J Manipulative Physiol Ther 2005 (Jun); 28 (5): 294–302 ~ FULL TEXT
Charlotte Leboeuf-Yde, DC, MPH, PhD, Eva N. Pedersen, MS, Peter Bryner, MChiroSc,
David Cosman, DC, Ray Hayek, MChiroSc, PhD, William C. Meeker, DC, MPH,
Junaid Shaik J, MTechChirog, Octavio Terrazas, DC, John Tucker, ME, PhD,
Max Walsh, MSc, MAppSc
Back Research Center,
Backcenter Funen, Denmark.
OBJECTIVE: To replicate a previous study of nonmusculoskeletal responses to chiropractic intervention and to establish whether such responses are influenced by the country of study, chiropractors' attitudes, and information to patients, patients' demographic profiles, and treatment regimens.
METHODS: Information obtained through questionnaires by chiropractors and patients on return visit within 2 weeks of previous treatment from chiropractic practices in Canada, United States, Mexico, Hong-Kong, Japan, Australia, and South Africa. In all, 385 chiropractors collected valid data on 5607 patients. Spinal manipulation with or without additional therapy was the intervention provided by chiropractors. Outcome measures included self-reported improved nonmusculoskeletal reactions (allergy, asthma, breathing, circulation, digestion, hearing, heart function, ringing in the ears, sinus problems, urination, and others).
RESULTS : The results from the previous study were largely reproduced. Positive reactions were reported by 2% to 10% of all patients and by 3% to 27% of those who reported to have such problems. Most common were improved breathing (27%), digestion (26%), and circulation (21%). Some variables were identified that somewhat influenced the outcome: patients informed that such reactions may occur (odds ratio [OR] 1.5), treatment to the upper cervical spine (OR 1.4), treatment to lower thoracic spine (OR 1.3), and female sex (OR 1.3). However, these had a very small "explanatory" value (pseudo R2 3%).
CONCLUSION: A minority of patients with self-reported nonmusculoskeletal symptoms report definite improvement after chiropractic care, and very few report definite worsening. Future studies should use stringent criteria to investigate a possible treatment effect and concentrate on specific diagnostic subgroups such as digestive problems and tinnitus.
From the FULL TEXT Article:
The possible link between spinal adjustments and changes in nonmusculoskeletal conditions has intrigued the chiropractic profession since the days of its founder, D.D. Palmer.  Some have argued that spinal adjustments sometimes improve visceral conditions, whereas others claim that they only remove symptoms that mimic internal organ disease. 
In a recent practice-based multicenter study, a pattern
was identified of unexpected positive nonmusculoskeletal
responses (N-MSRs) reported by patients after chiropractic
care.  However, in that study, because there was no untreated control group, it was not possible to determine whether these responses were caused by the treatment, if they constituted mere signs of natural variation in the human physiology, or if they were figments of imagination.
To determine whether there is a causal link between the
treatment and the symptom improvement, it would be
necessary to conduct a number of randomized controlled
trials. Such studies should include specific and valid
outcome measures in relation to each N-MSR under
scrutiny. This would be time consuming and expensive
and not within the capability of most researchers at this time.
Therefore, to provide stronger data on the potential
relationship between treatment and symptom improvement,
a similar but expanded approach was taken to determine if
the findings in the first study could be replicated in a much
larger international sample. Additional objectives of the
study were to establish whether N-MSRs were influenced
by (a) the chiropractors’ attitudes to N-MSR and the
information they gave to their patients on this subject, (b)
patients’ demographic profiles (age, sex, education, and
work status), and (c) treatment profiles (type of treatment
provided, area treated, number of areas treated, and number
of treatments over time).
The reaction pattern in our international study was found
to be similar across countries, and this pattern, in turn, was
similar to the one identified in the previous Swedish study.
These observations indicate either (1) that this is indeed a
typical pattern of treatment effect that can be observed in
chiropractic practice, (2) that this is how nonmuscular
symptoms fluctuate as a function of being under care but not
as a direct effect of care, (3) that this is how they fluctuate
because they are under observation, or (4) that this
is simply how nonmuscular symptoms fluctuate in the
Furthermore, a number of variables were identified that
may have an effect on the reporting of N-MSRs, although
these bexplainedQ an exceedingly small part of the variation
(only 3%). These variables were, for example, sex and the
spinal area treated. The ORs for reporting improved
digestion, allergy, hearing, or urination ranged between
1.4 and 4.1 (Table 4) in patients treated (at least) in occiput
to C3 versus those treated in any other area(s). It was also
more likely that patients treated in the upper half of the
thoracic spine reported improved symptoms in breathing
and circulation (both ORs 1.7).
Whether the latter reports actually describe N-MSRs as opposed to purely somatic symptoms is, however, uncertain. Problems with breathing, such as pain on inspiration, could be purely mechanical,  and symptoms of diminished circulation are seen to occur with radicular problems of the upper limbs, commonly treated in the thoracocervical regions.  Because most patients were treated in several spinal areas, it was impossible to investigate the outcome pattern for specific
spinal areas in relation to specific conditions, such as
the upper thoracic spine and hearing, as described by
D.D. Palmer. 
Patients who attended a larger number of visits over the
past month were also more likely to report at least 1 NMSR.
There are 3 possible reasons for this: (1) several visits
are likely to provide the chiropractor with more opportunities
to influence the patient mentally, (2) several treatments may be needed to produce a physiological effect, and (3) a larger number of visits occur over a longer duration, giving a greater chance for nonmusculoskeletalsymptoms to fluctuate spontaneously, as previously suggested. 
Interestingly, in the multivariable analysis, the effect of
the number of visits — variable on the reporting of NMSRs —
was not dependent on the 2 chiropractor-specific variables (subluxation is important and information to patients that N-MSRs are likely to occur). This indicates that the response observed in relation to the number of visits was not directly related to the amount of information received. Further data interpretation fails to strengthen the second possibility because the number of spinal areas treated is unrelated to the reporting of N-MSRs (contrary to the Swedish study). No conclusions can therefore be drawn on this issue.
Other variables examined in this study did not have an
effect on the reported outcome. These variables were level
of education, type of work, and type of treatment. The latter
finding is interesting in that it shows that classical spinal
adjustments are no more likely to be associated with NMSRs
than, for example, mobilization. The fact that there is
no difference between treatment methods tends to weaken
the btreatment effectQ explanation and strengthens the
alternative explanations as described above.
If we assume that all patients, identified in the study to
have a nonmusculoskeletal problem, were able to accurately
identify specific N-MSRs and if we also assume that those
who reported a change in status did so as a result of the
treatment, approximately one quarter of patients with
breathing or digestive problems became definitely better,
whereas only 1% became definitely worse. Approximately
one fifth of those with circulation problems, ringing in the
ears, or asthma reported definite improvement, and 2% or
less became definitely worse. The proportions of definitely
improved patients were approximately 10% or less for
the other conditions studied in this study, with bdefiniteQ
negative side effects never exceeding 2% (Table 2). If these
assumptions are correct, it appears that chiropractic care for
this type of conditions is only weakly to moderately
successful but, at least, rarely harmful.
When interpreting the results of this study, it is important
to keep in mind its weaknesses, including the potential for
sampling bias (both of chiropractors and of patients), uncertainty surrounding patients’ recall ability, problems
with accurate description of variables in the questionnaire,
and patients’ understanding of these, expectation bias that
may have arisen before meeting the present chiropractor,
and the possibility that N-MSRs may be missed if they
require more than 2 weeks to manifest themselves or if
patients are unable to identify these themselves. Another
obvious limitation is the absence of a control group to
compare the results against, which would be necessary to
investigate treatment effects. It is therefore not possible
to establish whether patients improved (or worsened)
because of the treatment, despite the treatment or regardless
of the treatment.
On the other hand, practice-based research is more likely
to reflect everyday clinical practice than the procedures used
and results obtained in bgold standardQ–controlled clinical
trials, in which highly selected clinicians and patients
participate. Furthermore, the methodology adopted in this
study makes it possible to obtain a large sample size at a
relatively low cost, which allows for meaningful subanalyses
through the use of internal control groups. This made it
possible for us to test the influence of various factors that
could be suspected to influence treatment outcome. These
include information to patients regarding nonmusculoskeletal
benefits of chiropractic care and the type and area
An important quality issue in this type of study, with
volunteer participants, is that of the study’s external validity. Our study participants consisted of a large proportion of chiropractors who believed firmly in the subluxation and in
N-MSRs. It is not known if they are representative of the
general chiropractic population. In fact, it is possible that
chiropractors who elected to participate in this study were
proponents of the concept under scrutiny. In a previous
study of selected clinicians, the percentage of patients
consulting their chiropractor for a nonmusculoskeletal
complaint (10%) was approximately the same as in the
present study (8%).8 A previous Australian practice-based
study noted a change in digestive symptoms similar to our
results.  Furthermore, the fact that the outcome pattern in our study was so similar to that of the previous Swedish study, which was carried out among chiropractors generally without strong convictions concerning nonmusculoskeletal effects, is yet another argument in favor of the possibility that the patient profile in relation to N-MSRs is largely unaffected by the chiropractors’ beliefs and attitudes.
An additional method to investigate the external validity
in studies in which particular characteristics of some
clinicians can result in a nonrandom aggregation of patients
with particular features is to control statistically for the
clustering effect. In our study, such clustering effect could
arise as a result of the research officers’ choice of
participating chiropractors and also because of the individual
chiropractors’ selection of patients. According to our
results, the variable btreating chiropractorQ did not remove
any of the previously noted associations with the outcome
variable, but the variable research officer did have the
effect of removing the link between subluxation and the
outcome variable. This means that at least some research
officers invited chiropractic participants who were similar in
their beliefs on the subluxation issue.
The findings in the present study were largely similar to
those of the previous Swedish study. A minority of patients
with self-reported nonmusculoskeletal symptoms report
definite improvement after chiropractic care, and very few
report definite worsening. Some factors relating to the
chiropractor, the treatment, and the patient were found to be
weakly associated with the outcome but these factors
explained only a small fraction, approximately 3%, of
It is recommended that further research in this area would
concentrate on specific disorders that are most likely to
produce positive results, such as specifically identified
subgroups of digestive problems or tinnitus, and that such
research, whether purely experimental or clinical, use
stringent research criteria such as random allocation, objective
measurements, sham treatment, and observer blindness.
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