The neuropharmacology of centrally-acting analgesic medications in fibromyalgia

An intricate relationship between pain and depression: clinical correlates, coactivation factors and therapeutic targets

INTRODUCTION

An apparent clinical relationship between pain and depression has long been recognized, which makes an enormous impact on the individual health care. At present, the practical implication of such overlapping symptomatology between pain and depression is not clear, but the prevalence estimates for depression are substantially inflated among patients with chronic pain and vice versa. This interaction has been labeled as the depression-pain syndrome or depression-pain dyad.

AREAS COVERED

This article discusses the neurobiological substrates and neuroanatomical pathways involved in pain-depression dyad along with newer therapeutic targets.

EXPERT OPINION

Several key themes emerged from our review of the relationship between depression and pain. First, the diagnosis of depression in pain or vice versa is particularly challenging, and the development of better diagnostic framework that involves both pain and depression is particularly required. Secondly, the entwined relationship between pain and depression supports the possibility of common coactivating factors that results in their neurophysiological overlap. A broad understanding of the role played by the central nervous system (CNS) in the processing of pain and depression may eventually lead to the introduction of triple reuptake inhibitors, agomelatine, vilazodone and ketamine with novel mechanism of action, hence appear to be of promising potential for pain with depression.

Quantitative electroencephalographic abnormalities in fibromyalgia patients

There is increasing acceptance that pain in fibromyalgia (FM) is a result of dysfunctional sensory processing in the spinal cord and brain, and a number of recent imaging studies have demonstrated abnormal central mechanisms. The objective of this report is to statistically compare quantitative electroencephalogram (qEEG) measures in 85 FM patients with age and gender matched controls in a normative database. A statistically significant sample (minimum 60 seconds from each subject) of artifact-free EEG data exhibiting a minimum split-half reliability ratio of 0.95 and test-retest reliability ratio of 0.90 was used as the threshold for acceptable data inclusion. FM subject EEG data was compared to EEGs of age and gender matched healthy subjects in the Lifespan Normative Database and analyzed using NeuroGuide 2.0 software. Analyses were based on spectral absolute power, relative power and coherence. Clinical evaluations included the Fibromyalgia Impact Questionnaire (FIQ), Beck Depression Inventory and Fischer dolorimetry for pain pressure thresholds. Based on Z-statistic findings, the EEGs from FM subjects differed from matched controls in the normative database in three features: (1) reduced EEG spectral absolute power in the frontal International 10-20 EEG measurement sites, particularly in the low- to mid-frequency EEG spectral segments; (2) elevated spectral relative power of high frequency components in frontal/central EEG measurement sites; and (3) widespread hypocoherence, particularly in low- to mid-frequency EEG spectral segments, in the frontal EEG measurement sites. A consistent and significant negative correlation was found between pain severity and the magnitude of the EEG abnormalities. No relationship between EEG findings and medicine use was found. It is concluded that qEEG analysis reveals significant differences between FM patients compared to age and gender matched healthy controls in a normative database, and has the potential to be a clinically useful tool for assessing brain function in FM patients.

Strategies for managing fibromyalgia

The presentation of fibromyalgia is heterogeneous, and the treatment approach should be individualized for each patient, depending on the severity of the patient's pain, the presence of other symptoms or comorbidities, and the degree of functional impairment. The management of fibromyalgia includes the identification and treatment of all pain sources that may be present in addition to fibromyalgia, such as peripheral pain generators (e.g., comorbid osteoarthritis or neuropathic pain) or visceral pain (e.g., comorbid irritable bowel syndrome). It is also important to address other symptoms or disorders that commonly occur in patients with fibromyalgia, such as fatigue, sleep disturbances, cognitive impairment, stiffness, and mood or anxiety disorders. Finally, the treatment should strive to improve the patient's function and global health status. In most cases, the management of fibromyalgia involves both pharmacologic and nonpharmacologic treatments. This report provides an in-depth review of randomized, controlled trials for pharmacologic and nonpharmacologic approaches to fibromyalgia therapy.

Growth hormone as concomitant treatment in severe fibromyalgia associated with low IGF-1 serum levels. A pilot study

Background

There is evidence of functional growth hormone (GH) deficiency, expressed by means of low insulin-like growth factor 1 (IGF-1) serum levels, in a subset of fibromyalgia patients. The efficacy of GH versus placebo has been previously suggested in this population. We investigated the efficacy and safety of low dose GH as an adjunct to standard therapy in the treatment of severe, prolonged and well-treated fibromyalgia patients with low IGF-1 levels.

Methods

Twenty-four patients were enrolled in a randomized, open-label, best available care-controlled study. Patients were randomly assigned to receive either 0.0125 mg/kg/d of GH subcutaneously (titrated depending on IGF-1) added to standard therapy or standard therapy alone during one year. The number of tender points, the Fibromyalgia Impact Questionnaire (FIQ) and the EuroQol 5D (EQ-5D), including a Quality of Life visual analogic scale (EQ-VAS) were assessed at different time-points.

Results

At the end of the study, the GH group showed a 60% reduction in the mean number of tender points (pairs) compared to the control group (p < 0.05; 3.25 ± 0.8 vs. 8.25 ± 0.9). Similar improvements were observed in FIQ score (p < 0.05) and EQ-VAS scale (p < 0.001). There was a prompt response to GH administration, with most patients showing improvement within the first months in most of the outcomes. The concomitant administration of GH and standard therapy was well tolerated, and no patients discontinued the study due to adverse events.

Conclusion

The present findings indicate the advantage of adding a daily GH dose to the standard therapy in a subset of severe fibromyalgia patients with low IGF-1 serum levels.

Trial Registration

NCT00497562 (ClinicalTrials.gov).

Biology and therapy of fibromyalgia. New therapies in fibromyalgia

Fibromyalgia is a chronic, musculoskeletal pain condition that predominately affects women. Although fibromyalgia is common and associated with substantial morbidity and disability, there are no US Food and Drug Administration-approved treatments. However, progress has been made in identifying pharmacological and non-pharmacological treatments for fibromyalgia. Recent pharmacological treatment studies have focused on selective serotonin and norepinephrine reuptake inhibitors, which enhance serotonin and norepinephrine neurotransmission in the descending pain pathways and lack many of the adverse side effects associated with tricyclic medications. Promising results have also been reported for medications that bind to the α₂δ subunit of voltage-gated calcium channels, resulting in decreased calcium influx at nerve terminals and subsequent reduction in the release of several neurotransmitters thought to play a role in pain processing. There is also evidence to support exercise, cognitive behavioral therapy, education, and social support in the management of fibromyalgia. It is likely that many patients would benefit from combinations of pharmacological and non-pharmacological treatments, but more study is needed.

Mechanisms underlying development of spatially distributed chronic pain (fibromyalgia)

Chronic fibromyalgia (FM) pain is prevalent (estimated as high as 13%), predominantly affects women, and is associated with a variety of focal pain conditions. Ongoing FM pain is referred to deep tissues and is described as widespread but usually is maximally located within a restricted region such as the shoulders. Palpation of deep tissues reveals an enhanced nociceptive sensitivity that is not restricted to regions of clinical pain. Similarly, psychophysical testing reveals allodynia and hyperalgesia for cutaneous stimulation at locations beyond regions of clinical pain referral. The combination of widely distributed clinical pain and generalized hypersensitivity is highly disabling, but no satisfactory treatment is regularly prescribed. A thorough understanding of mechanisms will likely be required to develop and document adequate therapies. The generalized hypersensitivity associated with FM has focused considerable interest on central (CNS) mechanisms for the disorder. These include central sensitization, central disinhibition and a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis. However, the central effects associated with FM can be produced by a peripheral source of pain. Chronic nociceptive input induces central sensitization, magnifying pain, and it activates the HPA and the sympathetic nervous system. Chronic sympathetic activation indirectly sensitizes peripheral nociceptors and sets up a vicious cycle. Thus, it appears that central mechanisms of FM pain are dependent on abnormal peripheral input(s) for development and maintenance of this condition. A substantial literature defines peripheral-CNS-peripheral interactions that are integral to FM pain. These reciprocal actions and related phenomena of relevance to FM pain are reviewed here, leading to suggestions for testing of therapeutic approaches.

Current trends in fibromyalgia research

The development of standardised criteria for the diagnosis of fibromyalgia in 1990 has allowed careful study of this chronically painful syndrome. Epidemiological studies show increased symptoms and disability in patients with fibromyalgia, compared with other conditions associated with chronic, widespread pain. In addition, prevalence and severity of fibromyalgia symptoms are increased in women. Current studies have identified strong evidence for central sensitisation in fibromyalgia. Data from these studies may expand effective treatment options for fibromyalgia.

Impact of fibromyalgia pain on health-related quality of life before and after treatment with tramadol/acetaminophen

OBJECTIVE

To assess health-related quality of life (HRQOL) in patients with moderate-to-severe fibromyalgia pain compared with the general population, and to assess the relationship between pain severity and HRQOL before and after treatment with an analgesic.

METHODS

Data were obtained from a randomized, double-blind study of patients with moderate-to-severe fibromyalgia pain. Patients received either tramadol/acetaminophen or placebo 4 times/day as needed for 91 days. HRQOL was measured with the Short Form 36 Health Survey (SF-36) and the Fibromyalgia Impact Questionnaire (FIQ). Baseline HRQOL scores were compared with a national sample of noninstitutionalized adults and a sample of patients with impaired HRQOL due to congestive heart failure. Patients with fibromyalgia were divided into tertiles by change in pain severity, and SF-36 scores were compared across the tertiles. Mean changes in SF-36 and FIQ scores were compared between treatment groups.

RESULTS

Patients with fibromyalgia scored lower than the US norm on all SF-36 scales (P < 0.0001) and lower than patients with congestive heart failure on most scales. More severe pain was associated with greater impairment of HRQOL compared with less severe pain (P < 0.0001). Patients in the highest tertile for improved pain severity had greater improvement in HRQOL scores than patients in the lower tertiles. Compared with patients who received placebo (n = 157), patients treated with tramadol/acetaminophen (n = 156) showed greater improvement on SF-36 physical functioning, role physical, bodily pain, and physical summary scales, as well as FIQ scales for ability to do job, pain, and stiffness (P < 0.01).

CONCLUSION

Moderate-to-severe fibromyalgia pain significantly impairs HRQOL, and effective pain relief in these patients significantly increases HRQOL.

The Monoamine Reuptake Inhibitor Milnacipran Does Not Affect Nociception to Acute Visceral Distension in Rats

The role of antidepressants in the treatment of visceral pain has not been extensively examined. Milnacipran, an antidepressant that inhibits monoamine reuptake, is widely used in the treatment of depression and fibromyalgia. In this study, we sought to determine the activity of milnacipran against acute visceral nociception. Female virgin rats were studied 7 days after bilateral ovariectomy. For uterine cervical distension (UCD), two metal rods were inserted into the cervical osses under general anesthesia for manual distension. Colorectal distension (CRD) was performed by insertion of a balloon catheter into the descending colon and rectum, followed by manual inflation. Two electrodes were inserted into the rectus abdominus muscle for recording UCD- or CRD-induced reflex contraction, which was quantified by electromyography (EMG). A dose response for milnacipran, administered intrathecally or i.v., was obtained for UCD and CRD stimulation. Milnacipran failed to inhibit the UCD-induced EMG response, whether administered i.v. or intrathecally. Similarly, i.v. milnacipran, administered either acutely or chronically, failed to inhibit the CRD-induced EMG response. CRD and UCD are well established animal models for the study of acute visceral pain. Milnacipran, although it provides some unique advantages compared with other antidepressants, is unlikely to produce analgesia after acute administration in the setting of acute visceral pain.

IMPLICATIONS

Neither intrathecal nor i.v. milnacipran, a monoamine reuptake inhibitor, inhibits an acute visceral pain response induced by colorectal or uterine cervical distension.

Persistent pain and depression: a biopsychosocial perspective

This review highlights recent research findings on the relationship between persistent pain and depression and discusses the implications of these findings for future research in persons who suffer from both pain and depression. First, we briefly discuss advances in theories of pain that underscore the important role that depression can play in the chronic pain experience. Second, we discuss depression in persons suffering from chronic pain from a biopsychosocial perspective that takes into account both biological and psychosocial mechanisms linking pain and depression. Third, we address biomedical, psychosocial, and combined medical-psychosocial approaches to treatment in persons with persistent pain and depression. We conclude by highlighting future directions for research related to screening and diagnosis of depression in persons having persistent pain, treatment of comorbid pain and depression, and individual and subgroup differences in the experience of persistent pain and depression.

Pharmacological therapies in fibromyalgia

The fibromyalgia syndrome (FMS) is a common, chronic, widespread pain disorder that mainly affects middle-aged women. In addition to pain complaints, fatigue and disturbed sleep are symptoms frequently reported by these patients. Many FMS patients also meet diagnostic criteria for mood disorders (e.g. depression) as well as other so-called 'functional somatic syndromes', including irritable bowel syndrome, temporomandibular joint disorder, and subsets of chronic low-back pain. A wide variety of medications are used to manage the eclectic symptomatology of FMS patients, although relatively few have been rigorously tested. This chapter provides a contemporary update of the state of FMS pharmacotherapy, with an emphasis on compounds that have been tested in double-blind, randomized, controlled trials. Particular attention is paid to the efficacy of these therapies on the associated symptoms and co-morbid syndromes commonly seen in FMS patients.

Tramadol and acetaminophen combination tablets in the treatment of fibromyalgia pain: a double-blind, randomized, placebo-controlled study

PURPOSE

To evaluate the efficacy and safety of a combination analgesic tablet (37.5 mg tramadol/325 mg acetaminophen) for the treatment of fibromyalgia pain.

METHODS

This 91-day, multicenter, double-blind, randomized, placebo-controlled study compared tramadol/acetaminophen combination tablets with placebo. The primary outcome variable was cumulative time to discontinuation (Kaplan-Meier analysis). Secondary measures at the end of the study included pain, pain relief, total tender points, myalgia, health status, and Fibromyalgia Impact Questionnaire scores.

RESULTS

Of the 315 subjects who were enrolled in the study, 313 (294 women [94%], mean [+/- SD] age, 50 +/- 10 years) completed at least one postrandomization efficacy assessment (tramadol/acetaminophen: n = 156; placebo: n = 157). Discontinuation of treatment for any reason was less common in those treated with tramadol/acetaminophen compared with placebo (48% vs. 62%, P = 0.004). Tramadol/acetaminophen-treated subjects also had significantly less pain at the end of the study (53 +/- 32 vs. 65 +/- 29 on a visual analog scale of 0 to 100, P <0.001), and better pain relief (1.7 +/- 1.4 vs. 0.8 +/- 1.3 on a scale of -1 to 4, P <0.001) and Fibromyalgia Impact Questionnaire scores (P = 0.008). Indexes of physical functioning, role-physical, body pain, health transition, and physical component summary all improved significantly in the tramadol/acetaminophen-treated subjects. Discontinuation due to adverse events occurred in 19% (n = 29) of tramadol/acetaminophen-treated subjects and 12% (n = 18) of placebo-treated subjects (P = 0.09). The mean dose of tramadol/acetaminophen was 4.0 +/- 1.8 tablets per day.

CONCLUSION

A tramadol/acetaminophen combination tablet was effective for the treatment of fibromyalgia pain without any serious adverse effects.