The Innate Central Nervous System Immune Response to an Experimental Immune Challenge in People With Fibromyalgia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Innate Central Nervous System Immune Response to an Experimental Immune Challenge in People With Fibromyalgia (NCT04263454), a non-randomized phase 2, phase 3 study. The primary outcome is Change in Ratio of Choline/ Creatine (CHO/CR) in the Brain From Baseline to 3 Hrs Post-endotoxin Administration.

2. Clinical Question

The study asks whether the innate immune response in the brain differs between people with fibromyalgia and healthy controls after an experimental immune stimulus. Magnetic resonance spectroscopy (MRS), performed using MRI, was used to assess a change in the brain’s choline-to-creatine ratio from baseline to three hours after endotoxin administration. The registry describes choline as a marker of increased cell turnover that can be seen during neuroinflammation.

The research question is about a measured response to a challenge, not a comparison of treatments intended to relieve symptoms. The groups were not randomly allocated, and the registry specifically cautions that they are not a like-for-like control comparison. Therefore, a difference between groups, if reported, would need to be interpreted in light of how participants entered each group and any other differences between them.

Numerical results for this primary question are not reported in the registry record. The posted information therefore describes the intended comparison and measurement, but does not establish the size, direction, or precision of a group difference.

3. Trial Design

This completed study is listed as phase 2 and phase 3, with a parallel-group, nonrandomized allocation and triple masking. The registry lists 36 enrolled participants. Because allocation was nonrandomized, the group comparison should not be read as if participants had been randomly assigned to otherwise interchangeable groups. The registry explicitly flags that the arms are not a like-for-like control comparison.

The groups were Healthy Control and Fibromyalgia. The fibromyalgia group was required to meet the 2010 American College of Rheumatology diagnostic criteria. Healthy controls were required to report no other medical conditions, including fibromyalgia. Both groups were described as undergoing the same screening and experimental procedures. The study intervention listings include Escherichia coli endotoxin and magnetic resonance spectroscopy.

The study’s central procedure was an experimental immune challenge followed by brain imaging. The primary endpoint specifies a measurement from baseline to three hours after endotoxin administration. The healthy-control arm description gives an MRI before and three hours after 0.4ng/kg; further dosing details are not reported in the registry record. The listed start date is 2020-03-11, and the primary completion date is 2021-12-22. The registry status is completed.

The registry lists 3 outcome measures and 0 analyses. Numerical primary outcome findings, analysis details, and further information about how the enrolled participants were distributed across the outcome population are not reported in the registry record. The phase labels and masking description identify features of the registered design, but do not supply details of the statistical analysis plan, masking procedures, or sample-size justification.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: as defined in participant flow

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: analysis population as defined in participant flow

6. Primary Endpoint

The registry lists the primary outcome as Change in Ratio of Choline/ Creatine (CHO/CR) in the Brain From Baseline to 3 Hrs Post-endotoxin Administration, measured over 3 hours (From Baseline to 3 Hrs Post-endotoxin Administration).

The primary endpoint is the mean change in the brain choline-to-creatine (CHO/CR) ratio from baseline to three hours after endotoxin administration. It is a continuous measurement, reported in ratio units, with standard deviation specified as the measure of dispersion. MRI-based magnetic resonance spectroscopy is used to assess the brain metabolite measurement.

The registry describes choline (CHO) as a marker of increased cell turnover that can be seen during neuroinflammation. The study uses the brain metabolite measurement to examine whether the response following an experimental immune stimulus differs between people with fibromyalgia and healthy controls. A ratio can express one metabolite measurement relative to another, but the registry’s stated rationale focuses on CHO as the neuroinflammation-related marker.

This endpoint is a biological measurement at a specified time after a challenge. It is not itself a direct measure of symptoms, daily functioning, or a clinical benefit. Nor does a change in this ratio, on its own, establish that inflammation caused a symptom or condition. It is best understood as a research measure of brain metabolic response.

The registry record does not report the group means, standard deviations, estimated difference, or uncertainty for this endpoint. Consequently, the magnitude and precision of the primary comparison cannot be assessed from the information reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The methods listed in the registry describe the endpoint as a mean of a continuous measurement. The main quantity is change in the CHO/CR ratio from baseline to three hours after endotoxin administration. A change score expresses how a measurement differs between two time points for the measured participant. Comparing average changes between groups addresses whether the groups had different average measured responses over that interval. The registry record does not provide the group-level values or the estimated contrast.

What does a mean describe?

In general, a mean is the arithmetic average of measurements in a group. It provides a summary of the group’s central level, but it does not show every participant’s value or the shape of the distribution. Two groups can have similar means while their individual measurements vary substantially, or their means can differ while their distributions overlap. These are general features of summaries; the registry record does not report the distributions for this outcome.

The registry names standard deviation as the dispersion measure. In general, a standard deviation describes how spread out individual measurements are around their group mean. It is not the same as the uncertainty in the estimated mean or in a difference between means. Uncertainty in a comparison depends on factors including the amount of information available and the variability in the measurements. The registry record does not give the outcome standard deviations or a confidence interval for the group comparison.

How should an estimated difference be read?

For a continuous endpoint, a group contrast can express how far apart the average changes are, with a direction determined by the subtraction order. The numerical estimate would describe the observed contrast in the endpoint’s units. Its uncertainty interval would show which values remain compatible with the data under the method used to calculate that interval. A narrow interval indicates greater precision than a wide interval, while an interval that includes no difference would mean the data are compatible with no group contrast as well as with some contrasts in either direction. These are general explanations; the registry record does not report an estimated contrast, interval, or p-value for the primary outcome.

A p-value, when reported, is a measure of how incompatible the observed data are with a specified statistical model or null hypothesis. It is not the probability that the null hypothesis is true, and it does not describe the size or clinical importance of a difference. No primary p-value is reported in the registry record. Without an effect estimate and its precision, a significance label alone would not be enough to describe the evidence, even if one were available.

Why does the nonrandomized design matter?

The registry identifies the study as nonrandomized and cautions that its arms are not a like-for-like control comparison. In general, random allocation helps balance measured and unmeasured participant characteristics on average, whereas a nonrandomized comparison may retain differences between groups. Such differences can complicate interpretation of an observed contrast because the contrast may reflect both group membership and other factors associated with the groups. This is a general design consideration, not evidence that a particular imbalance occurred in this study. Baseline comparisons, covariate adjustment, and the rationale for any adjustment are not reported in the registry record.

Triple masking is listed as a design feature. Masking can, in general, reduce the influence of knowledge about group assignment on aspects of study conduct or assessment. The registry record does not describe which parties were masked, how masking was implemented, or whether it was maintained. Masking does not remove the potential for baseline differences in a nonrandomized comparison.

What does the planning framework mean?

The registry describes its sample-size illustrations as planning calculations based on the observed effect, rather than the trial’s own design. The stated calculation assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the target effect is a stated fraction of the observed effect. For non-time-to-event outcomes, the illustrations are expressed as participants per arm for 80% or 90% power, while time-to-event calculations use a total number of events. These are planning illustrations, not observed power and not the number of participants analyzed in this trial. The actual illustration values are not reported in the registry record.

In general, a sample-size calculation estimates how much information a future study would need under specified assumptions about the effect and variability. Its result depends on those assumptions and should not be mistaken for a finding from the completed study. A calculation based on an observed effect is especially dependent on that estimate, and the registry does not report the outcome estimate needed to evaluate it. A trial’s enrollment figure is also not interchangeable with the number included in a particular analysis.

Over-dispersion is a general concern for some statistical models when observed variation exceeds what the model assumes. It can make standard errors and resulting uncertainty estimates unreliable if the model fails to account for the extra variation. The registry identifies this endpoint as continuous and does not describe a count model or report a model-based analysis. Whether over-dispersion was relevant to any analysis is not reported in the registry record.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Healthy Control", "Fibromyalgia")
n   <- c(13, 12)
m   <- c(-0.0021, -0.0058)
sp  <- c(0.01664, 0.01465)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Healthy Control  13  -0.002  0.017  -0.012  0.008
CARM  Fibromyalgia  12  -0.006  0.015  -0.015  0.004

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 3 outcome measures, but the primary endpoint is the change in the CHO/CR ratio from baseline to three hours after endotoxin administration. The registry lists 0 analyses. A statistical plan describing how the primary outcome was analyzed, or how multiple outcomes were handled, is not reported in the registry record. In particular, whether any multiplicity adjustment was planned or applied is not reported in the registry record.

In general, testing several outcomes or several contrasts can increase the chance of at least one apparently unusual result arising by chance. A prespecified primary outcome and a clearly described multiplicity strategy help readers distinguish the main inferential question from additional analyses. The registry’s outcome count alone does not reveal how many formal hypotheses were tested, which comparisons were planned, or whether results were adjusted.

The outcome population is described as defined in participant flow. The detailed analysis population, participant flow for the endpoint, and the number of measurements included in each group’s primary analysis are not reported in the registry record. The registry also does not report how missing outcome measurements were handled, whether missingness was assessed, or whether any sensitivity analyses were conducted.

In general, missing-data methods matter because an analysis of available measurements can be affected if the absence of a measurement is related to the value that would have been observed. Imputation and sensitivity analyses can address different assumptions, but their suitability depends on the study and the missingness process. No particular missing-data approach should be inferred for this study from the registry information.

Without the analysis population, missing-data approach, and multiplicity plan, readers cannot fully assess how the reported analysis set and inferential conclusions would relate to the original outcome question. The registry record does not report those details.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry reports serious adverse event counts separately for the Healthy Control and Fibromyalgia groups. For serious events, 0 of 13 participants at risk were reported as affected in Healthy Control, and 0 of 12 participants at risk were reported as affected in Fibromyalgia. The registry lists zero deaths in each group. It lists no top serious-event terms.

For other adverse events, 0 of 13 participants at risk were reported as affected in Healthy Control, and 0 of 12 participants at risk were reported as affected in Fibromyalgia. These figures are counts of participants reported as affected, not counts of every possible event, and they should not be combined across categories to create a new total.

In general, a zero count means that no affected participants were recorded for that category in the registry entry. It does not prove that the risk is zero, establish that all events were captured, or indicate how safety events were monitored. The registry record does not report additional detail about event definitions, collection procedures, follow-up duration for safety, or the severity of other adverse events. The nonrandomized group structure also means these counts should not be treated as a controlled comparison of safety between otherwise interchangeable groups.

13. What the Result Does, and Does Not, Mean

The study is designed to examine a biological response to an experimental immune challenge, using a brain metabolite ratio measured by MRI-based MRS. Its question concerns whether average changes differ between people with fibromyalgia and healthy controls. This is a mechanistic research question, rather than a direct test of symptom relief or a comparison of clinical treatments.

The registry describes increased CHO as a marker of increased cell turnover that can be seen during neuroinflammation. That description gives a rationale for measuring the metabolite, but the ratio is still a research measurement. A change in the ratio cannot, on its own, establish the presence, cause, or clinical consequences of brain inflammation. Nor does this endpoint directly measure pain, fatigue, daily function, or the course of fibromyalgia.

The registry record does not report numerical results for the primary outcome. It therefore does not show whether the mean change was greater in one group, how large any difference was, or how precise an estimate might be. The completed status and enrollment figure do not answer those questions. The record also does not report the statistical analysis details needed to evaluate an adjusted or unadjusted comparison.

The nonrandomized design further limits causal interpretation. In general, differences between groups can reflect characteristics associated with group membership as well as response to the experimental stimulus. The registry itself cautions that the arms are not a like-for-like control comparison. This does not show that a particular source of bias affected the findings; it means that the design does not warrant treating any group contrast as a randomized causal effect.

The reported safety counts describe the registry’s recorded serious and other adverse-event categories for the listed at-risk participants. They do not establish that the procedure is risk-free. Overall, the record documents the research question and study framework, but numerical primary findings and their uncertainty are not reported in the registry record. No conclusion about the magnitude or direction of the measured response can be drawn from the available result information.

14. Why This Trial Matters Statistically

This study is statistically interesting because it pairs an experimental immune challenge with a repeated brain measurement. Measuring the CHO/CR ratio at baseline and after the challenge focuses the question on change over time, rather than only on a single measurement. The comparison then asks whether that average change differs between the fibromyalgia and healthy-control groups.

The design also highlights why a clear account of allocation matters. The registry identifies the study as nonrandomized and explicitly warns that the groups are not a like-for-like control comparison. That information shapes how an estimated group contrast should be interpreted: even a precise contrast would not, by itself, show that group status caused the difference. Statistical precision and causal strength are distinct considerations.

The endpoint illustrates the distinction between a biological marker and a clinical outcome. A marker can help investigate a proposed mechanism, while its interpretation depends on what it measures and how strongly it represents the biological process of interest. Here, the registry describes CHO as a marker that can be seen during neuroinflammation, but the listed primary measure is a ratio and the record does not report outcome results. The endpoint therefore defines a testable research question without establishing its answer.

Finally, the record underscores the importance of reporting effect estimates, variability, uncertainty, analysis populations, and missing-data methods. Those details allow readers to judge both the magnitude and reliability of a finding. The registry reports the study’s completion and safety counts, but primary numerical findings and analysis methods are not reported in the registry record. Without them, the scientific question can be described, but the strength of the evidence cannot be evaluated quantitatively.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The most consequential limitation for interpreting the registered findings is that numerical results for the primary endpoint are not reported in the registry record. Without group summaries, an estimated contrast, and a measure of uncertainty, readers cannot assess the direction, size, or precision of the primary comparison. The registry lists 0 analyses, and further analysis details are not reported.

The nonrandomized allocation is an additional design limitation for group comparisons. The registry specifically cautions that the arms are not a like-for-like control comparison. In general, differences between groups may complicate attribution of an observed contrast to the experimental immune response. The registry does not report baseline balance or whether potential confounding was addressed.

Information about the endpoint analysis population and the handling of missing measurements is not reported in the registry record. The outcome population is described as defined in participant flow, but the details needed to assess who contributed data to the primary analysis are not reported. The multiplicity plan and any adjustment across outcome measures are also not reported.

The primary endpoint is a metabolite ratio measured at a specified time after an experimental challenge. It is a biological research measure, not a direct clinical outcome. The registry’s rationale describes CHO as a marker that can be seen during neuroinflammation; this does not make the measure a definitive or direct assessment of inflammation. Numerical findings would be needed to evaluate the observed signal, and additional context would be needed to interpret its biological significance.

Finally, the safety record reports zero affected participants in the listed serious and other adverse-event categories, but further event-collection and follow-up details are not reported in the registry record. These limitations constrain interpretation of the registered information; they do not establish what the unreported outcome values or methods would show.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: The Innate Central Nervous System Immune Response to an Experimental Immune Challenge in People With Fibromyalgia — NCT04263454.
• Registry record last updated 2023-04-14; status last verified 2023-03.
• Results first posted 2023-04-14.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

The registry describes a completed, nonrandomized, parallel-group study listed as phase 2 and phase 3, with triple masking. It enrolled 36 participants and compared a Fibromyalgia group with a Healthy Control group. The study examined response to an experimental Escherichia coli endotoxin challenge using MRI-based magnetic resonance spectroscopy.

The primary endpoint was mean change in the brain CHO/CR ratio from baseline to three hours after endotoxin administration, with standard deviation specified as the dispersion measure. The registry lists 3 outcome measures and 0 analyses. Numerical primary outcome results, the analysis population details, and the statistical methods are not reported in the registry record.

The registry reports zero participants affected by serious adverse events and zero deaths in each listed group; it also reports zero participants affected by other adverse events in each group. The study’s nonrandomized design and the registry’s warning that the groups are not a like-for-like control comparison are important when interpreting any group contrast.