1, indicating hyperalgesia, and attenuated Phase 2 responses, consistent with antinociception. The nitric oxide (NO) synthase inhibitor, N omega-nitro-L-arginine methyl ester HCl (L-NAME), blocked both hyperalgesic and antinociceptive effects when co-injected with SP(1-7). Consistent with a NO-mediated pathway, L-arginine (L-arg), the N-terminal amino acid of SP and precursor to NO, mimicked the antinociceptive effect of SP(1-7) on Phase 2. The hyperalgesic effect of SP(1-7) in Phase 1, which was not mimicked by L-arg, was prevented by D-SP(1-7), a SP(1-7) antagonist. Thus, SP(1-7) modulates nociception via two distinct NO-mediated pathways. When injected for 7 days, tolerance developed to the antinociceptive effect of SP(1-7) on Phase 2, but not to the hyperalgesic effect on Phase 1. Intraperitoneally injected SP(1-7) also produced hyperalgesia during Phase 1, to which tolerance developed following seven daily injections. Together, these data support the hypothesis that an accumulation of SP N-terminal metabolites, either peripherally or within the spinal cord area, is sufficient for long-term modulation of multiple types of nociception with hyperalgesic responses being most persistent.

Non-nociceptive aspects of persistent musculoskeletal pain

Persistent pain is often difficult to understand and to treat. Clinical and neurophysiological evidence is offered, suggesting that this often occurs because persistent pain is partially or wholly of non-nociceptive afferent origin. The concept of non-nociceptive pain and the potential roles of proprioceptive afferents in the production of non-nociceptive pain are particularly emphasized. It is suggested that non-nociceptive pain is often an important component of pain associated with peripheral and central neuropathy, fibromyalgia, trauma-induced pain, idiopathic low back pain, and chronic regional pain syndrome. Non-nociceptive pain is often dependent upon central sensitization induced by prior or ongoing nociception. Therapeutic methods which minimize nociceptive afferent activity are important in the prevention and/or elimination of often intractable non-nociceptive pain.

Generalized hypervigilance in fibromyalgia: evidence of perceptual amplification

The hypervigilance model of pain perception states that chronic pain patients have a heightened sensitivity to pain (e.g. low threshold and tolerance) because of increased attention to external stimulation and a preoccupation with pain sensations. This study tested the hypothesis that individuals with fibromyalgia, a chronic pain disorder of undetermined origin, have a generalized hypervigilant pattern of responding that extends beyond the pain domain. Twenty fibromyalgia out-patients, 20 rheumatoid arthritis (RA) patients, and 20 normal controls served as subjects. The RA and normal control subjects were age and sex matched to the fibromyalgia patients. Subjects were tested for pain tolerance, pain threshold, and noise tolerance and were asked to complete a number of questionnaires that assessed hypervigilance. As predicted, the responses of the fibromyalgia patients to both the pain and auditory stimuli were consistent with the generalized hypervigilance hypothesis. These patients had significantly lower threshold and tolerance values than the RA patients, who in turn, had lower values than the normal control subjects. The results of the psychological questionnaires revealed that the fibromyalgia and RA patients preferred lower levels of external stimulation than the control subjects. The outcome of this study supports the generalized hypervigilance hypothesis, suggesting that fibromyalgia patients have a perceptual style of amplification. The implications of these findings for understanding the role of biological, cognitive, and perceptual factors in pain disorders are discussed.

Psychiatric diagnoses in patients with fibromyalgia are related to health care-seeking behavior rather than to illness

OBJECTIVE

To compare the frequency of lifetime psychiatric disorders among 3 groups of subjects: patients with fibromyalgia syndrome (FMS) from a tertiary care setting, community residents with FMS who had not sought medical care for their FMS symptoms ("FMS nonpatients"), and healthy controls.

METHODS

We used the Computerized Diagnostic Interview Schedule to assess lifetime psychiatric diagnoses, as well as the Center for Epidemiological Studies Depression scale and the Trait Anxiety Inventory to assess current psychological distress, among 64 patients with FMS, 28 FMS nonpatients, and 23 healthy individuals.

RESULTS

Patients with FMS, relative to FMS nonpatients and healthy controls, were characterized by a significantly greater number of lifetime psychiatric diagnoses (P = 0.002). Nonpatients did not differ from controls in psychiatric diagnoses. Patients also exhibited higher psychological distress levels than nonpatients, and nonpatients showed greater distress than controls. Differences in psychological distress between patients and nonpatients were eliminated after controlling for pain threshold and fatigue ratings.

CONCLUSION

Psychiatric disorders are not intrinsically related to the FMS syndrome. Instead, multiple lifetime psychiatric diagnoses may contribute to the decision to seek medical care for FMS in tertiary care settings.

The lymphocyte phenotype in patients with primary fibromyalgia

The aim of this study was to examine the lymphocyte phenotype in fibromyalgia (FB) patients. Nineteen patients [18 females, 1 male] who met the ACR classification criteria for FB were recruited into the study. The fluorescence of leukocytes was measured using Ortho Cytotron Absolute flow cytometer. Ortho-mune monoclonal antibodies [OK-Combo-Tests] were used for determination of the following antigens: CD3/CD19, CD3/HLA-DR, CD4/CD8, CD45RA/CD4. Serum IgE was established with ELISA [Merck, Germany]. There were no differences in percentage of CD3, CD19, CD4, CD8, CD3/HLA-DR and CD4/CD45RA cells as compared to healthy controls. We found a negative correlation between CD4 and CD8, CD3DR and IgE, CD8 and IgE concentration. The positive correlation between CD3 and CD3DR, CD3DR and CD8 was observed. The inhibitory effect of CD8+ cells subpopulation on B-cells and thereby on IgE production in patients afflicting for allergy has been already observed. Moreover, the symptoms to allergy has been found in about 50% of our patients. Taken together the data thus far obtained present a coexistence of symptoms of allergy and FB.

Fibromyalgia in women. Abnormalities of regional cerebral blood flow in the thalamus and the caudate nucleus are associated with low pain threshold levels

OBJECTIVE

To determine if regional cerebral blood flow (rCBF) in the left and right hemithalami or the left and right heads of the caudate nucleus is abnormal in women with fibromyalgia (FM).

METHODS

Resting-state rCBF in the hemithalami and left and right heads of the caudate nucleus of 10 untreated women with FM and 7 normal control women was measured by single-photon-emission computed tomography. Pain threshold levels at tender and control points also were assessed in both the women with FM and the controls.

RESULTS

The rCBF in the left and right hemithalami and the left and right heads of the caudate nucleus was significantly lower in women with FM than in normal controls (P = 0.01, P = 0.003, P = 0.01, and P = 0.02, respectively). Compared with controls, the women with FM also were characterized by significantly lower cortical rCBF (P = 0.001) and lower pain threshold levels at both tender points (P = 0.0001) and control points (P = 0.0001).

CONCLUSION

The findings of low rCBF and generalized low pain thresholds support the hypothesis that abnormal pain perception in women with FM may result from a functional abnormality within the central nervous system.

Inhibition of the production and effects of interleukin-1 and tumor necrosis factor alpha in rheumatoid arthritis

This review has summarized information published over the last 5 years on the presence and pathophysiologic role of IL-1 and TNF alpha in RA. The evidence to date shows that 5 of 6 criteria for identifying mediators of tissue damage in human autoimmune diseases are satisfied (Table 1). The last criterion, prevention of clinical progression in patients with RA, is currently being evaluated. Many new therapeutic approaches are currently being developed, including the use of soluble receptors to IL-1 or TNF, monoclonal antibodies to TNF alpha, a specific IL-1 receptor antagonist, and gene therapy with the latter molecule. It should be emphasized that both IL-1 and TNF alpha play important roles in normal host defense; the possible complications of blocking their production or effects need to be carefully evaluated in long-term studies. A recent review has emphasized that although IL-1 and TNF alpha have many overlapping biologic properties, each may exhibit distinct effects in joint disease (99). Anti-TNF treatment may be primarily antiinflammatory but blocking IL-1 may be more effective in preventing cartilage destruction (100). The possibility exists that simultaneous inhibition of TNF alpha and IL-1 may be more therapeutically efficacious than blockade of either agent alone, as was recently demonstrated with IL-1ra and soluble TNF receptors in bacterial cell wall-induced arthritis in rats (101). The next level of clinical studies in rheumatoid arthritis should include the use of two biologic response modifiers together, or one agent combined with a more traditional form of therapy.