Antidepressants for fibromyalgia: Latest word on the link to depression and anxiety
Why should fibromyalgia—an ostensible musculoskeletal disorder—be of interest to you? Because you can help relieve the depressed mood, anxiety, fatigue, and insomnia that often accompany this chronic, debilitating disorder.
Patients with fibromyalgia often resist being referred to a psychiatrist because they fear being told their pain and other somatic symptoms are “all in their heads.” Evidence is mounting that they may be literally correct—the symptoms of fibromyalgia appear to have a physiologic connection with the central nervous system. Abnormal CNS activity, including sleep patterns, response to stress, pain processing, and neurotransmitter levels, has been documented in patients with fibromyalgia.
As psychiatrists, we can reassure these patients—and their primary care physicians and rheumatologists—that we are in a position to help because we:
- have expertise in assessing mood and anxiety disorders and in managing antidepressants, the medication physicians most commonly prescribe for fibromyalgia;
- are skilled in the use of the anticonvulsant gabapentin, which is being used in fibromyalgia for its analgesic and sedative effects;
- can offer much-needed support through psychotherapy, as chronic pain and other fibromyalgia-related symptoms create great stress in these patients’ lives.
Antidepressants are showing promise as an effective treatment for pain, fatigue, and depression in patients with fibromyalgia in studies by our group and others. The following information can help you stay current with the newest understandings of this ailment.
CRITERIA FOR DIAGNOSING FIBROMYALGIA
History of widespread pain
Pain in 11 of 18 tender point sites on digital palpation
Digital palpation should be performed with an approximate force of 4 kg.
Figure 1 LOCATION OF FIBROMYALGIA TENDER POINTS
To palpate tender point sites, pressure is applied with the thumb pad perpendicularly to each site and the force increased by 1 kg per second until 4 kg of pressure is achieved. Whitening of the thumbnail bed usually occurs when applying the 4-kg force.
Mood disorders in fibromyalgia
A diagnosis of fibromyalgia requires the finding of widespread pain and tenderness at specific anatomic points (Table 1, Figure 1).1 Most patients also report fatigue, sleep disturbance, and morning stiffness (Box 1).2-5 American College of Rheumatology criteria do not require exclusionary tests such as radiographs and blood tests for the diagnosis.
Primary care physicians are increasingly making the diagnosis themselves and referring patients to rheumatologists only when conditions other than fibromyalgia are suspected. The differential diagnosis is broad, and other rheumatic and nonrheumatic disorders have similar symptoms, require different treatment, and affect fibromyalgia management (Table 2). 6
Patients with fibromyalgia often report symptoms of major depressive disorder, such as depressed mood, anxiety, fatigue, and insomnia.7 Many psychological studies of such patients have documented increased rates of depressive symptoms.8 Depression and anxiety symptoms are common and frequently severe, even among individuals with fibromyalgia in the general population.9
Patients’ mood and anxiety disorders correlate highly with the number of medically unexplained symptoms and are associated with functional disability. 10 The presence of psychological symptoms predicts persistent fibromyalgia symptoms,11 and psychological distress is strongly associated with symptom severity.12
Evidence for a CNS link
CNS mechanisms appear to contribute to the development of clinical findings in fibromyalgia.
Abnormal sleep A qualitative defect in sleep has been identified in patients with fibromyalgia.13 This sleep abnormality consists of inappropriate intrusion of alpha waves (normally seen during wakefulness or REM sleep) into deep sleep (usually characterized by delta waves).13 Some researchers believe alpha-delta sleep intrusion is associated with the chronic musculoskeletal pain and fatigue of fibromyalgia and, in turn, is mediated by an abnormality in central serotonergic neurotransmission.14 This sleep abnormality is not specific to fibromyalgia and can be found in other conditions, however.15 Debate continues regarding the role of sleep dysregulation in the pathophysiology of fibromyalgia.
CLINICAL FEATURES OF FIBROMYALGIA
Fibromyalgia is more common in women than men, with an estimated prevalence of 2% in the general population (3.4% in women and 0.5% in men). Its prevalence increases with age, rising sharply in middle age and then dropping off after age 80.2
Fibromyalgia is seen most often in women ages 50 and older.2 It occurs in 5% to 6% of patients presenting to general medical and family practice clinics and in 15% to 20% of patients presenting to rheumatologists, making it one of the most common diagnoses in office-based rheumatology practices.
American College of Rheumatology criteria may require only widespread pain and tenderness for a diagnosis of fibromyalgia, but most patients (73% to 85%) also report fatigue, sleep disturbance, and morning stiffness. Many (45% to 69%) report “pain all over,” paresthesias, headache, and anxiety. Co-occurring irritable bowel syndrome, sicca symptoms, and Raynaud’s phenomenon are less common (<35%).1 Patients with fibromyalgia also have high lifetime rates of other comorbid disorders, including migraine, chronic fatigue syndrome, and mood and anxiety disorders. Some patients report weakness, forgetfulness, difficulties in concentration, urinary frequency, history of dysmenorrhea, and restless legs.
Fibromyalgia is chronic, debilitating, and often leads to substantial functional impairment.3 Most patients with fibromyalgia do not display significant improvement over an average of 7 years of treatment.4 Patients with fibromyalgia report lower quality of well-being than patients with diagnoses of chronic obstructive pulmonary disease, rheumatoid arthritis, atrial fibrillation, advanced cancer, and several other chronic diseases.5
Stress response Stress appears to precipitate or exacerbate fibromyalgia symptoms in many patients.16 For example, fibromyalgia appears to be associated with victimization (adult and childhood sexual, physical, and emotional trauma), and this stress may trigger the development of fibromyalgia in some patients.17
Patients with fibromyalgia appear to develop disturbances in the two major stress-response systems: the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system.16 Although the interpretation of these disturbances is still debated, some researchers suggest that the available data point to reduction in CNS corticotropin releasing hormone (CRH), the key mediator in the HPA axis.18,19 CRH is also a behaviorally active peptide that leads to physiologic and behavioral arousal when administered centrally to animals.18 CRH reduction could contribute to the clinical features of fibromyalgia (e.g., fatigue) either directly or indirectly by causing a relative glucocorticoid deficiency.18,19
DIFFERENTIAL DIAGNOSIS OF FIBROMYALGIA
Systemic lupus erythematosus
Adapted from Clauw DJ. Fibromyalgia syndrome: an update on current understanding and medical management. Rheumatol Grand Rds 2000;3:1-9.
Fibromyalgia is also associated with moderate basal hypocortisolism. 18,19 A relative glucocorticoid deficiency could contribute to fibromyalgia’s characteristic fatigue, arthralgias, myalgias, and disturbances in mood and sleep.18 This deficiency may also cause some of the immunologic disturbances seen with fibromyalgia.18,19
Atypical depression, which shares such features of fibromyalgia as profound lethargy, is also associated with inappropriately normal or reduced activation of the HPA axis and a functional deficit in the release of hypothalamic CRH.18 The unifying feature of HPA axis activity in both atypical depression and fibromyalgia may be a shared hypofunctioning.18 A more complete understanding of the neuroendocrine changes in fibromyalgia awaits further study.
Pain processing Aberrant CNS processing of pain may also play a role in fibromyalgia.16,20 Fibromyalgia is sometimes precipitated by physical trauma.21 A traumatic injury may start a process in susceptible individuals that leads to an enhanced central processing of painful stimuli characteristic of central sensitization.22 Patients with fibromyalgia often develop an increased response to painful stimuli (hyeralgesia) and experience pain from normally nonnoxious stimuli (allodynia).20
Substance P, an important nociceptive neurotransmitter, may have a role in generating central sensitization.23 Elevated concentrations of substance P have been found in the cerebrospinal fluid (CSF) of individuals with fibromyalgia.24 Substance P also inhibits CRH release and may contribute to low CRH activity in fibromyalgia.16
Neurotransmitter defects A functional reduction in serotonergic activity has been demonstrated in patients with fibromyalgia. Schwarz et al25 found a strong negative correlation between serum concentrations of the primary serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and substance P, pain, and insomnia. Evidence also exists of reduced concentrations of the primary norepinephrine metabolite, 3-methoxy-4-hydroxyphenethylene (MHPG), in the CSF of patients with fibromyalgia.26 Reduced serotonin and norepinephrine levels in descending pain-inhibitory pathways may cause the allodynia and hyperalgesia of fibromyalgia.
Most studies of pharmacologic treatment of fibromyalgia have examined antidepressants for three reasons:
- There is evidence of the successful use of antidepressants in other chronic pain conditions.27
- These agents are effective for treating mood and anxiety disorders, which frequently occur in patients with fibromyalgia and may share a common physiologic abnormality. 28
- Antidepressants might enhance the activity of neurotransmitters such as serotonin and norepinephrine in the descending inhibitory pain pathways, leading to reduced pain perception.29
Tricyclics In randomized, controlled trials, tricyclic medications (including the muscle relaxant cyclobenzaprine) appear to be moderately effective in improving fibromyalgia symptoms. Two meta-analyses of trials of tricyclic medications (amitriptyline, dothiepin, cyclobenzaprine, clomipramine, and maprotiline) have found similar results.30,31 Our group found the greatest effect on measures of sleep improvement, which may be due in part to tricyclics’ sedative properties.30 Many patients with fibromyalgia, however, cannot tolerate the sedative and other side effects associated with tricyclic agents, even though low dosages (e.g., 25 mg/d of amitriptyline) have typically been used in clinical trials.
SSRIs. Selective serotonin reuptake inhibitors, although likely to be better tolerated than tricyclics, have been examined in only five placebo-controlled trials in fibromyalgia: two with citalopram, and three with fluoxetine. One citalopram study found no significant differences in efficacy between citalopram and a placebo,32 but the other reported significant improvement in one measure of pain and a significant decrease in depressive symptoms compared with the placebo group.33 No significant differences were found between groups in the global assessment of improvement.
The initial fluoxetine trial in fibromyalgia treatment did not reveal a significant therapeutic effect over a placebo,34 although the study was limited by a high (57%) placebo dropout rate, small sample size (42 subjects), brief duration (3 to 6 weeks after treatment), and restriction of fluoxetine dosage to 20 mg/d. In the two other controlled trials, including one which we recently conducted, fluoxetine was superior to a placebo in reducing pain and other fibromyalgia-associated symptoms.35,36
In our 12-week investigation (a randomized, placebocontrolled, parallel-group, flexible-dose trial), 60 subjects with fibromyalgia received fluoxetine 20 to 80 mg/d or a placebo.36 Those receiving fluoxetine (mean dosage 45 ±25 mg/d) displayed significantly greater reduction in pain, fatigue, and depression compared with those receiving the placebo. The effect of fluoxetine on pain remained significant after we adjusted for change in depression.
Sertraline was evaluated in an open study of 47 fibromyalgia patients at dosages of 25 to 200 mg/d for 6 weeks. Nearly two-thirds (63%) assessed the efficacy of sertraline as good or very good in the treatment of their symptoms.37 Paroxetine effectively reduced fibromyalgia symptoms in a single-blind study at dosages of 20 mg/d for 3 months.38
SNRIs Venlafaxine, a dual serotonin and norepinephrine reuptake inhibitor, has shown promise in the treatment of fibromyalgia in a preliminary open trial conducted by our group.39 Venlafaxine at a mean dosage of 167 mg/d resulted in significant improvement in fibromyalgia symptoms and quality of life compared with baseline. Notably, lifetime comorbid depressive and anxiety disorders were common in this sample, and their presence predicted response of fibromyalgia symptoms to venlafaxine.