Darcy Vavrek ND MS, Mitch Haas DC MA, Dave Peterson DC
Center for Outcomes Studies,
Western States Chiropractic College,
2900 NE 132nd Ave.,
Portland, OR 97230, USA.
OBJECTIVE: Objective clinical measures for use as surrogate markers of cervicogenic headache (CGH) pain have not been established. In this analysis, we investigate relationships between objective physical examination (PE) measures with self-reported CGH outcomes.
METHODS: This is an exploratory analysis of data generated by attention control PE from an open-label randomized clinical trial. Of 80 subjects, 40 were randomized to 8 treatments (spinal manipulative therapy or light massage control) and 8 PE over 8 weeks. The remaining subjects received no PE. Physical examination included motion palpation of the cervical and upper thoracic regions, active cervical range of motion (ROM) and associated pain, and algometric pain threshold evaluated over articular pillars. Self-reported outcomes included CGH and neck pain and disability, number of CGH headaches, and related disability days. Associations between PE and self-reported outcomes were evaluated using generalized linear models, adjusting for sociodemographic differences and study group.
RESULTS: At baseline, number of CGH and disability days were strongly associated with cervical active ROM (P < .001 to .037). Neck pain and disability were strongly associated with ROM-elicited pain (P < .001 to .035) but not later in the study. After the final treatment, pain thresholds were strongly associated with week 12 neck pain and disability and CGH disability and disability days (P < or = .001 to .048).
CONCLUSIONS: Cervical ROM was most associated with the baseline headache experience. However, 4 weeks after treatment, algometric pain thresholds were most associated. No one PE measure remained associated with the self-reported headache outcomes over time.
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From the FULL TEXT Article:
We have noted that, at baseline, the study participants’ subjective headache experience was most associated with PE measures of inclinometric cervical active ROM and elicited pain. However, this pattern shifted at week 12, 4 weeks after the final treatment. At week 12, the measure most associated with study participants’ CGH subjective outcomes was the final examination pain pressure threshold.
Inclinometric cervical active ROM and elicited pain might be expected to be more associated with higher CGH and neck pain levels early on due to potential associated splinting or muscle injury. This association did not appear in all participants because 11 (~25%) of 40 participants reported no pain on cervical ROM at baseline. However, visual inspection of the raw data shows that those who had pain elicited by cervical active ROM also had worse subjective outcomes at baseline.
Later on, after the application of manual medicine, it is expected that the relationship of baseline inclinometric cervical active ROM and elicited pain with headache/neck pain would decrease. However, with the improvement of many study participants, zero pain reported on cervical ROM increased from 11 to 20 (~50%) out of the 40 participants at their final PE; it is difficult to establish any type of linear relationship with this type of floor effect.
Differences observed between groups at low dose may be more pronounced at a higher dose as they were with the subjective outcomes. Inasmuch as these PE outcomes are associated with the subjective patient-reported outcomes, we might see a stronger association between the 2 at a higher dose. Future studies that include cervical ROM and associated pain as secondary outcomes, measured by a blinded study physician, will allow clinicians to assess these higher dose relationships.
The fact that pain pressure threshold over paraspinal tissues and joints is associated with headache/neck pain disability and frequency at 12 weeks, but not consistently throughout, is puzzling. This can be explained, in part, by the fact that the pain pressure threshold increases as the patient improves, thus avoiding the floor effect limitation that occurs in the other PE measures. In addition, the development of a relationship at 12 weeks between pain pressure threshold and persistent headaches may have occurred because other musculoskeletal components potentially associated with the neck pain and headaches were not fully affected by thrust manipulation. Perhaps SMT improved joint mobility without fully ameliorating other soft tissue components of CGH such as paraspinal trigger points. Although we were underpowered to detect this type of result, both treatment groups experienced this change in association. Still, it is likely that those who continue to have a low pain pressure threshold tolerance are more likely to have persistent symptoms and thus be candidates for further manual care.
No one PE measure remained associated with the self-reported headache discomfort questions over time. This is likely due to patient improvement or a widespread floor effect. Thus, no single objective PE surrogate measure for CGH clinical research is suggested by this study as a useful longitudinal outcome.
A different analytical approach to the data would have been to do a prediction analysis of the data to assess if these baseline PE measures are predictive of treatment outcome, as has been done by Jull and Stanton,  who found no consistent predictors of reduction in CGH. This will be our next analysis.
It is interesting to note that study subjects in both groups remained restricted on cervical extension after treatment (20° or 55° out of 75°, restriction on average). Cleland et al  reported restricted cervical extension as predictive of success with SMT. Restricted cervical extension may be a part of the pathophysiology of the CGH. In addition, perhaps decreased cervical ROM on extension is indicative of a population who might experience chronic CGHs and could be a future focus of treatment assessment.
The treating physicians who performed the attention control PE were not blinded to treatment arm after baseline. As a result, there might be significant bias in physician expectation of improvement based both on time in the study and upon treatment group assignment. However, the lack of differences between groups mitigates this concern to some degree.
With this sample size, 20 patients per treatment arm, there was minimal power to detect an association between PE and subjective outcome measures or the effect of treatment on the observed associations. The results obtained here need to be repeated by larger studies with blinded assessors to further flush out the pathophysiology of CGH.
There might be an observable relationship between patient-reported CGH measures and PE measures with a higher treatment frequency. It is possible that this potential relationship might be different between the SMT and LM groups. We plan to look at this in future studies.
The PE measures, excluding pain pressure threshold and cervical extension, all had a floor effect. As study subjects improved, the values hovered closer and closer to 0 (or normal), allowing for small amounts of variance. Although the study design excluded subjects whose CGH pain scored lower than 25 to mitigate a floor effect, baseline PE pain scores still had a maximum average of 2.3 on a 0-to-10 pain scale. Even the cervical active ROM scores were within 8° of normal ROM, on average, at baseline. Surrogate measures are difficult to find under these constraints.
Subjects answered questions about their experience over the past 4 weeks after the fact introducing a potential recall bias. Optional headache diaries were provided but not collected throughout the study to prevent this risk of bias. We chose not to require this to decrease study patient burden, thus relying on collecting the patient’s subjective experience every 4 weeks throughout the study.
Generalizability beyond randomized clinical trial protocol is not clear. Subjects enrolled in the study went through a telephone screen and 2 baseline examinations and had to meet study criteria before enrollment. Larger clinical trials on headache populations that gather longitudinal PE data will help to establish the generalizability of these results.
At 12 weeks, a lower pain pressure threshold was indicative of those that still had the most intense subjective experience with headache pain vs cervical active ROM and pain with movement. This relationship is different from that at baseline, where the reverse was true. It is also important to note that cervical extension remained restricted throughout the study, indicating a possible direction for the study of pathophysiology behind CGHs. Although this is useful information for the practicing clinician who may use these PE indicators to track patient progress, no consistent surrogate PE measure for the CGH experience is indicated.
Yet, clinically important changes over time were observed in PE indicators for self-reported CGH pain and disability outcomes. This is an important step toward establishing objective measures of CGH pain and disability for clinical studies.
Funding Sources and Potential Conflicts of Interest
No conflicts of interest were reported for this study. This study was supported by the National Center for Complementary and Alternative Medicine, Department of Health and Human Services (grant no. R21 AT002324).