Evidence of White Matter Neuroinflammation in [ME/CFS]: A Diffusion-Based Neuroinflammation Imaging Study 2026 Yu et al

[Andy]

ABSTRACT​

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating disorder with suspected neuroinflammatory pathophysiology. However, previous diffusion tensor imaging (DTI) studies have reported inconsistent white matter abnormalities in ME/CFS, and specific white matter inflammatory changes remain poorly characterised.

This study employed an advanced diffusion-based neuroinflammation imaging (NII) model to investigate white matter neuroinflammation in ME/CFS. Diffusion MRI data from 67 ME/CFS patients (median age, 38; and 54 women) and 67 rigorously matched healthy controls (HCs) (median age 38; and 52 women) were analysed. Seven NII-derived metrics were computed: hindered water ratio (NII-HR), restricted fraction (NII-RF), fibre fraction (NII-FF), axial diffusivity (NII-AD), radial diffusivity (NII-RD), mean diffusivity (NII-MD) and fractional anisotropy (NII-FA). Conventional DTI metrics were also calculated. Tract-based spatial statistics were used to perform voxel-wise group comparisons, and multiple regression analysis was conducted to examine the relationship between NII/DTI metrics and clinical measures of mental health, physical health, sleep quality, disability, disease severity and disease duration.

Compared to HCs, ME/CFS patients exhibited widespread white matter abnormalities, including significantly lower NII-HR and NII-RF, and significantly higher NII-FF, NII-AD, NII-MD and NII-FA across association, commissural and projection fibres. Additionally, some regions showed decreased NII-AD and NII-MD in ME/CFS. Lower NII-RF, NII-AD and NII-MD in ME/CFS were significantly associated with worse mental health, while lower NII-RF was also associated with a higher level of disability. Among ME/CFS patients, higher NII-FF was associated with lower disease severity. Conventional DTI showed minimal group differences and no significant clinical associations.

This study provides in vivo evidence of white matter neuroinflammation in ME/CFS, characterised by cerebral edema (reduced NII-HR), cellular infiltration (reduced NII-RF) and axonal reorganisation (increased NII-FF). This suggests NII-derived indices may serve as sensitive biomarkers for neuroinflammation in ME/CFS.

Open access

 

[V.R.T.]

ABSTRACT​

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating disorder with suspected neuroinflammatory pathophysiology. However, previous diffusion tensor imaging (DTI) studies have reported inconsistent white matter abnormalities in ME/CFS, and specific white matter inflammatory changes remain poorly characterised.

This study employed an advanced diffusion-based neuroinflammation imaging (NII) model to investigate white matter neuroinflammation in ME/CFS. Diffusion MRI data from 67 ME/CFS patients (median age, 38; and 54 women) and 67 rigorously matched healthy controls (HCs) (median age 38; and 52 women) were analysed. Seven NII-derived metrics were computed: hindered water ratio (NII-HR), restricted fraction (NII-RF), fibre fraction (NII-FF), axial diffusivity (NII-AD), radial diffusivity (NII-RD), mean diffusivity (NII-MD) and fractional anisotropy (NII-FA). Conventional DTI metrics were also calculated. Tract-based spatial statistics were used to perform voxel-wise group comparisons, and multiple regression analysis was conducted to examine the relationship between NII/DTI metrics and clinical measures of mental health, physical health, sleep quality, disability, disease severity and disease duration.

Compared to HCs, ME/CFS patients exhibited widespread white matter abnormalities, including significantly lower NII-HR and NII-RF, and significantly higher NII-FF, NII-AD, NII-MD and NII-FA across association, commissural and projection fibres. Additionally, some regions showed decreased NII-AD and NII-MD in ME/CFS. Lower NII-RF, NII-AD and NII-MD in ME/CFS were significantly associated with worse mental health, while lower NII-RF was also associated with a higher level of disability. Among ME/CFS patients, higher NII-FF was associated with lower disease severity. Conventional DTI showed minimal group differences and no significant clinical associations.

This study provides in vivo evidence of white matter neuroinflammation in ME/CFS, characterised by cerebral edema (reduced NII-HR), cellular infiltration (reduced NII-RF) and axonal reorganisation (increased NII-FF). This suggests NII-derived indices may serve as sensitive biomarkers for neuroinflammation in ME/CFS.

Open access

This sounds like it could be absolutely massive, so I assume someone is going to be along to point out how deeply flawed it is any minute

 

[V.R.T.]

ME/CFS patients were interviewed by two clinicians to confirm a Canadian Consensus Criteria (CCC)-consistent (Carruthers et al. 2003) diagnosis of ME/CFS. A consensus diagnosis approach was employed to minimise the risk of an ill-defined disease cohort. The study intentionally recruited HCs with sedentary lifestyles (< 60 min in moderate or high-intensity activity [i.e., exercise] per week) to reduce the confounding effects of disease deconditioning (Nijs et al. 2011).

 

[Liie]

sedentary lifestyles (< 60 min in moderate or high-intensity activity [i.e., exercise] per week)

Up to 60 min moderate activity doesn't sound very intensely sedentary to me. But the study is probably better with this condition than without, anyway.

 

[butter.]

One of those studies that will need replication by multiple teams. It would be great to see that sooner rather than later. As far as I understand, this technique is also not fully established/standardized yet. I was involved in funding a more “standard DTI” MRI study in the past, but I am obviously not an expert. Certainly curious to learn more about this.

It's not a technique that requires a special MRI machine I think, it's more a software/normative datasetd issue, I believe?

 

[Jonathan Edwards]

I had a quick read through and found it very hard to see any data in an intelligible form. That may just be the way recent fashions in presentation go against the way I am used to reading papers but I am not so sure.

 

[Liie]

How does this relate to the work of other researchers who talk about "neuroinflammation" and "microglia activation" and similar things?

 

[V.R.T.]

I'd be interested to know what @SNT Gatchaman thinks of this paper

 

[Jonathan Edwards]

How does this relate to the work of other researchers who talk about "neuroinflammation" and "microglia activation" and similar things?

Inasmuch as I can follow the paper they are suggesting a change in water content in white matter, which is a characteristic feature of most inflammation. If it is real it would be a good indicator of very low level inflammation (anything more in terms of water change in brain tends to lead to coma).

They are also suggesting a change in cellularity although I doubt they can pin that down to microglia, which would be the inflammatory cell. They cite NAkatomi but the signal in Nakatomi's study was not in white matter particularly. It was mostly down in midbrain and brainstem I think. And it was not replicated.

It might be that this is finally going to give us evidence of structural change in brain of a low-grade inflammatory type. However, (1) they point out the inconsistency of previous studies and this one may be no different and (2) it may be better to analyse this in terms of the raw data - water, cell and fibre changes, without premature labelling as inflammatory.

 

[Casterofspells]

How does this relate to the work of other researchers who talk about "neuroinflammation" and "microglia activation" and similar things?

It certainly is a shame that Dr. Younger is teaching at the moment because of the NIH funding situation. It’ll be exciting to see what his PET and MRI imaging combo reveals.



He seemed pretty confident he had something in his last update. Has to be substantiated of course.

 

[SNT Gatchaman]

Follow-on from Distinct white matter alteration patterns in post-infectious and gradual onset chronic fatigue syndrome revealed by diffusion MRI (2025)

Looks like a high quality study, with care to correctness of inclusion criteria and matching. Advanced diffusion imaging techniques run on high-end scanners: Siemens Skyra 3T magnet, with a 64 channel head coil.

it may be better to analyse this in terms of the raw data - water, cell and fibre changes, without premature labelling as inflammatory.

Yes we should keep in mind this may not be inflammation in the classic sense as Jo has always cautioned. I think this new technique might have been mostly validated in MS and mouse models of MS where inflammation is known. The paper does ask for multi-modality supportive evidence (noting direct tissue assessment is always a challenge in the CNS).

although the NII model offers biologically informed metrics, it is still an indirect measure of neuroinflammation and does not differentiate between specific inflammatory cell types or processes. Validation with other neuroinflammation-specific techniques would strengthen the interpretations.

The observed higher NI in ME/CFS patients further supports the presence of neuroinflammatory processes, where the increased NII-FF may reflect neuroinflammatory-driven axonal swelling, gliosis, or reorganisation of axonal fibres. These increases could also reflect compaction or decreased tortuosity of axonal bundles, a response that has been observed in inflammatory or metabolic stress states where extracellular space shrinks and glial processes encroach on axonal domains.

I'd still also like to see myelin water fraction analysis applied to ME/LC to see if myelin compaction or rarefaction might explain some clinical and imaging findings.

Up to 60 min moderate activity doesn't sound very intensely sedentary to me.

But well matched.

The MET rate of the task from the Actigraph data was calculated to measure the activity level for each participant.

ensured that there were no significant group differences in age, sex, body mass index (BMI), metabolic equivalents (MET) rate or MRI scan time

As far as I understand, this technique is also not fully established/standardized yet.

New to me but I'll try and summarise the ideas and break things down. Though bear in mind it's decades since I looked at MRI physics and things have moved on a lot. I only keep the broadest of overviews of what I need when reading studies, rather than acquiring data or setting up research protocols, so I don't have the knowledge to judge more than they describe for us.

I'll have to come back to it this evening.

 

[Hutan]

The senior author is Zack Shan. He has a very good reputation and a bit of a track record in ME/CFS.

Group comparisons in each NII/DTI-derived metrics were performed using general linear models controlling for sex, age, BMI, MET, depression and anxiety scores via FSL's randomise tool (Winkler et al. 2014) with 10,000 permutations at each voxel, and multiple regression analyses were also performed using the randomise tool to examine the associations between NII/DTI-derived metrics and clinical scores.

I'm only up to the Method in the paper. This was slightly worrying, because HADS was used to measure depression and anxiety, and we know that HADS does not work well as a measure of depression and anxiety in people who are chronically ill with an activity-limiting condition.

So, I guess one question I have is 'how much of an effect did the controlling for 'depression' and 'anxiety' scores have?' I think the controlling could potentially dampen down differences between the cohorts and so not actually create a false difference. But, I'd like to know for sure if the identified differences are still there without the correction for depression and anxiety scores.

 

[Hutan]

Ah, here's a partial answer to my question, and it looks as if more data is in the Supporting Information

3.4 Group Comparison of NII- and DTI-Derived Metrics Without Controlling for Confounding Factors
Without controlling for confounding factors, Figure S23 (Appendix B.3 in Supporting Information) exhibits that the NII-RF in the ME/CFS patient group was significantly lower than those in the HCs in several association, commissural, and projection fibres. There were no other significant group differences in TBSS for NII-derived metrics between ME/CFS and HCs when no confounding factors were controlled for. In addition, there were no significant group differences in any DTI-derived metrics between ME/CFS and HCs that did not control for potential confounding factors.

So, it sounds as though the correction effort did increase the differences found, possibly making them a bit more unreliable. But the NII-RF being lower in ME/CFS in some fibres is perhaps a robust result.

RF is Restricted Fraction. I think that means areas where the cells are densely packed, possibly due to cellular infiltration, so water can't diffuse well at all (as opposed to areas of less densely packed cells, where diffusion is said to be 'hindered' and areas where there is free diffusion i.e. areas of water, oedema.). Hopefully @SNT Gatchaman or others can fix up my interpretation if needed.

The sample size of both disease and control cohorts seem big enough that the signals reported might be true. I guess it's just a question of how many possible things there were to find, and if this is a case of cherry picking.

Also note - they say that the RF was significantly lower. So, I assume that means less Restricted Fraction. I would have thought that means less possibility that inflammatory cells have infiltrated the area??

 

[Hutan]

3.5.1 Lower NII-RF Associated With Worse Mental Health and Increased Disability
Among all participants (including patients and HCs), significantly positive associations were observed between NII-RF and MCS or BDS across major white matter tracts (Figures 5 and 6, Table 3). Note that the regions where NII-RF significantly associated with MCS and BDS largely overlapped with the regions where ME/CFS participants exhibited significantly lower NII-RF compared to HCs.

That section of the paper reinforces that low NII-Restricted Fraction was associated with worse health. BDS is Bells Disability Scale - lower numbers mean lower function. So, a 'positive association' means higher NII-RF was associated with better function.

******
Diffusion Basis Restricted Fraction as a Putative Magnetic Resonance Imaging Marker of Neuroinflammation: Histological Evidence, Diagnostic Accuracy, and Translational Potential
That 2025 paper discusses the Restricted Fraction measure.

Here's the abstract:

Diffusion basis spectrum imaging–derived restricted fraction (DBSI-RF) isolates the low apparent diffusion coefficient water signal attributed to cellular crowding. It is therefore proposed as a putative magnetic resonance imaging (MRI) marker of neuroinflammation.

The purpose of this narrative review is to evaluate animal and human studies that compared DBSI-RF with histopathological benchmarks and clinical parameters. Across inflammatory demyelination, viral encephalitis, traumatic brain injury, and neurodegenerative disorders, DBSI-RF correlated moderately to strongly with immune cell density and distinguished inflammation from demyelinating or axonal pathology. In acute multiple sclerosis, com-bined isotropic fractions predicted lesion evolution, clinical subtypes, and deep-learning models that included DBSI-RF classified lesion subtypes with high accuracy. DBSI-RFmight also be used to track putative neuroinflammation associated with psychosocial stress, mood disorders, and anxiety disorders.

The strengths of the method include sensitivity to subclinical changes and the concurrent mapping of coexisting edema, demyelination, and axon loss. Limitations include non-specific etiology features, a demanding acquisition protocol, and limited large-scale human validation. Overall, DBSI-RF may demonstrate a promising diagnostic and prognostic accuracy, warranting standardized, multicenter, prospective trials and external validation.

Overall, DBSI-RF is hypothesized to serve as an MRI marker of neuroinflammation, since cellular infiltration and glial activation in neural tissue increase the density of cells. Thus, the fraction of the restricted diffusion compartment is also elevated [16–21].

In optic neuritis, the DBSI restricted fraction increases with the number of DAPI-counted nuclei and decreases with anti-inflammatory treatment.

It's clear from that abstract and quotes that RF is seen as correlating with immune cell density and a possible measure of neuroinflammation - more RF indicates more neuroinflammation. But, this Shan study found low RF in ME/CFS..... I don't know if the Shan et al study are reporting things differently?

The abstract of the 2025 paper also calls this measure 'promising' and warranting trials and validation in humans. Clearly, Shan and the team are using cutting edge technology, which is great, but it means it's a bit hard to know what it means.

 

[DMissa]

Good to see more Aussie research that (at least on first inspection until people who understand the details weigh in) appears to be rigorously conducted

 

[DMissa]

They are also suggesting a change in cellularity although I doubt they can pin that down to microglia, which would be the inflammatory cell. They cite NAkatomi but the signal in Nakatomi's study was not in white matter particularly. It was mostly down in midbrain and brainstem I think. And it was not replicated.

It might be that this is finally going to give us evidence of structural change in brain of a low-grade inflammatory type. However, (1) they point out the inconsistency of previous studies and this one may be no different and (2) it may be better to analyse this in terms of the raw data - water, cell and fibre changes, without premature labelling as inflammatory.

From the paper: "This study has some limitations that should be acknowledged. First, although the NII model offers biologically informed metrics, it is still an indirect measure of neuroinflammation and does not differentiate between specific inflammatory cell types or processes. Validation with other neuroinflammation-specific techniques would strengthen the interpretations"

It seems they are cognisant of this, which is great.

 

[Hutan]

Just coming back to this because it is so puzzling and I'm trying to find what I am not understanding. The Yu/Shan 2026 ME/CFS study is very clear that the Restricted Fraction is lower in people with ME/CFS.

Compared to HCs, ME/CFS patients exhibited widespread white matter abnormalities, including significantly lower NII-HR and NII-RF

The Yu/Shan study cites a 2020 study of people with obesity.

The NII model has been successfully applied to detect neuroinflammation in multiple sclerosis (Wang et al. 2011, 2015), Alzheimer's disease (Wang et al. 2019, 2024), and obesity (Samara et al. 2020).

That 2020 obesity study says in its abstract:

In both cohorts, the obese group had significantly greater DBSI-derived restricted fraction (DBSI-RF; an indicator of neuroinflammation-related cellularity)

That study claims that it is the high RF that suggests neuroinflammation in obesity.



Everything I can find suggests that it is a high Restricted Fraction that indicates increased cellularity, and that's an indicator of inflammation.
e.g. this:

Preliminary studies suggest that DBSI-derived metrics can putatively capture neuroinflammation in diseases like [Alzheimers AD] [33]. Ex vivo DBSI on human AD brain tissue, combined with immunohistochemical staining of microglia (Iba-1) and computational modeling, has shown increased RF in white matter compared to controls, aligning with microglial activation and cellular debris in AD [34]. These early findings, along with rodent models of AD [35], indicate a potential for DBSI-RF to quantify neuroinflammatory components in neurodegenerative disorders.

 

[Jonathan Edwards]

After all the discussion about glymphatics and brain water I do just wonder whether people with ME/CFS might have changes in all these measures as a result of lying flat more. It might be the opposite of normal pressure hydrocephalus where there is too much water outside the brain rather than inside. Lying flat has a siginifcant effect on hydrostatic pressures affecting water flux.

 

[ScoutB]

@Hutan I somehow ended up pondering this for a few hours this evening.
TLDR: It seems like they might be using the name "NII-RF" to mean kind of the opposite of what other papers are calling restricted fraction.

In the Kéri, S. 2025 paper you linked earlier, they say

In DBSI, water diffusion in cellular structures is modelled as a restricted isotropic diffusion fraction (DBSI-RF), typically defined by very low apparent diffusion coefficients (0.3–0.6 µm2/ms). This restricted fraction (RF) is interpreted as the volume fraction of water trapped by cells (e.g., inflammatory cells).

It sounds like roughly they are breaking the diffusion (of water while it's being pushed around by magnets) down into components going in different directions as well as an "isotropic" component that corresponds to the amount of diffusion going equally in all directions (expanding motion basically).

Then I think they interpret the spots where that coefficient of isotropic diffusion is "small" (0.3–0.6 µm2/ms) as areas where there are lots of cells locking up the water. (?)

Meanwhile, in the NII Processing section of this thread's paper, they define "NII-RF" as

NII-derived hindered fraction of restricted isotropic diffusion (D ≤ 0.3  μm2/ms)

I think their "D" is again supposed to be a coefficient telling you how much of this "isotropic" diffusion there is at a given spot. If I'm right about that, this would explain the discrepancy, as then the thread's paper is defining "NII-RF" to be <0.3 while Kéri, S. 2025 is using 0.3-0.6.

In the discussion, this thread's paper also says:

Lower [NII-RF] reflects more inflammatory cellularity, these positive associations imply that less cellular infiltration is associated with better mental health and better function.

Which I think confirms that their "NII-RF" measure is doing the opposite of what other people's RF measure is.

Very confusing! As if papers didn't already cite each other getting the results completely backwards often enough already...

 

[SNT Gatchaman]

We'll probably need to dig in to their referenced articles to try and understand the concepts behind these various NII- measures. First, here's a quick review of the basic MRI diffusion imaging (which this new technique is said to improve upon). Most of this is cribbed from Radiopaedia.

The basic idea is looking at how freely water molecules can randomly move with Brownian motion. (Remember the Hitchhiker's Guide to the Galaxy and the discovery of the Infinite Improbability Drive, with its freshly brewed cup of tea )

Water molecules in CSF have unrestricted movement (isotropic). An abscess would contain a lot of pus with dead neutrophils, so water can't move about so freely (anisotropic).

In normal brain, white matter tracts have nerve fibres running in parallel that encourage motion in the same direction. So with diffusion tensor imaging you look at the eigenvalues and eigenvectors of a 3x3 matrix (don't ask about the maths ). You can then do tractography to plot the location of normal white matter tracts or assess the health of the fibres in the tracts.

The terms used in DTI are —

Mean diffusivity

• The average magnitude of molecular displacement by diffusion
• The higher the MD the more isotropic the medium
• aka Apparent Diffusion Coefficient (ADC)
• We look for low ADC for something with very restricted diffusion, like pus or tightly packed tumour cells.

Fractional anisotropy

• Reflects the directionality of molecular displacement by diffusion and varies between 0 (isotropic diffusion, like CSF) and 1 (infinite anisotropic diffusion in a specific direction)
• Shows how directionally biased the diffusion is — high in healthy white matter where water has a clear preferred direction, but low in areas with poor structural organisation

Axial diffusivity

• "The longest eigenvector"
• In white matter tracts measures water movement parallel to the axon along its length
• Might be within the onion rings of the myelin sheath
• Intact axons encourages water to move freely alongside → higher axial diffusivity
• AD is reduced with axonal injury

Radial diffusivity

• "The average of the two shorter eigenvectors"
• Measures water movement perpendicular to the axon
• Restricted by intact myelin so should be relatively low
• Increases when myelin degrades (allowing water molecules to more easily move outward and away from the axon)
• Could decrease if further compacted myelin is laid down