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Psychiatric Disorders and Risk of Transition to Chronicity in Men with First Onset Low Back Pain

William S. Shaw PhD, Adrienne J. Means-Christensen PhD, Mark A. Slater PhD, John S. Webster MD, Thomas L. Patterson PhD, Igor Grant MD, Steven R. Garfin MD, Dennis R. Wahlgren MA, Shetal Patel PhD, J. Hampton Atkinson MD
DOI: http://dx.doi.org/10.1111/j.1526-4637.2010.00934.x 1391-1400 First published online: 1 September 2010

Abstract

Objective. To assess whether pre-existing psychiatric diagnoses increase the likelihood of transitioning from sub-acute to chronic back pain.

Design. Prospective cohort study.

Methods. Men (N = 140) experiencing a first onset of low back pain (LBP) were examined for lifetime psychiatric disorders approximately 8 weeks post pain-onset using the Diagnostic Interview Schedule (DIS-III-R), then re-evaluated at 6 months after pain onset to determine who did or did not progress to pain chronicity.

Outcome Measure. Transition to chronic pain and disability was based on 6-month self-report measures of pain intensity and perceived disability.

Results. Men with a pre-pain lifetime diagnosis of major depressive disorder had 5 times greater risk of transitioning to chronic LBP (odds ratio [OR] = 4.99; 95% confidence interval [CI] 1.49–16.76). Increased risk was also associated with a pre-pain lifetime diagnosis of generalized anxiety (OR = 2.45; 95% CI 1.06–5.68), post-traumatic stress (OR = 3.23; 95% CI 1.11–9.44), and with current nicotine dependence (OR = 2.49; 95% CI 1.15–5.40). There were no statistically significant effects for abuse or dependence of alcohol or other psychoactive substances.

Discussion. Lifetime history of major depression or a major anxiety disorder may represent potential psychosocial “yellow flags” for the transition to chronicity in men with first-onset LBP. Screening for lifetime depressive or anxiety disorders may identify individuals at higher risk, who may benefit from referral for more intensive rehabilitation.

  • Chronic Low Back Pain
  • Disability
  • Psychiatric Disorders
  • Depression
  • Prognosis

Introduction

Psychological factors are thought to play a significant role in the onset of chronic pain [1] and the transition from sub-acute to chronic low back pain (LBP) [2–4]. Reviews of prospective cohort studies have concluded that there is increased risk of transition to chronicity when psychological “yellow flags” (emotional distress, depressed mood, and somatization) are present but have noted limitations in study design and measurement that weaken the strength and precision of these findings, and there has been a call for more high quality evidence [3,4]. Specifically, most research has been limited to individuals with recurrent or persisting pain problems rather than first onset back pain. Recall bias is inherent in retrospective studies of patients with longstanding back pain, making it difficult to determine whether distress is a prelude or consequence of pain. Additionally, use of mood symptom scales, rather than psychodiagnostic assessment, makes it difficult to distinguish between the emotional distress, discouragement associated with pain, depressive symptoms, depressed mood, and psychiatric disorders [3–5].

Recent prospective psychiatric epidemiological studies suggest that a current diagnosis of major depressive disorder at study entry predicts both recurrent [6] and new onset [7] complaints of LBP at follow-up ranging from 2 to 13 years. This suggests that history of mood disorder, and thus perhaps other psychiatric disorders, might enhance vulnerability to transition to chronic back pain. If so, detection of increased risk might be possible at an early phase of pain evaluation, and early treatment might reduce risk of developing chronic pain.

In an effort to further address this question, we examined data from a cohort of men with first lifetime episode of LBP, who underwent a research assessment after pain had persisted 6–10 weeks. They were then re-examined 6 months after the date of first pain onset to determine who did or did not transition to chronicity. The first onset of back pain was studied, since the risk of chronicity increases with recurrent back pain [8–11], making it difficult to disentangle the timing and the effects of medical and psychiatric disorder. It is possible that the burden of recurrent pain episodes over time is associated with subsequent onset of psychiatric disorder, which then increases the risk of a transition to persisting pain. Alternatively, a history of psychiatric disorder might enhance vulnerability to chronic pain even in first-onset cases.

To control for the possible effects of co-morbid medical conditions on everyday function, we excluded individuals with chronic medical illnesses. To add details beyond that of population-based research, which must rely only on symptoms to identify back pain cases, the present study reports on data based on standardized orthopedic examination. Finally, we considered a range of major psychiatric disorders apart from mood disorder, diagnosed using structured psycho-diagnostic evaluations. The primary research goals were to: 1) determine the lifetime frequency of pre-pain psychiatric disorders; 2) distinguish current from past psychiatric diagnoses; and 3) test the association between pre-existing psychiatric disorders and the transition from sub-acute to chronic pain. We hypothesized that the presence of pre-existing major depression and substance use disorders would increase the likelihood of transition to chronic pain (i.e., pain on a daily basis for 6 months).

Methods

Data were collected as part of a research program intended to address risk of progression from early to chronic back pain, and interventions to prevent this transition. All participants were men attending an orthopedic clinic in a closed health care system (Naval Medical Center, San Diego, CA, between 1992 and 1994). In this system, health care and disability benefits were not dependent on classification of back injuries as either work-related or not work-related, and in either instance, evaluation and treatment would be similar. Participants received the usual orthopedic care [12] throughout the study, as described later. Baseline research evaluations were conducted at a point when the patient qualified for and was enrolled in the research (i.e., when the person had first onset daily pain lasting at least 6 weeks but no more than 10 weeks). At a second point 6 months after back pain commenced, the assessments were repeated to determine if pain had transitioned to chronicity. For practical reasons, this study design was a compromise. The ideal design would randomly select individuals from the population, and then follow them for onset and course of LBP. Alternatively, one could follow all individuals presenting to clinic with acute first-onset pain. Such approaches are costly, given the high rates of resolution of first-onset LBP. Consequently, we required potential research participants to have first-onset LBP for at least 6 weeks but no more than 10 weeks at the time of enrolment and baseline evaluation, since patients with subacute pain are more likely to transition to chronicity. The study was approved by the Institutional Review Board of the University of California, San Diego, and the Scientific Review Committee, Naval Medical Center, San Diego. All participants gave written informed consent before enrolling.

Participants

Patients with first onset back pain were tracked by their providers from the point of entry into the clinic to the point where first onset LBP had persisted for at least 6 weeks, but less than 10 weeks. They were then informed of their potential eligibility for the study. Inclusion criteria were 1) age between 18 and 50 years (to reduce risk of recruiting older individuals with advanced degenerative disease, like spinal stenosis); 2) experiencing first episode of low (T-6 or below) back pain; and 3) pain present on a daily basis for between 6 and 10 weeks. Exclusion criteria were 1) major medical illness (e.g., insulin-dependent diabetes, chronic obstructive pulmonary disease) or co-occurring pain disorder that would have confounded assessment of impact of back pain on everyday function; 2) being unavailable for the face-to-face follow-up assessment (e.g., anticipated to be transferred out of the area); 3) prior episode of back pain on a daily basis lasting 1 week or longer; 4) taking medications known to affect mood (e.g., antidepressants, anxiolytics); 5) major surgery in the prior 12 months (which would confound assessment of pain and function; or 6) back pain as a result of neoplastic disease, osteomyelitis, or fracture, since the course of illness would differ from typical injury-related or mechanical back pain.

Of 148 men identified as potential participants, a total of 140 men enrolled and completed the baseline assessment. Eight eligible patients declined to participate. One hundred twenty-two participants completed the follow-up at 6 months post pain onset. Chi-square analyses and t-tests comparing eight demographic and clinical baseline characteristics for those who did and did not complete 6 months follow-up revealed that dropouts tended to be younger (24.46 vs 30.40; t[138] = 2.93, P < 0.01) and unmarried (61.5% vs 32.2%; χ2[1] = 4.44, P < 0.05). There were no significant differences with regard to ethnicity, education, income, mood, pain intensity, or everyday function.

In terms of demographic and clinical characteristics, the average age was 30 years (SD = 7.19); 65% were married, 29% were single, and 6% were divorced or separated. The sample was 66% Caucasian, 16% African American, 7% Hispanic, 4% Asian, 3% Native American, and 3% “other”. Seventy-nine percent of participants had a high school diploma or equivalent, 10% had an associate or a 2-year technical degree, and 10% had a bachelor's degree or more. Using the nomenclature of the Quebec Task Force on Spine Disorders [13], 46% (N = 64) were classified as back pain without radiation, 24% (N = 33) had pain with proximal (above the knee) radiation, 15% (N = 21) had pain with distal (below the knee) radiation, and 16% (N = 22) had neurological signs (weakness, or reflex or sensory abnormality).

The orthopedic clinic followed standard Agency for Healthcare Policy and Research guidelines for evaluation and treatment of acute back pain [14], consisting of an orthopedic examination, education about back pain (e.g., its typical resolution within 1–2 weeks), and as appropriate recommendations for general health maintenance (e.g., exercise, weight reduction, smoking cessation). Non-steroidal anti-inflammatory medications (NSAIDs) were offered as needed; opioid analgesics and muscle relaxants generally were not prescribed, in line with the usual approach to “mechanical” LBP. Return visits were offered on a walk-in basis if symptoms persisted. Participants enrolled in the study were seen in the follow-up orthopedic clinic an average of two visits over the course of the study. None were prescribed psychotropic medications (e.g., antidepressants; anxiolytics). Results of the psychiatric research assessments were discussed with the participant.

Procedure

Qualified patients who agreed to participate in the study completed a standardized orthopedic evaluation, conducted by an orthopedic physician and nurse practitioner. A psychology technician blind to the hypothesis completed a structured psychodiagnostic interview and evaluations of pain intensity, disability, and distress. On average, baseline assessment took place approximately 2 months following pain onset; the assessments were repeated at 6 and 12 months post pain onset (see Figure 1).

Figure 1

Timeline of subject recruitment and data collection.

Measures

Psychiatric Diagnoses

The Diagnostic Interview Schedule Version III-R (DIS) [15] was used to provide psychiatric diagnoses. The DIS is a fully structured psychiatric interview, administered by a trained lay interviewer, which yields lifetime and recent psychiatric diagnoses based on DSM-III-R criteria [16]. The diagnoses included in the present study were major depression, dysthymia, bipolar disorder, panic disorder, generalized anxiety disorder, somatization disorder, alcohol abuse, alcohol dependence, post-traumatic stress disorder (PTSD), psychoactive substance abuse and dependence, schizophrenia and schizoaffective disorder, and antisocial personality disorder. Diagnoses were recorded without reference to hierarchical exclusion criteria. This DIS records age of onset and offset for each disorder, and the recency when symptoms of the disorder were last experienced (i.e., within the last 2 weeks, last month, last 6 months, last 6–12 months, or more than 12 months ago). These data were used to time the onset and course of psychiatric disorder relative to data gathered separately on the patient's orthopedic and pain history (e.g., date of pain onset). Validity and reliability data for the DIS are acceptable to good and agreement with blinded clinically established diagnoses ranges from 0.7 to 0.9 for most conditions [17].

Pain Intensity

The Descriptor Differential Scale (DDS) [18] is a self-report paper-and-pencil questionnaire, in which the respondent rates the intensity and unpleasantness of their pain relative to verbal descriptors of pain. There are 12 intensity descriptors (e.g., faint, moderate, extremely intense) and 12 unpleasantness descriptors (e.g., slightly unpleasant, distressing, annoying). Patients place a check mark on a dashed line with 10 positions anchored by “less than” and “more than.” Patients' pain ratings relative to each of the 12 descriptors are averaged within each dimension of pain (intensity and unpleasantness). The DDS has been shown to be a valid measure of pain across clinical and experimental samples [19].

Disability in Everyday Function

The Sickness Impact Profile (SIP) [20] is a 136-item self-report measure that provides an evaluation of the interference of pain in daily activities. It assesses 12 discrete areas of disability, with summary scores of physical impairment, psychosocial difficulty, and overall impact of pain. Scores reflect the patient's degree of impairment, ranging from 0 to 100%. For this study, scores were computed for overall impairment, which is the weighted mean of physical, psychosocial, and other impairment subscale scores. Reliability and validity are acceptable [20] and the SIP has been validated for use among patients with LBP [21].

Chronic Pain

The clinical outcome of chronic pain was defined according to a previously reported classification system [22], which categorizes back pain patients as chronic if cut-points are exceeded on standardized measures of pain intensity (DDS), disability in everyday function (SIP), and depressed mood (Beck Depression Inventory). However, to eliminate the potential confound of a mood measure in our chronic pain definition, the depressed mood criterion was dropped for the current analyses. Thus, participants were categorized as having chronic pain at 6-month follow-up if the SIP score was greater than 10 (indicating at least mild disability) and the DDS score for pain intensity was greater than 10 (the scale mid-point and a typical score for patients seeking treatment for chronic pain in tertiary care centers). Others, whose scores on one or both measures were below the cut-points were considered “remitted.”

Statistical Analyses

Descriptive statistics were used to report percentages of patients in each category of clinical status and prevalence of DSM psychiatric diagnoses at baseline. Chi-square analyses were used to determine differences between remitted and chronic pain groups on baseline rates of psychiatric disorders. For significant chi-square analyses, odds ratios (with 95% confidence intervals) for progression to chronic pain based on baseline diagnoses were computed. Standard power analyses indicated that a sample size N = 150 would be adequate to test the hypothesis that psychiatric disorder would be associated with transition to chronic pain [23]. The analyses were based on three assumptions derived from the literature. First, surveys suggested a 50% prevalence of pre-pain lifetime psychiatric disorder in patients with chronic back pain [24]. Second, epidemiologic studies of men in the sample's expected age range estimated a lifetime prevalence for the psychiatric disorders of interest to be less than 20% [25]; and studies of men with acute back pain suggested rates are in line with community samples [26,27]. Third, research suggests that up to 50% of individuals whose back pain has persisted into the sub-acute phase will continue to have pain at six months after onset [2,28]. Assuming patients who transition to chronicity would have rates of psychopathology similar to the typical “chronic” back pain patient, and those whose pain resolves will have rates of psychopathology similar to community controls, the power of the design (i.e., N1 = 75; N2 = 75) was greater than 0.95. No statistical adjustment was made for potential demographic confounders, as the sample was rather homogeneous with regard to age, employer, access to health care and insurance benefits, general fitness, social environment, and organizational culture. While we considered possible inclusion of income and education as covariates, the small sample size and restricted range prevented any useful multivariate adjustments or stratification of results.

Results

Frequency of Psychiatric Diagnoses

Excluding nicotine dependence, a lifetime history of at least one DSM III-R psychiatric disorder was present for 59% (N = 83) of patients (Table 1). Approximately 32% (N = 45) of patients had two or more lifetime disorders and 16% (N = 22) had three or more disorders. The most frequent lifetime disorders were alcohol abuse and dependence, other substance use disorders, and major depression. For rough comparison, Table 1 also describes rates reported in a national population-based study of the community for comparably aged men (the National Co-morbidity Survey, ages 18–54 years) [25], and archival data from an earlier DIS study at this institution addressing the frequency of psychiatric disorder in a chronic back pain sample [24]. In general, it appears that sub-acute patients are not as likely to have psychiatric disorders as are patients seeking treatment for chronic back pain.

View this table:
Table 1

Lifetime and recent DSM III-R diagnoses at baseline assessment (6–12 weeks post onset of pain)

Psychiatric diagnosesStudy sampleComparison groups
Sub-acute low back pain (N = 140) (%)National Comorbidity Survey (N = 8,098) (%)Orthopedic patients with chronic low back pain (N = 97) (%)
Major depression
Lifetime11.412.732.0
Past 12 months3.67.721.6
Dysthymia§0.74.823.7
Generalized anxiety disorder
Lifetime4.33.622.7
Past 12 months0.02.013.4
Panic disorder
Lifetime0.72.08.2
Past 12 months0.01.37.2
Somatization disorder
Lifetime0.0N/a0
Past 12 months0.0N/a0
Alcohol abuse or dependence
Lifetime51.432.664.9
Past 12 months15.014.112.4
Other substance use disorder
Lifetime21.414.611.3
Past 12 months1.45.24.1
Post-traumatic stress disorder
Lifetime22.114.611.3
Past 12 months2.15.24.1
Anti-social personality disorder§6.45.821.6
  • Diagnoses for the present study and National Comorbidity Survey (NCS) diagnoses are DSM-III-R diagnoses. NCS data provide United States population prevalence estimates for men ages 15–54. Lifetime and 12-month diagnostic rates include patients with a current diagnosis.

  • Chronic low back pain diagnoses from Atkinson et al. [1991] are DSM-III diagnoses; rates are for lifetime and six month periods.

  • § The Diagnostic Interview Schedule does not reference this diagnosis to a specific period.

To understand whether psychiatric morbidity might be a near antecedent or consequence of back pain, we studied the prevalence of DIS-determined conditions in the 6-months preceding baseline evaluation. Here, 24 percent (N = 34) had at least one disorder meeting criteria within the 6 months preceding the research assessment (excluding nicotine dependence). Again, alcohol use disorder was the most prevalent recent disorder. Of the 34 patients with psychiatric diagnoses in the 6 months before baseline, all diagnoses preceded the onset of pain by more than a year.

Psychiatric Disorders and Transition to Chronic Pain

To determine whether lifetime or recent (within last 6 months) psychiatric disorders increased the likelihood of transition to chronic pain, we examined the psychiatric history in patients (N = 49, 40%) who met our definition of chronicity (DDS pain intensity > 10; SIP disability > 10) at 6-months following pain onset compared with patients (N = 73, 60%) whose back pain problem was considered clinically “remitted” (scores on at least one measure below the cut scores above). The results are shown in Table 2. Relative to patients with no history of major depression, patients with a lifetime history of major depression were five times more likely to be categorized as “chronic pain” 6 months after pain onset. A lifetime history of generalized anxiety disorder was associated with a 2.5-fold increased risk of chronic pain, and a history of PTSD with a 3.2-fold increase in risk. Current nicotine dependence was also associated with a 2.5-fold increased risk of chronic pain. There were no associations for alcohol or other psychoactive substance abuse or dependence to increase risk of chronic pain (P > 0.05).

View this table:
Table 2

Odds ratios of transition to chronic pain based on pre-existing DSM-III-R psychiatric disorders

Diagnostic categoryYes/noFrequency of transition to chronic disabling pain (>6 months)Statistic
NN%χ2 (df = 1)OR95% CI
Major depression (lifetime)
No1073835.57.76**1.00(1.49–16.76)
Yes151173.34.99
Major depression (by recency)
No lifetime diagnosis1074539.19.56**1.00(0.51–11.39)
Past 6 months7457.12.42
>6 months8787.512.71(1.51–107.21)
Generalized anxiety (lifetime)
No923234.84.44*1.00(1.06–5.68)
Yes301756.72.45
Generalized anxiety (by recency)
No lifetime diagnosis923234.86.81*1.00(1.36–16.14)
Past 6 months141071.44.69
>6 months16743.81.46(0.50–4.28)
Alcohol dependence (lifetime)
No762938.2NS1.00(0.59–2.62)
Yes462043.51.25
Alcohol dependence (past 6 months)§
No1104339.1NS1.00(0.47–5.15)
Yes12650.01.56
Alcohol abuse or dependence (lifetime)
No612236.1NS1.00(0.68–2.91)
Yes612744.31.41
Alcohol abuse or dependence (past 6 months)
No1064138.7NS1.00(0.55–4.55)
Yes16850.01.59
Psychoactive substance dependence (lifetime)
No1024140.2NS1.00(0.41–2.97)
Yes19842.11.10
Psychoactive substance dependence (past 6 months)
No1204840.0NS1.00
Yes11100.02.46
Psychoactive substance abuse or dependence (lifetime)
No973839.2NS1.00(0.50–2.97)
Yes251144.01.22
Psychoactive substance abuse or dependence (past 6 months)
No1214840.0NS1.00
Yes11100.02.46
Nicotine dependence (lifetime)
No642437.5NS1.00(0.61–2.61)
Yes582543.11.26
Nicotine dependence (past 6 months)
No822732.95.40*1.00(1.15–5.40)
Yes402255.02.49
Antisocial personality disorder (lifetime)
No1134338.1NS1.00(0.77–13.70)
Yes9666.73.26
Post-traumatic stress disorder (lifetime)
No1053836.24.86*1.00(1.11–9.44)
Yes171164.73.23
Psychiatric co-morbidity (lifetime)
No diagnosis451226.76.22*1.00(0.80–5.03)
One diagnosis381642.12.00
More than one diagnosis392153.83.21(1.29–7.99)
Psychiatric co-morbidity (past 6 months)
No diagnosis933133.38.01*1.00(0.88–7.56)
One diagnosis16956.32.57
More than one diagnosis15969.24.50(1.28–15.77)
  • Chronic disabling pain defined by sickness impact profile score > 10 and/or pain intensity DDS score > 10.

  • Insufficient group size for confidence interval computation.

  • * P < 0.05;

  • ** P < 0.01.

To determine whether a more recent diagnosis of a mood disorder might have a greater effect, we stratified analyses by groups according to whether diagnoses were present within the last 6 months) or more remote (recency > 6 months prior to baseline assessment). For generalized anxiety, the trend was in the hypothesized direction, with more recent (within last 6 months) anxiety diagnoses showing a larger effect (OR = 4.69 vs 1.56), though these effects had overlapping confidence bands and thus not statistically different. For major depression, however, the trend was in the opposing direction, with more remote (>6 months ago) diagnoses having a larger impact (OR = 12.71 vs 2.42), but again with overlapping confidence bands.

To determine whether having multiple psychiatric diagnoses might further increase the risk of transition to chronic pain, patients were stratified into three groups (no diagnoses, one diagnosis, more than one diagnosis) for both lifetime and current psychiatric diagnoses. Because nicotine dependence was so prevalent, it was not included in this stratification. Four patients had a lifetime history of all five psychiatric categories (depression, anxiety, PTSD, alcohol abuse, and substance abuse), 6 had four lifetime diagnoses, 12 had three lifetime diagnoses and 23 had two lifetime disorders. The analysis of multiple lifetime diagnoses showed an increase in the odds ratio for chronicity of pain (3.21 vs 2.00), but overlapping confidence bands did not show that these were statistically significant differences. Similarly, an analysis of individuals with multiple recent (6 month) diagnoses (N = 15) showed no statistically significant increase in the chronicity of pain (P > 0.05).

Discussion

Past research has linked psychiatric disorders to the development and maintenance of chronic back pain syndromes, but most of this evidence is taken from retrospective studies among patients with a longstanding chronic pain problem. Recent prospective, population-based research has addressed this issue by identifying individuals without chronic back pain at entry, and relating onset or recurrence of pain to major depressive disorder [6,7]. It is not altogether clear from such research whether back complaints are strictly “chronic” (pain on a daily basis for 6 months or more), are the result of back injury or spine disease, or if they might be a reflection of somatic symptoms of depression. Pain complaints, particularly headache and backache, are prevalent during episodes of major depression and resolve as depression remits. Further, individuals with recurrent back episodes usually are the majority of cases, and individuals with recurrent pain are at higher risk for chronicity and emotional distress [4]. The present study adds detail and specificity to the relationship between psychopathology and persistence of pain by recruiting a cohort shortly after a first onset of back pain, conducting standardized orthopedic, psychodiagnostic assessments, and following patients for 6-month outcome based on rigorous operationalized criteria. In studying first onset rather than recurrent cases we aimed to more clearly understand the relationship of pain and psychiatric disorder. Our two major findings are that 1) patients with sub-acute LBP had a lifetime and 12-month frequency of major depression, major anxiety disorders, and non-alcohol substance use disorders lower than that observed in patients with chronic LBP as might be expected, based on the impact of chronic pain on mental health; and 2) risk of transition to chronic pain was significantly elevated in the presence of a lifetime diagnosis of major depression, PTSD, and generalized anxiety, or a diagnosis of nicotine dependence in the past 6 months.

One previous study that most directly compares with our baseline psychiatric data involved patients evaluated at an occupational health center within 4 weeks of back pain injury [26]. Overall, the lifetime rates of psychopathology in that sample were also lower than the rates in chronic LBP [24,26,28]. Furthermore, our study supports results from prior population-based research using comparable, structured psychodiagnostic instruments, which indicated that antecedent major depressive disorder was associated with reports of chronic back pain (daily pain for ≥6 months) or “having a lot of trouble with back pain” over intermediate (2-year) and very long-term (13-year) follow-up [6,7]. An epidemiologic study also reported that another mood syndrome, bipolar mood disorder, is associated with a significantly elevated risk of reporting marked pain interference in everyday life [29]. This suggests that bipolar disorder might also confer risk of progressing to chronic pain disability in patients with acute or subacute back pain.

The majority of studies in chronic musculoskeletal pain support the hypothesis that over time, depressive disorders are more likely to be a consequence than an antecedent of persisting pain [5]. However, the present data may support an antecedent effect of major depression and anxiety disorders on pain as well. Most studies arguing against the antecedent hypothesis have not used standardized psychodiagnostic evaluation for major depressive disorder, relying instead on depressive symptom scales, which are insufficient for diagnosis [5]. Two studies using rigorous psychiatric diagnostic instruments noted that 40 to 50% of chronic back pain patients with a lifetime history of major depression reported that the onset of the depressive symptoms preceded chronic pain [24,26]. In those who progressed to chronic pain in the present study, the lifetime prevalence of pre-pain major depression exceeded 20%, which is consistent with the above observations. Recent research in community elderly populations suggests that depression symptoms at baseline are predictive of subsequent complaints of disabling LBP [9]. Anxiety disorders, which also impacted outcome, are less well studied in chronic pain research, but there is evidence of elevated rates of PTSD in patients with persisting pain [30], although in much of this literature PTSD is a response to an injury-event which also is the source of chronic pain.

Somewhat surprising was the lack of relationship between alcohol or other substance abuse and progression to chronic pain status, especially considering the elevated prevalence of these diagnoses in some chronic back pain samples [24,26,31], and evidence that in the majority of cases the alcohol use disorder preceded pain onset [24,26]. We have no ready explanation for this.

Cigarette smoking has been a weak, but consistent prognostic indicator for LBP recovery in a number of prospective studies [32,33], and results of the current study provide further support, with a 2.5-fold increase in transition to chronic pain among those with a current nicotine addiction. More research is needed to determine whether effects of smoking on back disability are mediated by physiological mechanisms, or whether this is simply a representative marker for negative health behaviors. In most studies to date, the effect of smoking on LBP outcomes has persisted even after controlling for other general health indicators, so this consistent effect has not been easily explained by potentially confounding factors.

A “diathesis-stress” model has been proposed as a link between psychiatric disorder and chronic pain [34]. In this model, pre-pain psychopathology is a diathesis heightening vulnerability to developing chronic pain after acute injury [34]. Recent neurobiologic research is beginning to develop mechanistic insights into this process. Functional neuroimaging suggest for example that major depression is associated with a maladaptive, decreased activation of a neural network involved in endogenous pain and emotional modulation [1]. This “ineffective” response of anterior cingulate and pre-frontal cortical structures to pain modulation and a heightened anticipation of negative events (i.e., pain) may bias individuals toward helpless and depressed mood [1]. Likewise there is evidence of abnormal pain processing and a negative affective bias in PTSD [35]. Our data, suggesting that a history of major depression or anxiety disorder increases risk of transition to chronicity, is consistent with this model.

The study has several methodological limitations. The sample size is small, as reflected in wide confidence intervals around estimated odds ratios, so it was possible only to address the most frequent psychiatric disorders. A larger sample would be needed to determine risk attributable to disorders of low population prevalence. The generalizability of results is limited because the sample was exclusively male and recruited from a military clinic. Nevertheless, the age range and socioeconomic standing of the sample is consonant with the demographic characteristics of a large proportion of the population at risk for chronic LBP [28]. Restriction of the study sample to first-time back pain patients free of other serious or chronic disabling illnesses provided a unique opportunity to study the early clinical course of LBP before any long-term suffering, exposure to multiple therapies and diagnostics, repeated treatment failures, or workers' compensation, all factors that pose a serious problem of (“chicken or egg”) circularity [36] when studying the prognostic importance of psychiatric status. This improved the internal validity of the study by eliminating many of the possible confounders that would exist in a clinic population with exposure to varying levels of experience with pain and pain treatment. On the other hand, this design limited the external validity of study results, by making it more difficult to generalize to broader patient populations. Next, our approach to outcome classification, while standardized, is only one of many possible methods [37,38]. In addition, the results do not address the question of longer-term outcome, and it is unclear if the men we classified as “chronic” are launched on a years-long career of pain and disability. Some research suggests the majority of back pain patients whose symptoms persist for more than 2 to 4 months continue to have pain and disability one year after seeking care [2,10,39]. Finally, other psychosocial factors (pain beliefs, workplace concerns, social support, self-perception of disability) that were not included in these analyses may also affect transition to chronicity [40].

It has been recommended that future research on transition to chronicity focus on validated instruments measuring factors amenable to clinical intervention [3], such as psychiatric disorder. Indeed, a very brief 4-question screener is available to efficiently assess for presence of a history of major depression and anxiety (e.g., Patient Health Questionnaire-4) [41]. If research confirms that selected disorders predict risk for persisting difficulty, at least in sub-acute back pain, such brief assessments might be easily applied in clinical settings. If so, then affected individuals might be readily identified for more intensive follow-up or rehabilitation efforts.

Acknowledgments

The authors wish to thank JoAnn Grant RN, Lauren Gosewisch NP, Pat Bone RN, Nann Epler, Judy Ortega and Jo Anne Epping-Jordan PhD for their participation in the data collection and management for this project. Supported by the US Department of Veterans Affairs, and by a Young Investigator Award to Dr Means-Christensen from NARSAD: The Mental Health Research Association.

The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Navy, the Department of Defense, or the United States Government. The voluntary informed consent of the participants used in this research was obtained as required by SECNAVINST 3900.39B. The Chief, Bureau of Medicine and Surgery, Navy Department, Washington, DC, Clinical Investigation Program sponsored this report as required by HSETCINST 6000.41A.

References

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