Treatment of Pain in Bipolar Patients: Clinical Challenges
Pain problems are exceedingly prevalent among psychiatric patients. Clinical impression and neurobiological research suggest that physical and psychological aspects of pain are closely related. First, the neuroanatomical and functional overlap between pain and emotion/reward/motivation brain circuitry suggests integration and mutual modulation of these systems. Second, psychiatric disorders are commonly associated with alterations in pain processing, whereas chronic pain may impair emotional and neurocognitive functioning. Third, given its stressful nature, pain may serve as a functional probe for unraveling pathophysiologic mechanisms inherent in psychiatric morbidity. This review attempts to address the diagnosis and treatment of pain in one group of psychiatric patients—those with bipolar disorder.
Bipolar disorder is one of the 10 most debilitating illness worldwide, with a prevalence of 1.4%.1 The onset of bipolar disorder is usually between 15 and 30 years of age; the lifetime risk for bipolar is 5% to 10% for a first-degree relative. According to the National Institute of Mental Health, the lifetime prevalence of bipolar disorder is 3.9% of the US adult population (or approximately 9 million Americans).2
In comparison, up to 76.2 million American adults (26% of the adult population) experience chronic pain3:
- 28% experience low back pain
- 16% have severe headache or migraine pain
- 15% have neck pain
- 48 million Americans have arthritis4
The fifth edition of the Diagnostic and Statistical Manual of Mental Disorder has emphasized a need to translate research findings into a classification system for bipolar disorer.5 In general, bipolar disorder can be divided into four categories (see Table 1). Bipolar type I is characterized by the presence of episodes of mania and depression, and in particular is associated with a poor clinical and functional outcomes and a high suicide rate. One reason for the poor prognosis is the frequent misdiagnosis or late diagnosis of the disorder, leading to delay in the initiation of appropriate treatment.6 Indeed, although depression is a more common presentation than mania in individuals with bipolar disorder, bipolar depression continues to be frequently misdiagnosed and inappropriately treated as unipolar depression in individuals without a clear previous history of manic episodes.7
Signs and symptoms of mania include increased energy, excessively euphoric mood or extreme irritability, racing thoughts, increased rate of talking, sexual promiscuity, impaired judgment, and impulsivity. Bipolar type I has at least one manic episode, whereas type II has hypomania or subacute mania and at least one episode of major depression.
Pain and Bipolar Disorder
A number of researchers have linked bipolar disorder with chronic pain syndromes like fibromyalgia. University of Alabama researchers reported that 13% of fibromyalgia patients had bipolar disorder, a significant difference from the general population (P<0.001).8 Wilke et al of the Cleveland Clinic reported that 25% of patients with fibromyalgia have bipolar disorder.9 A study conducted at UCLA Cedars-Sinai Medical Center revealed that 10% of fibromyalgia consultations included patients with bipolar disorder, a 10- to 150-fold increase in prevalence of bipolar disorder.10 However, because the patients had little or no response to traditional fibromyalgia interventions, the investigators used the term pseudo-fibromyalgia to describe a form of chronic musculoskeletal pain in the bipolar population.10 Interestingly, substance P spinal fluid levels in bipolar patients are normal.11
International Headache Society criteria were used to study the prevalence of migraine in bipolar patients in New Zealand. The researchers found that the prevalence of migraine was 25.9% in the bipolar patients; 25% of bipolar men and 27% of bipolar women suffer from migraine.12 By contrast, the prevalence of migraine in the general population is 10.3%. In a Canadian study, men with bipolar disorder and migraine were likelier to receive welfare and social assistance than bipolar men without migraine. Women with both bipolar disorder and migraine were likelier to require help with personal or instrumental activities of daily living compared with bipolar women without migraine.13
In a National Institutes of Health study, the overall lifetime prevalence of migraine was 39.8% among patients with bipolar disorder.14 However, in a subgroup of patients with bipolar II disorder, the lifetime prevalence of migraine was 64.7%; the bipolar with migraine group was younger and tended to be more educated.14 One recent study has indicated that migraine in depressed patients is a bipolar spectrum trait.15 In a study of patients with affective disorder, those patients with comorbid migraine and affective disorder had a higher frequency of bipolar II disorder (43% vs. 10%), a lower frequency of bipolar I disorder (11% vs. 33%), an approximately equal frequency of unipolar depressive disorder (45% vs. 57%), and a higher frequency of affective temperaments (45% vs. 22%).16 The authors suggested that the presence of migraine may be used to delineate a distinct subgroup of the major affective disorders.
Functional neuroimaging studies reveal structural changes in amygdala and prefrontal cortex in the bipolar patient.17 Recent neuroimaging studies support the contention that bipolar depression, as well as pain distress and rejection distress, share the same neurobiological circuits. The study revealed an increase in headaches and chest pain during bipolar depression related to increased rejection sensitivity during depression. However, being rejection sensitive in general (ie, trait rejection sensitivity) did not predict pain during depression.18
Suicide Risk Increases With Pain Level
Both patients with chronic pain as well as patients with bipolar disorder are at increased risk for suicide. Although the majority of people with chronic pain do not develop suicidal tendencies, according to the National Pain Foundation, people with chronic pain other than arthritis are four times likelier to have attempted suicide than other adults.19 In fact, in one survey, 14% of respondents with three or more painful conditions said they had thought about suicide, and almost 6% reported an actual suicide attempt. Nearly 8% of people with frequent or severe headaches had thought about killing themselves. This is four times the rate found among adults with no chronic head pain.20
In a review of bipolar patients, a Duke University researcher found that 20% have attempted suicide.21 According to the study, suicide rates for bipolar patients are among the highest for any psychiatric disorder, and improved identification of risk factors for attempted and completed suicide translates into improved clinical outcome.