Abstract
Context: Little is known about the role that cytokines play in osteopathic manual treatment (OMT) of patients with chronic low back pain (LBP).
Objective: To measure the baseline concentrations of interleukin (IL)-1β, IL-6, IL-8, IL-10, and tumor necrosis factor (TNF)-α in patients with chronic LBP; the correlations of these cytokine concentrations with clinical measures, including the number of key osteopathic lesions; the changes in cytokine concentrations with OMT; and the association of such changes with clinical outcomes.
Design: Substudy nested within a randomized controlled trial of OMT for nonspecific chronic LBP.
Setting: University-based study in Dallas-Fort Worth, Texas.
Patients: Seventy adult research patients with nonspecific chronic LBP.
Main Outcome Measures: A 10-cm visual analog scale, the Roland-Morris Disability Questionnaire, and the Medical Outcomes Study Short Form-36 Health Survey were used to measure LBP severity, back-specific functioning, and general health, respectively.
Results:At baseline, IL-1β (ρ=0.33; P=.005) and IL-6 (ρ=0.32; P=.006) were each correlated with the number of key osteopathic lesions; however, only IL-6 was correlated with LBP severity (ρ=0.28; P=.02). There was a significantly greater reduction of TNF-α concentration after 12 weeks in patients who received OMT compared with patients who received sham OMT (Mann-Whitney U=251.5; P=.03). Significant associations were found between OMT and a reduced TNF-α concentration response at week 12 among patients who achieved moderate (response ratio, 2.13; 95% confidence interval [CI], 1.11-4.06; P=.006) and substantial (response ratio, 2.13; 95% CI, 1.07-4.25; P=.01) LBP improvements, and improvement in back-specific functioning (response ratio, 1.68; 95% CI, 1.04-2.71; P=.03).
Conclusions: This study found associations between IL-1β and IL-6 concentrations and the number of key osteopathic lesions and between IL-6 and LBP severity at baseline. However, only TNF-α concentration changed significantly after 12 weeks in response to OMT. These discordant findings indicate that additional research is needed to elucidate the underlying mechanisms of action of OMT in patients with nonspecific chronic LBP.
Osteopathic manual treatment (OMT) is commonly used for a variety of musculoskeletal conditions, including low back pain (LBP). A systematic review and meta-analysis of 6 randomized controlled trials
1-6 demonstrated that OMT significantly reduced low back pain.
7 Subsequently, these findings led to the development and publication of the first and only clinical practice guideline established by the American Osteopathic Association.
8 This guideline, which has been accepted by the Agency for Healthcare Research and Quality for posting on its National Guideline Clearinghouse,
9 recommends that osteopathic physicians use OMT in the care of patients with LBP.
During the past decade, a small, emerging body of research has explored biomarker response to OMT for a variety of musculoskeletal conditions. Investigations have included nitric oxide response in blood and vasculature following fluidic motions “comparable to manipulations”
10; cytokine and growth factor responses to in vitro modeling of repetitive motion (strain) injuries and “modeled OMT”
11-14; endocannabinoid responses in healthy volunteers subjected to OMT
15; and various biomarker responses in a pilot study of OMT administered to participants with and without chronic LBP.
16 Nevertheless, the American Osteopathic Association guideline recommends further research to elucidate mechanistically how OMT exerts its effects in patients with LBP.
8 The present study, nested within the OSTEOPAThic Health outcomes In Chronic low back pain (OSTEOPATHIC) Trial,
17 assesses the associations of cytokine concentrations with somatic dysfunction, LBP severity, back-specific functioning, and general health, and further explores cytokine responses to OMT in patients with chronic LBP.
Each patient in this study agreed to have blood drawn from an antecubital vein for cytokine measurements, including interleukin (IL)-1β, IL-6, IL-8, IL-10, and tumor necrosis factor (TNF)-α. The pre- and posttreatment blood samples were taken 30 minutes prior to the first treatment session and at the week 12 exit visit, which occurred 4 weeks after the last treatment session. The venous blood was centrifuged at 1200g for 15 minutes at 4 °C. Serum samples were then aliquoted and stored at −20 °C for analysis. Serum samples were either analyzed unconcentrated or concentrated prior to testing using Centriprep centrifugal filter units with YM-3 3000 MW filters (EMD Millipore, Billerica, Massachusetts).
Cytokine concentrations were measured using the commercially available Milliplex MAP human cytokine kit (EMD Millipore, Billerica, Massachusetts). Briefly, 25 μL of serum, standard, or control were added to the appropriate wells. Then, 25 μL of the mixed or premixed cytokine assay beads were added to each well. Plates were sealed and incubated on a plate shaker overnight at 4 °C. Then, plates were washed 2 times with 200 μL/well of wash buffer, and 25 μL of detection antibodies was added to each well. Plates were sealed and incubated on a plate shaker for 1 hour at room temperature (20° to 25°C). Then, 25 μL of streptavidin-phycoerythrin conjugate was added to each well containing the 25 μL of detection antibodies, and plates were sealed and incubated on a plate shaker for 30 minutes at room temperature (20° to 25°C). Plates were washed 2 times with 200 μL/well of wash buffer, and 150 μL of sheath fluid was added to all wells. The assay beads were resuspended on a plate shaker for 5 minutes. Plates were run on the Bio-Plex 100 System (Bio-Rad Life Science Research, Hercules, California). The Bio-Plex Manager software was used to determine cytokine concentrations from relative median fluorescent intensity (RMFI) responses, using linear or 5-parameter logistic curve-fitting methods. Concentrations were determined from the cytokine standard curves extrapolated to 0 RMFI. Cytokine concentrations determined to be at or below 0 pg/mL were recorded as 0 pg/mL.
To our knowledge, the present study is the first to explore the associations of cytokine concentrations with baseline somatic dysfunction and outcomes in a clinical trial of OMT. This setting enables a more conventional and realistic assessment of the role of cytokines in mediating response to OMT than previous studies, which either used laboratory-simulated OMT
10-14 or studied OMT in healthy participants.
15,16 There were 3 advantages of nesting this study within the OSTEOPATHIC Trial. First, because it has already been shown that OMT is efficacious in reducing LBP,
7,8 the likelihood of finding valid and statistically significant associations of cytokine concentrations with OMT was enhanced. Second, the randomization of patients to OMT or sham OMT within the OSTEOPATHIC Trial minimized the possibility that confounders, known or unknown, might distort the relationships among cytokine concentrations, OMT, and clinical outcomes. Third, the algorithmic approach to OMT provision in the OSTEOPATHIC Trial
17 facilitates future replication of our study findings.
The most highly significant pairwise correlations among baseline cytokine concentrations (IL-1β/IL-6; IL-6/IL-10; and IL-8/TNF-α) that we observed in our patients with chronic LBP were consistent with correlations of cytokine concentration reported in asymptomatic persons.
30 There were significant correlations between the concentrations of both IL-1β and IL-6 and severe somatic dysfunction, as manifested by the presence of key osteopathic lesions. Additionally, IL-6 concentration was correlated to a lesser degree with LBP severity. However, the only change in cytokine concentration after 12 weeks that was associated with OMT was a reduction in TNF-α. This change was most evident in patients who achieved clinical responses, as manifested by improvements in LBP severity and back-specific functioning. Thus, the discordant findings for cytokine concentrations and their associations with key osteopathic lesions, LBP severity, and OMT raise additional questions for future research.
The pathophysiology of LBP has been studied in patients with intervertebral disk degeneration and herniation. Although the relationship between disk degeneration and LBP is not clearly understood, it appears that IL-1 and TNF-α may be responsible for local chemical mediation of pain by promoting matrix degradation by means of enhanced production of matrix metalloproteinases.
31 Consequently, IL-1β and TNF-α may be associated with “nonspecific” chronic LBP when such degenerative changes are present at a subclinical level. It is also believed that IL-1, IL-6, and TNF-α induce and enhance the expression of matrix metalloproteinases, leading to regression of a herniated intervertebral disk.
31 Thus, this belief provides another possible explanation for the presence of inflammatory cytokines in patients with “nonspecific” chronic LBP. It also provides a rationale for the significant pairwise correlations that we observed between baseline concentrations of both IL-1β and IL-6 and the number of key osteopathic lesions.
A cross-sectional study
32 of 23 patients with chronic LBP attributed to herniated intervertebral disks and 10 healthy controls found significantly increased concentrations of IL-6 and TNF-α, but not of IL-1β, in patients with LBP. Another study
33 of 94 patients with chronic neuropathic, nociceptive, or mixed pain for greater than 6 months and 6 healthy controls found a dose-response relationship between increasing cytokine concentrations (including IL-1β, IL-6, and TNF-α) and increasing pain severity.
Tumor necrosis factor-α was evaluated in a longitudinal study of 120 patients with LBP and 120 matched healthy controls.
34 This study had several methodologic features that were similar to the features in our study, including patients with nonspecific chronic LBP, exposure to a treatment regimen, and several months of follow-up using a VAS for LBP and the RMDQ. At baseline, 58% of LBP patients were considered “positive” for TNF-α (serum TNF-α concentration >2 pg/mL) vs 12% of healthy controls. The percentage of TNF-α positives declined after 10 days of treatment and then remained stable for 6 months, whereas the percentage of TNF-α positives among controls remained stable throughout the entire study. Although VAS pain and RMDQ scores also declined over time, the change in TNF-α concentration was not predictive of clinical outcomes in the LBP patients. Our subgroup analyses found that the reduction in TNF-α concentration with OMT was indeed associated with improvements in LBP and back-specific functioning.
It has been known for more than 2 decades that peripheral immune challenges lead to the activation of discrete circuitries within the central nervous system via both hematogenous and neural pathways, thereby facilitating changes known as sickness responses.
35 Cytokines are sickness-inducing agents that facilitate pain by creating a well-defined immune-to-brain-to-spinal cord pathway, in which the ventrolateral medulla-to-spinal cord limb of the pathway leads to release of neurotransmitters or neuromodulators that activate spinal cord glia and enhance pain.
35 Such pain facilitation is preventable by blocking the actions of cytokines, including TNF-α.
36 Two TNF-α inhibitors, infliximab
37 and etanercept,
38 each yielded encouraging results in open-label studies involving disk-related sciatica. A recent randomized controlled trial
39 found significantly better pain outcomes in patients with sciatica 4 weeks after the epidural administration of etanercept, compared with those who received dexamethasone. However, a blinded, placebo-controlled trial found no significant clinical benefits 52 weeks after a single intravenous infusion of infliximab.
40 On the basis of our findings, it is reasonable to hypothesize that OMT may serve to effectively reduce serum TNF-α concentration and thereby alleviate pain in patients with nonspecific chronic LBP. More research on this hypothesis appears warranted, given the safety and potential cost advantages of OMT relative to commercially available TNF-α inhibitors.
Despite the strengths of nesting this study within a randomized controlled trial, there are potential limitations of our study. First, because the analyses involved 5 cytokines and 4 clinical measures, it is possible that some significant findings may represent type I errors because of these multiple comparisons. Nevertheless, because we desired to generate hypotheses for future testing within this exploratory study, we elected not to adjust for multiple comparisons. Second, and conversely, type II errors may have occurred because only 15% of OSTEOPATHIC Trial patients had pretreatment cytokine measures and 12% had matched posttreatment measures. Although there were several significant findings in this study, it is possible that other important associations may have been missed because of limited sample size. Third, cytokine concentrations may vary diurnally or because of other confounders, such as medication use, that were not tightly controlled in our study. Generally, we believe that the randomization process would have mitigated such potential confounders by allocating them comparably between the OMT and sham OMT groups. The matching of patient pre- and post-treatment cytokine measures further diminished the potential for confounding bias.